Attack Analysis:
The goal of the Abele brothers has always been to determine what happened to the Grunion. Although some may disagree we feel that the evidence is strong enough that we have determined its location to at least make the next step in finding out what happened.

Below is the information we have about the attack. In light of our readership, particularly submariners, hopefully someone can help develop one or more viable hypothesis as to the demise of the Grunion.

It should be pointed out that there are some comments about the crew (shoddy construction, forgot to pull the firing pin) that should be taken with a grain of salt. There were major operational problems in the beginning of the war both with the torpedoes and with the subs themselves. To leave those comments out, in my opinion, would be a disservice to finding the truth.

There are three witnesses (diagrams and dialog) and a number of other bits of ancillary info.

Aiura: (Aiura was the military commander on the Kana Maru) Yutaka translating:

“The escort subchaser also came in and out the fog, at last we lost contact and the night came. KOANO MARU again went on alone in the foggy Bering sea toward KISKA. At July 30 08:00 we reached at the north of Kiska Is. about 20 nautical miles apart. But the dense fog prevented us to approach. We were forced to drifting and waiting the fog getting thin. The fog was getting thin for a moment and back to dense. We could do nothing but waiting. This day whole day the fog was dense and we were impatient. 15:30 A friendly seaplane fighter[Pete] ditched near us and we picked up. The plane and a pilot were both safe. The pilots were so young as just graduated his boy air school, similar age of my[S.AIURA] son. I was impressed with his figures that do his duty in the Northern sky. It was a happening that our ship saved him but I was so glad that we could help him. At the evening the fog still dense, we were alerting the enemy submarine attack. 17:15 We turned outside the open ocean, under 15 knots speed maneuvering zigzag course, decided to enter the KISKA harbor next morning.

July 31 Next early morning we again reached off KISKA harbor but the fog was still dense. We are drifting and waited. 04:40 The fog became a little thin and we can get our position by astronomical observation. We confirmed the altitude and latitude fixed the course toward the KISKA.

Enemy Torpedo Struck Home

05:15 We were avoiding the “MacArthur’s reef’ and at 158 degree 12 nautical miles distance of Segula Is. changed course toward 255 degree.

[*2] 05:47 “Torpedo! starboard fore!” Suddenly the signal master WAKISAKA first sergeant shouted. I saw two torpedo wake overlapped at I 00m starboard fore in the course crossing 45 degree with us, rapidly approaching. I at once ordered “Full turn starboard”. As KANO MARU went fast and the rudder turned much degree, the ship change the course rapidly toward right. I prayed the god and got tense for few second that was the most intolerable moment in my life. One torpedo wake passed after the stem we could avoid it, but other one hit the machinery room starboard side where was my back below and large explosion and sound occurred that was like a rumbling of the hell ground.

At the same time the main engine instead of its usual rhythmical sounds, but made two or three times of inertial dull movement and stopped. I was shocked by the force from the bottom and seized unconsciously the handrail and the base of compass. In a moment the machinery room was flooded whole, main engine lost power. We could not go anymore. Also generator, radio communication equipment and other auxiliary machines absolutely stopped. It was my disappointing but I had nothing to do.

The crews and soldiers seemed they did not feel fear at all and was vigorously preparing anti submarine combat or launch work of seaplane.

Lucky Dud Torpedo

This time we found a periscope of the submarine at very near right fore. Immediately 8em gun and 13mm machine gun started shooting. 8cm gun has less possibility to hit the submarine, but we thought the sounds of the gun was the only way to tell the KANO MARU’s crisis to the KISKA base. And also the 13mm machine gun fire were useless against the sub under the water but the splash aids the aim of 8cm gun crews. Further more the 8cm gun on the aft poop deck was malfunction by the heavy shock of torpedo explosion.

The periscope that had been right fore, gradually moved to right aft. 05:57 From the right 157 degree 300m distance the sub shot second salvo. One torpedo wake line from right aft passed below the ship bottom at about the bridge. It was no harm. How lucky we were I To transmit our crisis to the KISKA base, we planned as the last way to use the seaplane that we had picked up yesterday. The plane was still hooked under the derrick. The whole crews set the plane on the sea surface by only man power. The pilot, NMRASAWA the second class air soldier, tried much efforts but the engine never started so we had no way but accept the fate. The periscope sometimes appeared and moved from the stem to the portside. 06:07 From the left 135 degree very near the sub shot third salvo. Three torpedoes wake came toward us. Perhaps the sub shoot whole the rest torpedoes in the tubes and intended to finish us. I gave up whole, thinking the torpedoes must finish KANO NLARU and hard to breathe in more than ten seconds. Two torpedoes hit! but nothing happened! One torpedo struck the bridge fore, No.2 cargo hold. But unexpectedly it didn’t explode, lost its head and the rest body floated on the water tail down and about 0.5m part dry. Next one torpedo struck amidships portside, but also dud. Last one torpedo went away passing near ship stem. How lucky we are! I thank to the God protection.

06:10 Then we find the periscope at left 13 5 degree about 400m distance. Our forecastle 8cm gun and 13mm machine gun again started the fire. The sub kept the periscope up and moved calmly ignoring damaged KANO MARU. We clenched our fists but had no way to do. [*3] Then the sub seemed to begin to surface. The conning tower made ripple on the surface and the wave began washing the conning tower. I think the sub was unable to sink KANO MARU by the torpedo ( reload the stocked torpedo to the tube needs much minutes ) so finish KANO MARU by its gun or the sub thought KANO MARU could do no harm any more. Just then a 8cm gun shot hit the washing wave, made water column and dull water explosion sound. Also we saw the swell of heavy oil. All crews shout ‘BANZAI!’

Aiura: second source:

This day’s antisubmarine combat action aimed only the periscope so continued intermittently about 20 minutes. At last we found the periscope at left 135 degree about 400m distance, immediately start firing. The fourth shot that was the 84th counting from the first shot got directly the target.

About this submarine sink, later coming mine layer ISHIZAKI and other ships observed much oil spouting, piece of lifeguard buoy, chips that seemed to be the material of submarine decks, and other many things. They confirmed the sinking and radioed to the Fifth fleet and combined fleet chief of general staff through the fifth guard command. [*4]

More important info is about the torpedo. They, IJN Kiska base soldiers, took the rest of the torpedo which lost the head and floating near Kano Maru. They towed the torpedo body by boat to the Base, and observed. Aiura reported, apparently the head and body connection was irregular work. Because it seemed more than 30 bolts hole exists around the head-body connection part, but only three bolts were used and the rest was partial 10cm length silver-wax work not by welding.

Aiura said it is apparently not regular navy-yard work.

Aiura also reported, he thought the maneuver of the sub was strange. The sub seemed to have approach to the aft behind of Kano Maru shadowed from the forecastle deck gun, but is was too near to keep safe from the gun fire. Forepeak deck gun could at least bow or aft-end of the submarine. And Aiura said also it was strange 5 in 6 torpedoes were dud. 2 of them hit but not exploded. Aiura said the torpedo men must forgot the normal procedure to unlock safety pin.

AIURA’s Torpedo Analysis

Second Witness: RIKIMARU NAKAGAWA, ARMY Medical Sublieutenant

While I was looking aft on boat deck(port) in front of my cabin, I saw bubble running on the surface figuring half circle just 2 or 3 hundreds meters apart from shipside. I shouted ‘Must be Submarine!’ Then just at the head-end of bubble running, big black-brown water arose, something oily afloat on the surface, after a while a black thin bar appeared on the surface then fell down and submerged. I in spite of myself cried out ‘Good, You got what you deserved!’, and I am convinced the submarine was sunk by the shell. ”

Rikimaru Nakagawa.jpg

Third Witness: was a “contract newspaper man” who visited the site after the attack.


I had got on a motor launch and left KANO MARU from portboard.

The boat ran over the stem and went to the starboard side of the ship.

Then I saw at left side of the boat, about 200m apart from my boat, that was 500m from KANO MARU’s stem, something was afloating on the surface. That were two cylinder, like oil drum, upright about 0.5m over the surface.

I found that objects but couldn’t approach so I didn’t understand what they were.

When my boat went on to the starboard and aft side of the KANO MARU, I saw the same two objects at the front of my boat, 50m distance, that was about 400-500m from the KANO MARU’s stern.

Again I didn’t understand what they were.

Later I saw a torpedo at land, that was without explosive warhead, picked up by the same(my) DAIHATSU boat.

Then I heard from Navy men (about the torpedo), and I understand what I had seen were torpedoes that lost its warhead and afloating upright.

SYOWA 17(1942) August 3rd PM 03:30
Army contract newspaperman

Kenji provided a sketch. Two copies are provided each with slightly different annotation


Kenji Hamada -1.jpg

Few submariners think that a 3 in shell that hits the wake caused by the conning tower would sink a Gato class sub. However we must consider the proximity of the 84th shot and “dull water explosion” Whatever happened was in some way amplified by the shot. Most submariners are aware of the poor quality of the MK 14 torpedoes. They pre-exploded, would run low, did not detonate upon contact and occasionally would circle around. In addition the submarine batteries were subject to explosions and fires. The exterior torpedo doors were closed manually and such things as a displaced gasket would be devastating.

It also should be noted that the sub did not implode / explode which would have happened if the compartments had been closed off. This tends to imply that what ever happened was rather sudden.

On the slide path there appears to be some debris, some fairly large, and about 25 ft of the bow of the sub appears to be buried or blown off.

133 Comments for 'The Attack Analysis'

    October 19, 2006 | 1:23 am

    Was there some comments saying that one of the torpedoes may have looped around and hit the sub? Is it also possible that there may have been an accident in the bow torpedo compartment? (Ala the Kursk)
    Could it be that somehow a torpedo exploded either in the tube or out of it and heavily damaged the bow and/or other compartments and opening it to the sea? Being bow heavy, and with possibly one or more compartments damaged or flooded, the captain would have tried to surface imho. With the sub negative bouyancy, a hit or two from the ship shelling the sub could have caused flooding that may have been too much to counteract and would have sent it to the bottom with no hope to surface. The weakened bow may have snapped off on impact or may be still there buried in the sediment not visible to the sonar.
    It may not be likely or even probable, but may explain why it sank so fast. Hopefully once they get some footage from the site we can find out.

    October 21, 2006 | 6:03 am

    If the debris indeed included torpedo bodies, then it would imply a catastrophic explosion in either the forward or aft torpedo rooms. Since the torpedoes would have been crushed at a depth of more than several hundred feet, the torpedo room must have vented to the sea above the rated depth of the hull. The bubble path suggests that the boat turned on its axis as it sank, and the rush of fuel to the surface inside the path indicates bunker rupture as the boat exceeded crush depth. Perhaps one of the reloads had a “hot run” which would have served to arm the warshot, with a consequent shock detonating the warshot on the rack.

    October 25, 2006 | 1:55 am

    True, just doing a little mental thinking on possibilities on what may have happened. Won’t really know much till they get a look at the wreck itself. The fact that the wreck looks reasonably intact seems to suggest that it was open to the sea near the surface or it would most likely have imploded as it reached crush depth and would be in numerous pieces on the bottom.
    Reasoning that something catastrophic happened onboard is plausible as it’s hard to believe just a shell hit or two from the ship would have been enough to sink the Grunion that fast. Always the chance for a million in one lucky hit, but still hard to believe all the same.

    Howard A. Sanders
    June 7, 2007 | 5:26 pm

    I’m not sure how this fits into the information given here but I came across copies of several pages out of a book that I not no the title. The top of the page just says Trigger. Anyway, the information was written by someone who received a transmission from the Grunion and it says, ” FROM GRUNION X ATTACKED TWO DESTROYERS OFF KISKA HARBOR X NIGHT PERISCOPE SUBMERGED X RESULTS INDEFINATE BELIEVE ONE SANK ONE DAMAGED X MINOR DAMAGE FROM COUNTERATTACK TWO HOURS LATER X ALL TORPEDOES EXPENDED AFT… He went on to say that this the last transmission by the Grunion. The interesting part is what he says in the next paragraph. ” Years later I read an account of an interview with a Japanese sub skipper, now master of an American-owned merchant ship operating out of Yokohama. As skipper of the I-25 he had made three patrols from Japan to California. On one return trip, when passing the Aleutions, he had torpedoed a surfaced submarine. The date he gave was July 30, 1942, which tallied exactly with our interception of Grunion’s last transmission.”
    Does this account agree or contradict the information gathered so far?

    Paul Popejoy
    June 22, 2007 | 3:02 pm


    Clay Blair reports (in SILENT VICTORY) the following:

    “Patrolling of Kiska on July 15, Abele attacked a destroyer, firing three torpedoes which missed. Later that same day he attacked three ships he believed to be destroyers. [Rear Admiral] English credited Abele with sinking three destroyers, but postwar analysis showed they were patrol craft of about 300 tons each, only two of which sank. On July 28, GRUNION attacked an unidentified ship, fired two torpedoes, and missed. On July 30 off Kiska, Abele reported heavy antisubmarine activity and said he had ten torpedoes remaining. Colclough ordered him back to Dutch Harbor.

    “Nothing more was heard from GRUNION. She disappeared without a trace, like SHARK.*

    “* Some believed she had been sunk by a Japanese submarine, I-25, which reported sinking a submarine in the area. Subsequently it was learned that I-25 sank a Russian submarine, one of four en route from Vladivostok to Mare Island for a lend-lease overhaul.”

    Paul Popejoy
    June 22, 2007 | 3:30 pm


    The translation says “the wave began washing the conning tower” and then says “Just then a 8cm gun shot hit the washing wave, made water column and dull water explosion sound. Also we saw the swell of heavy oil.”

    If the “washing wave” was the wave “washing the conning tower” then the shot that “hit the washing wave” may have hit and exploded in the conning tower or some nearby part of the submarine, causing enough damage for the Japanese to see “the swell of heavy oil,” but I suspect the submarine was only damaged and not destroyed.

    The key appears to be eyewitness Rikimaru Nakagawa, who observed the “bubble running on the surface figuring half circle just 2 or 3 hundreds meters apart from shipside” followed by “at the head-end of bubble running, big black-brown water arose, something oily afloat on the surface, after a while a black thin bar appeared on the surface then fell down and submerged.”

    FWIW, Mr. Nakagawa’s testimony appears to describe a circular-running torpedo returning to hit Grunion: the steam-powered Mk XIV torpedoes then in use certainly left a trail of bubbles, circular runs were known to occur with this type early in the war, and the”big black-brown water arose” is consistent with an underwater torpedo detonation.

    Examination of the wreck may be more conclusive, but based on this witness I would say we can hazard a fair guess that Grunion became frustrated with torpedo failures and attempted a surface engagement, was hit causing minor damage, and then resubmerged and went back to torpedoes, one of which circled back and sank Grunion.

    Jim Lucas
    July 30, 2007 | 2:20 pm

    I spent a few days last week with Russ Dieselberg [My Uncle and Uncle of L.H. Doell Jr R2C ] .in atlanta last week. also had lunch with Rhonda Raye in Cartersville Ga. This Info is really interesting. There are so many things coming to surface over this discovery, that are changing many lives.
    Thanks for the E mail from my step cousin Nancy Springer. Hope to hear from you soon. I am doing some local research on the biography of Junior Doell.

    Greg "Gunner" Stitz
    August 25, 2007 | 3:07 am

    I think I can shed some light on why the After Battery Room hatch is open.

    GRUNION had a single gun mounted aft of the conning tower.

    If, after having the dud torpedoes, GRUNION decided to surface and finish off KANO MARU with her gun, then the gun crew would have formed up in the crew’s mess, directly under this hatch, and would have even likely loosened the dogs in preparation for throwing it open to man the gun.

    David Dodge
    August 25, 2007 | 11:10 pm

    OK, if the After Battery Room “scuttle” was loosened in preparations for surface attack. Could the 3″ shell have hit a high pressure tank in the pump room ( located, I believe just ahead of the contol room – conning towers washing wave) blowing the scuttle open and thus allowing a very fast flooding of the center of the ship?

    Ed Walson
    August 26, 2007 | 3:33 pm

    When the boat is submerged for any time period the internal pressure can build up (from a variety of causes, chiefly venting compressed air) to a point where the overall pressure inside the pressure hull is slightly in excess of atmospheric pressure. In a normal surfaceing evolution the upper conning tower hatch is opened first (normally it is the ONLY hatch opened). This is done by ‘cracking’ or slacking the hatch dogs off a small amount before actually surfaceing the boat. When the conning tower hatch breaks surface the higher internal pressure acting on the hatch causes it to spring open against the slackened ‘dogs’, which keep the hatch from slamming open during the time it takes to equalize with sea pressure. When this happenes there is a voice report made “Hatch is Cracked” it can take several seconds to equalize this pressure, at that time the hatch wheel is fully opened. There is also a single manually operated spring loaded ‘catch’ which must be pushed aside to allow free movement of the spring assisted hatch to the open position. There can be quite a lot of energy built up at this point and an over eager quartermaster could be lifted off his feet if he acted too soon.

    It is possible that if a gun crew were standing by in the mess room for a surface gun action that the upper hatch dogs may have been prepared for surfaceing in this fashion. I don’t think they would ever have been fully backed off or retracted to the full open position.

    An other matter here is that Gato class boats (at least later) were equiped with a second hatch assembley that bolted on the flanged hatch combing inside the compartment. These secondary hatch assembleys were fitted for war patrols as protection against depth charges or other explosions (or collisions) which could effect the actual deck hatch or hatch seals. This secondary hatch plate was equiped with an oblong personnel access hatch also held in place with a ‘strong back’ type of hatch dog. Travel up and down through this 2nd access hatch was not easy or quick. I don’t know if the ROV got a look down that hatch or not, it would be interesting to see what condition this secondary hatch was in.

    The portable hand rail shown to be in position outboard of the deck hatch was normally ‘stored for sea’ as a routine. It is possible that it was left in position to assist the speedy deployment of a surface gun crew through this hatch.

    August 29, 2007 | 1:50 am

    Grunion’s sister ship, the USS Growler, sustained heavy bow damage when it rammed a small Japanese freighter in February of 2003. It would take some force to blow it off although a premature torpedo explosion, either in the forward room or just after firing or even from a circular run may be sufficient, if not a direct hit, to render such damage. The late Richard H. O’Kane, himself a survivor of a circular run in October of 1944 on the USS Tang, wrote of such a theoretical possibility, the damage from which might have resulted in the ultimate demise of the USS Wahoo. Coincidentally, the Wahoo was recently found in La Perouse Strait, where it was sunk.

    August 29, 2007 | 6:23 am

    Error correction…the USS Growler rammed the Japanese freighter on February 7, 1943 and not in 2003.

    August 29, 2007 | 8:22 pm

    Error correction…the USS Growler rammed the Japanese freighter on February 7, 1943, and not in 2003.

    Pat Householder
    August 30, 2007 | 3:08 am

    As a former diesel submariner, it seems entirely plausible to me that a shell hit in the conning tower would cause the lower CT hatch to malform, allowing the flooding CT to also flood the control room below.

    While a fleet boat could certainly deal with a flooded CT, it could never survive a flooded CT and Control Room and would settle towards the bottom, eventually imploding any sealed off compartments.

    The few photos seen seem to support that hypothesis, with the relatively intact conning tower structure and sail. I’m anxious to see more photos of the remaining hull structure of the submarine, but based on the AB hatch being open, it appears that section may not be crushed either and possibly flooded before reaching crush depth.

    It is also possible, based on the missing bow, that she suffered a circular torpedo hit, or had a detonation in a tube. It’s interesting that the massive damage only extends to the fwd edge of the FTR escape compartment, meaning that the back half of the torpedo room was not shredded.

    A. Kidd
    August 31, 2007 | 1:37 am

    I believe that if Gruion came up bow first;deliberately using this maneuver to speed a surface action. The bow was mistaken for the conning tower. The 13mm shell could have thus penetrated the forward torpedo room and exploded detonating one or more of the torpedos there. Thus, promptly sinking the USS Grunion and explaining the missing bow, open hatches and unusual manuvering, bubble path as the after gun was to face the target., Bubbles came from partiallt opened hatch.

    Ed Walson
    September 1, 2007 | 7:02 pm

    Grunion had earlier reported that it had ten torpedos remaining on board. For the sake of arugument I am assuming this was six tube loaded in forward torpedo room and four tube loaded in after torpedo room.

    I believe the third ‘salvo’ (firing position at 0607 hour) were fired from the after torpedo room. Note that Kana Maru was dead in the water and not moving forward. The attack ‘angle on the bow’ was Port 135 degrees (a better ‘aspect’ angle than the other two attacks).
    The ‘gyro angle’ manually set into the three MK 14-3 torpedos would have been very close to each other as very little ‘spread’ was required to lead the nearly stationary target.

    These weapons were fired from very ‘close aboard’ something in the order of 300 to 400 meters-yards. The MK 6 exploder in the MK 14-3 Torpedo had a fixed ‘enableing distance’ that the torpedo had to travel through the water before all of the internal exploder components were in a physical position to allow the train of initiation charges to cause a contact dentonation. I have been unable to find out exactly what that distance was (Com Sub Pac could tell us that is they get interested in this) but this could account for the two ‘dud’s altho there were other known problems with this exploder. This element may have had an effect on the second firing position (0557 hour) in which a single torpedo appeared to ‘run deep’ and elcewise failed.

    The third salvo has witnessed two ‘dud’ hits about where they were supposed to hit. The third weapon opens to the right and passes behind the target. This could easily be the start of a ‘circular run’. The rudder control (steering) of MK 14-3 is a phenmatic servo which has three positions, right full rudder / left full rudder / or neutral (center). The rudder control is not graduated in small increments. It corrects torpedo path by very fast movements to full left or right or middle settings. It receives its instructions from a mechanical device that senses the gyro position during the run to target.

    USS Tang SS 306 was a victim of a circular run with eye witness survived. The reports estimated approx 20 seconds after firing the torpedo came full left circle and hit after torpedo room and flooded after three compartments.

    If Grunion fired the last three weapons from the after torpedo room her heading at time of firing would have been approx 135 degree compass. I think that immediatly after firing the Grunion made a hard left turn, increased speed (to assist with trim control) and tried to come to heading of something 080 degree which would have opened the target, hidden or shadowed from the over active 8CM gun on target bow, and allowed another firing solution for the remaining (largely useless) torpedos.
    Having just (1) fired three torpedos of approx 3,000 lbs each from the stern, (2) increased speed and (3) made a hard rudder movement her ‘fine trim’ and ability to maintain 63′-67 ‘foot periscope depth was temporarly compromised. The stern planesman was (reasonably) unable to control the angle of the boat and as a result the sail ‘broached’. (Exposing her Port Side) Certainly not the first time this particular trim-control problem has happened. Grunion had a rough heading of 045 degree compass at this point. It appears to have nearly completed her turn to left (port).

    And then the circular running last torpedo impacted the forward torpedo room. This accounts for the “head end of bubble running” and “big black-brown water arose” and “dull water explosion” and “bubble running on surface figuring half circle” (eye witness account Rikimaru Nakagawa, from Kana Maru main deck level).

    I cannot envision how a 8 CM (roughly 3 inch) cannon shell could do all of this damage. I think that a good look at the video from the ROV will show the damage from the shell. It will be interesting what the Navy will have to say. The scandalous ‘MK 14 Torpedo PROBLEM’ is not yet lost in Navy Submarine memory. (or the USS Scopion for that matter) If I were a Weapons Officer in Com Sub Pac today I would already have run a few computor simulations just to see..? Even if it wasn’t a circular run, the Grunion sank because the Torpedos didn’t function correctly. The second firing position should have finished the short fight. There are officially only two USN boats (USS Tang SS 306 and USS Tullibee SS 284) known to be sank by circular runs. Confirmed because credable eye witnesses survived. There are other cases where doubt remains…Grunion is most certainly one of them.

    I served as a Torpedoman on Gato class boats in late 1960’s and remember firing ‘excersise’ shots with MK 14-5. We always rigged the ship very carefully during these firings, the Mk14 (in high speed setting) travels at 47 knots and at +3,000 lbs. nobody wanted to get hit by one even if it didn’t have a war head.

    September 4, 2007 | 11:21 pm


    I´m new to this blog, but as a submariner I think I agree with Pat Householder. The CT hat is completely deformed outwards, this can only be the consequence of an explosive force within the CT. Wether this came form the 8cm hit or an internal explosion somewhere else I can´t ascertain. Remember Kursk: the torpedo compartment was literally missing but the rest of the hull looked intact… but in the inside several pressure tight bulkheads had been destroyed.

    If such an exposion (in the torpedo room) had taken place, it could have spread aft, blowing open the CR to CT hatch and then deformed the CT-bridge hatch, at the same time blowing open the “cracked hatch” aft.

    So far, it´s only speculation, at least until an image can be obtained of the conning tower at the supposed shell hit point .

    Kevin Kelleher
    September 5, 2007 | 3:34 am

    Fascinating story. Iread “Blind Man’s Bluff” this stuff is even more interesting! God rest their souls.
    Kevin Kelleher, Big Sky MT.

    September 14, 2007 | 2:12 am

    The suggestion that the ‘Torpedo Room’ neglected/forgot to ‘pull the firing pin’ is not credible ; when those fish were loaded they were iready for the job they were designed to do – that is, once they have come up to firing depth and the impeller on the exploder has completed the required number of revolutions to arm it. {Of course, this was early in the war, July,1942, when many of our boats were having problems with faulty torpedoes.) It is interesting to read the comments that have been proffered as an explanation of Grunion’s last moments. As more information is forth-comming based on pictures we have not yet seen, perhaps that annalysis will give us more definitive answers to our questions. Bob Sands, TM2/C, USS Paddle (SS263)

    September 20, 2007 | 1:06 pm

    “The portable hand rail shown to be in position outboard of the deck hatch was normally ’stored for sea’ as a routine. It is possible that it was left in position to assist the speedy deployment of a surface gun crew through this hatch.”

    Photos of the USS LAGARTO wreck also show this hand rail lying on the deck (deck planking rotted away) atop the hatch.

    Salah Baker
    September 20, 2007 | 10:57 pm

    Ed Walson, what a great post!

    Thanks for the Footage Bruce, all is well with it.
    Ill send you a copy this weekend of what we did with it.

    Ed Walson
    September 23, 2007 | 9:00 pm

    I noticed that the Mine Layer ‘Ishizaki’ reported ‘observed much oil spouting, piece of lifeguard buoy, chips that seemed…to come from sumarine decks’. This ‘lifeguard buoy’ must be one of the two ‘Salvage Buoy’ systems carried on Grunion. These two buoys (approx. 4-5 foot diameter) were carried recessed and faired into the superstructure of the main deck just forward and to the port side of the two torpedo room main deck hatches.

    The buoys had a length of wire cable connecting them to a wish bone or ‘bail’ attachment to the torpedo room hatches. If the boat were disabled in shallow enough water (200-250 feet) that rescue were possible, this buoy could be released by use of a hand hydraulic pump located in each torpedo room. The buoy would float to the surface, the wire would pay out from a friction drum and ultimately the buoy was conected to the upper torpedo room hatch. This wire could be used by the ASR (Auxillary Submarine Rescue) Divers in various ways to assist rescue or salvage efforts of the boat.

    The point is that these Buoys carried information on an ingraved plate which indentified the submarine by name and hull number and gave other instructions to whoever discovered the buoy. This probably is where the Japanese acquired the name and hull number of the Grunion to start with! When Gato class boats made patrols in the 1960’s these buoys were typically welded down so that adverse sea conditons or other accidental means would not allow them to deploy at an inconvenient time.

    Also note the presence of this buoy in the oil and other wreckage at that location indicates that the the deck and superstructure forward of the forward torpedo room were destroyed at that time. Not from contact with the ‘underwater volcano’ on descent, or while sliding down the submerged slope.

    I believe this makes an additional case for the ‘circular run’ torpedo theory.

    Susan Abele
    September 25, 2007 | 12:33 am

    This comment is for Ed Walson. Ed would you please contact Bruce directly at Thanks.

    Susan Abele
    September 25, 2007 | 12:34 am

    Sorry, Bruce’s email is

    Doug Sego
    September 27, 2007 | 6:21 pm

    I’m a little confused by Aiura’s Torpedo Analysis Diagram, specifically the dashed line indicating a bubble path since the firing of the first salvo. Could this be a misinterpetation, or was there really a bubble path since the first salvo? I thought Aiura’s statements suggested sub tracking by Periscope sightings only. If there was a bubble path coincident with the sub’s location after the first salvo, that could indicate flooding or a stuck tube hot run.

    David Decrevel
    September 27, 2007 | 6:34 pm

    I very much tend to agree with Ed Walson’s senario as a likely cause for the sinking from the evidence we’ve seen so far. There were several other reports of ‘circular runs’ during the war besides those of Tang and Tullibee. Both Tang and Tullibee were on the surface when they experienced their problems, but other skippers reported circular runs while submerged. As the Mk. 14’s were later determined to run at least 10 feet deeper than set, a submerged boat faces the same danger, depending on how deep the fish were set. At that time of the war the policy was to set the torpedos to run beneath the target, so it is easily possible for a deeper than set torpedo to strike the firing boat when it is submerged at 60′ to 65′ periscope depth. The ‘bubble path’ can easily fit a torpedo wake and one of the few things I can think of that might create a similar wake would be if one of the shots from the Kano Maru had holed the main induction, however this would not result in the eye witness account of “head end of bubble running” and “big black-brown water arose” and “dull water explosion”. It would also make sense that the fish were fired from the after room, as the arc of the circle would most likely intersect the bow. Both Tang and Tullibee were sunk by torpedos fired from the forward room, and struck in the stern.

    At this point it appears to me that Grunion fired torpedos, one of which made a circular run and struck the bow in the Forward Torpedo Room just forward of the escape trunk. Additional support for this theory would be the evidence of, or lack thereof, implosion damage to the FTR. The pictures posted so far indicate to my eye, extensive implosion damage to other parts of the boat. The ATR seems to show this just forward of the aft capstan; the Conning Tower definately shows it; and the open After Battery hatch indicates it. As with the Scorpion, it become a matter of “if” and “then”. IF a torpedo struck the FTR and no water tight doors forward of the After Battery were closed, THEN then hatch could have been blown open by the pressure wave of the explosion. IF one or more of the water tight doors were closed, THEN the collapse of the bulkhead between the Forward Battery and Control, or more likely, the one between Control and AB, would cause a resulting pressure wave and could blow open the hatch. Whether or not Grunion was fitted with hatch ‘doublers’ at this time of the war, I do not know.

    Ed makes a very valid point. When and if it is finally determined what ‘event’ sank Grunion, the ’cause’ was the defective Mk. 14 torpedo.

    David Decrevel
    SS-328 SS-396
    Past Nat’l Historian USSVI

    Ed Walson
    September 28, 2007 | 7:03 pm

    To Doug Sego. I looked at the sketch provided by Aiura and concluded that whoever interpreted the sketchs and other after action reports added the ‘red’ numbers 1 thru 6 which I.D. the individual torpedo firings AND the ‘path of bubbles’ with the arrow. Aiura narritve was very experianced, factual and ‘seaman-like’ with vessel positions, correct angles on bow (from the elevated view point of Maru bridge) and specific times but did not mention the bubble track. Aiura did not make any guesses only facts which were probably copied into his vessel log book. I disregarded the red ‘path of bubble’ note, it came from a different witness (the non-seaman medical officer (at main deck level) and was added in by one translater or another.

    September 30, 2007 | 11:28 am

    Open hatch pics.

    Isn’t that the hatch rubber seal/gasket shown in the pics? It’s been looped completely around both the hatch and the outer hatch deck cover. Only a limited number of ways that could have happened.

    David Decrevel
    September 30, 2007 | 9:21 pm

    To Bob. I also believe it is the hatch gasket. It appears to be the correct shape and dimension, with hard, straight edges, and is a continuous circle. The hatch gaskets that I recall, were flat on the 3 sides that fit into the channel of the hatch, and the outer, or seating side, was in the shape of a triangle. As the decking is attached to the hatch, the gasket would merely have to ‘roll’ out of its’ channel and loop over the decking. This further supports the idea that the hatch was closed, and was subsequently blown open. If it was open, I can’t forsee any force that would cause the gasket to come out of the channel.

    Mike McMahon
    October 2, 2007 | 3:39 am

    For Ed Walson
    The last message from Grunion dated on the day they were lost stated that they had 10 torpedoes left, none in the after room. Bruce, can you post the last message on this site? In the encounter with Kano Maru, two different spreads of 3 torpedoes each were fired. After these 2 salvoes there was probably a reload activity in the Forward Torpedo Room, to load the remaining 4 torpedoes.

    Dr. Eduard Mark
    October 5, 2007 | 5:05 pm

    I have followed the search for the Grunion with great interest since its inception. I have no special knolwedge of submarines, but I am a professional historian with much experience of working with primary documents in foreign languages. Knowing well how even subtle mistranslations can lead to major errors of interpretation, I suggest that the Japanese documents so critical to understanding the Grunion’s fate be re-translated by a professional translater and checked by a second. The English renderings we have are so obviously awkward that there is room for doubting whether they convey the meaning of the Japanese originals as clearly as they might.

    Ed Walson
    October 5, 2007 | 6:27 pm

    All, ‘The Captain Beech’ (himself) when communications officer on Trirgger intercepted a garbled message from Grunion (and personally knew the wardroom officers of Grunion) states that torpedos aft were expended. So all of this torpedo action takes place from Tubes Forward. Starting the day with six tubes loaded and four on storage skids.

    At 0607 she fires spread of three from some distance (?) appox 135 degrees (target angle on port bow). Kana Maru is dead in the water, stationary target. Gyro angle of these weapons would have been very close togeather to effect a spread (say 5-10 degress max. separate). Grunion was firing at ‘Center of Mass’. Two of weapons hit where they are aimed (no. 2 hold & midships) duds. Third torpedo (sixth of the day) passes astern of Kana Maru. I have run some very rusty geometry on this. Assumed Kana Maru to be in the order of 600 feet long and a distance to target of 400 yards. This shows the sixth torpedo to open something in the order of 15-25 degrees in the 400 yard run distance. This MK 14 was acting erraically from the git-go. Projecting this out shows a very large diameter circlular run of approx. (using my assumptions) of 3.6 minutes.

    None of my figures are accurate but proportionally they fit togeather. There was a 630 lb. war head going somewhere…in the same time period the Grunion had her bow removed by an explosion of this magnatude. What is the likelyhood that it was another separate event?

    Gunion as submerged has near zero buoyancy (proably diving officer has her trimmed to be slightly negative to prevent accidental ‘broach’). Point of Gravity (or fore and aft balance) is in Control Room. Over all trim is slightly rough (witness the single broach) due to maneuvers (hard turn) and tropedo firing activity forward.

    Torpedo dentonates near/at forward torpedo room, breeches hull integrity of fwd room and I believe the forward battery compartment. All the heavy gear forward of forward room hatch falls away. (Forward bulkhead of Main Ballast Tank #1 is visable in photos of bow). This is six torpedo tubes, bow planes and associated hydraulic rams and motor, anchor and chain, forward capstan, structure of WRT and Bow Buoyancy all separate from the ship.

    Point of Gravity moves aft to some where around the after engine room or maneuvering room. The breeched forward battery compartment causes immediate electical failure leading to propulsion failure. The ‘hole in the water’ or bubble effect of the explosives caused all vessel forward motion thru water to cease. The boat settles by the stern and pivots to its new balance or trim points. Witness (non-seamen Medical Officer) mentions ‘black bar fell over’. This probably was the fully extented periscope as the boat slowly rotated and settled astern. This pivot also allows some fuel oil to excape throught the open ballast tank bottoms. But depending on the actual angle of the boat not all of the oil was lost, the oil remaining may have had an effect on the descent speed.

    I believe that the After Battery hatch was ‘sucked’ open by the expanding lower pressure ‘bubble’ created after the initial ”high pressure” hydraulic wave passed over. The After Battery compartment shows the same signs of collapse as the remaining compartments in the stern. I conclue that the ‘doubler hatches’ were indeed installed, and this event on the ABH did not allow flooding of the compartment.

    Gunion settled to the seabed stern first. Landed (bent rudder first) on a sloped seabed and slid down hill to her resting place. Drag marks or slide trail caused by the propellers and stern planes. It appears that the bow section did not scoop up much bottom material because the stern remained much heavier through out.

    David Decrevel
    October 6, 2007 | 4:43 pm

    Regarding the third salvo as reported by witness:

    “One torpedo struck the bridge fore, No.2 cargo hold. But unexpectedly it didn’t explode, lost its head and the rest body floated on the water tail down and about 0.5m part dry. Next one torpedo struck amidships portside, but also dud. Last one torpedo went away passing near ship stem.”

    The ‘stem’ is the bow or a ship. Reviewing the available picture of Kano Maru, it is difficult to determine if the bridge is forward, or aft of ‘amidships’, but if the translation is accurate, I would surmise that Grunion’s torpedo spread was stern to bow, and not vice versa.

    October 6, 2007 | 8:46 pm


    “Doubler Hatches” were a later war development as someone posted previously. For example; USS BATFISH didn’t receive them until her refit over the period of 01 Dec 44-30 Dec 44.

    Refit item; “Installation of safety plates for deck hatches”

    I’d disagree with your scenario only in minor details however;

    I have serious doubts that an external low pressure bubble would shatter the After Battery hatch locking mechanism as it is. My view; it’d take a sharp, violent force to do so…from the inside. Bottomline; two of the locking rods are snapped, and the third is deformed. You can also see the stainless steel liner that was around the inner lip of the hatch was stripped away and wrapped around the ladder (outward).

    If you enhance various photos of GRUNION wreck, you can see the curvature of the AB compartment “top” in pretty much the correct plane from the rear of the conning tower to the deck gun. I’m not totally convinced that it imploded. I suspect it’s a possibility that the Control Room and AB compartment forward bulkheads failed sequentially. Possibly one or both were damaged/weakened by the forward explosion. Which would also explain the catastrophic failure of the AB hatch locking mechanism (unless I got ripped off when I bought my diploma from the “Jethro Bodine Internet School of Fluid Mechanics”).

    Cons against this argument; (1) It sure looks imploded. (2) If you lay the photos out in a mosaic against a diagram of a Gato class sub, the “high” points in the wreckage all correspond with internal compartment bulkheads. (3) Compartments aft of the AB compartment are all definitely imploded.

    Pros; (1) As stated. (2) Still working on that. (3) Compartments aft of the AB compartment are all definitely imploded. Shockwave generated by collapsing forward compartment bulkheads vented through AB hatch, which was not designed to defeat a massive internal over-pressure/hydrostatic event. Bulkheads/hatches were, and held long enough for the compartment to implode.

    If GRUNION impacted stern first, how’d the cavity in the bow get “dished in”? I’m totally baffled. And if it hit bow first, why didn’t the MBT #1 and the torp drain tank get smashed in?

    David Decrevel
    October 7, 2007 | 1:03 am

    Ed….was wondering if you would crank up your rusty geometry one more time, and see what difference (if any) might show up IF the spread was from aft to forward. If the 6th fish passed the bow instead of the stern would it make any difference? Also, remembering back to your TM days, what was the arming distance of the MK 14? My memory cells seem to recall 450 yards, but then I did spend way too much time in the battery wells.

    Bob, I never completed the curriculum for “Jethro Bodine Internet School of Torpedo Explosive Forces”, but do agree that IF such an event did occur in the bow, the chances are quite good that at least the watertight door/bulkhead flappers between the forward room and Forward Battery would be damaged; not too sure about the ones between Forward Battery and Control. Like you, I do believe that the After Battery hatch was ‘blown’ from the inside. If the hatch trunks on Grunion were the same as the ones I’m familiar with, the stainless steel trunk liner covered the entire inside trunk surface. It would take considerable force to separate and deform the liner.
    IF there was a circular run, Grunion knew about it, and would immediately maneuver to avoid and sound the collision alarm. I can easily recall how fast doors and bulkhead flappers got closed when that alarm was sounded! I think it’s fairly safe to say, that IF that is what happened with Grunion, all the watertight doors and bulkhead flappers were closed.

    One general question has been on my mind, and its answer could give some hints on the sequence of damage. At what depth did Grunion strike bottom and start its’ slide down the slope? Above hydrostatic collapse depth, or below? According to Rear Admiral Andrew McKee “All the model tests indicated Grouper” (SS-214) “would fail at 550 feet at the deepest”. Although some skippers of Gatos reported going deeper than that, it is a ‘starting point’.

    October 7, 2007 | 7:07 am

    Speaking of low pressure bubbles, here’s an idea that Jethro didn’t cover; If the control room/AB bulkheads collapsed/imploded violently, and vented via the AB hatch…could this account for the dished/”pinched in” bow? The weakened plating getting “sucked” into the remains of the Forward torpedo room/FB compartment?

    October 7, 2007 | 8:02 pm

    A couple of e-mails exchanged with Bruce and some of the last posts have convinced me that the AB hatch was blown open during the boat´s implosion. It seems that we all agree by now that the sinking was caused by an explosion in the FTR.

    But Bob´s last paragraph in his last post is most puzzling, and regarding the boat´s “attitude” when hitting the bottom I think that Ed Walson´s post about shiftin Center of Gravity deserves a much closer view. If someone has Naval Engineering qualifications, and the stability crossed curves for this class of sub, we might figure out where the COG was after the FTR was blown apart. But we must remember that at the same time water rushed into the forward part of the boat, in part compensating the COG some distance forward again.
    Furthermore, the stern compartments are imploded, which means they were still dry so this section was light in comparison.

    Now allow me to relate the assumption of a light stern to the “pinched bow” effect.

    We have assumed the FTR was severed from the rest of the hull by an explosion, but what if not? I recall the story of a sub that fired twelve torpedoes at an oiler, all of which hit but none of which exploded. The skipper observed in every case a spout of water. This was caused by the compressed air tank of the torpedoes exploding. Could this have been the case on Grunnion? Where there any oil tanks around the FTR that would account for the “black water” even if the torpedo didn´t explode?

    If you think this might be possible, then we have a bow heavy submarine with an uncontrolable flood. On its way to the bottom it passes crushing depth, bulkheads collapse and a hatch is blown open. The damaged bow hits the bottom and bends upwards. If you do this with a tube of paper you´ll see creases appear where the material is compressed. If this happend to Grunnion´s hull, this resistance failure coupled wiht external pressure would bend the steel inwards. Except in the bottom, near the keel, where the steel would not be compressed but stressed. In the bow pictures the bottom doesn´t look pinched (as far as I can see, but me eyesight is not that good).

    Contrary to the dead stop Ed described (as in this scenario we don´t have an explosion) Grunnion still has a forward motion, either by inertia from her lost propulsion or by her free fall to the bottom. With her bow burried in the mud, the hull breaks where the creaes appeared and finally lands on the silt (bending the rudder, that´s clearly a bend caused by an upward, not lateral force), sliding down to its present position.

    I think when this thing happens (a haevy body sliding down a slope made of soft material) a small landslide occurs, so the marks along the path are not made by the hull, but are scars left by portions of the bottom when moving downslope. Can someone check Robert Ballard´s book on the finding of the Bismarck? If I recall well he describes this phenomenon in it.

    I´m sure this reasoning has some weak point or another, but at least it´s new and may spark a few ideas. I´ll be more than glad to hear your comments.

    October 8, 2007 | 1:46 am

    Bob, I think there´s a simple answer to your question, wether Grunion hit stern or bow first.

    The main question we´re trying to answer here is: why did Grunion sank? If you ask people like us you´ll get answers like the ones we´re proposing. But ask a naval engineer and he´ll say: Archimedes! It sank because it´s weight was greater than the lift provided by the water it displaced. In other words, ships float or sink as the result of interaction between two forces: weiight and lift. In our particular case:

    The stern compartmets are imploded, so they were dry and rushing water had no access to them until the implosion.

    Whether the FTR was still attached to the hull or not is irrelevant. Although the Center of Gravity would have shifted aft in case the fore end had been severed (as Ed Walson correctly points out) that´s only one of the forces involved. What happened with lift? Just as the COG is the point were weight is applied, there is a point were the lift is applied: the center of buyoancy. In a surface vessel, any distance between the two centers in the longitudinal way will produce a trim, with which the COB changes until it is aligned with the COG. Submerged submarines, however, have no longitudinal stability, no change in trim will produce a change in the postion of the COB. That is why fore-at personell movements are restricted and when they occur the diving officer has to compensate them.

    When the forward compartments were flooded this center of buoyancy moved aft, to the dry compartments that were the only parts of the submarine still providing some displacement and lift. Imagine a cutaway drawing of the boat, paint the flooded compartments blue and the COB must be near the center of the white (dry) compartments, well towards the stern. The COG, however, could not have travelled so far. even if it had gone into the forward engine room. The final result is a lift force applied further aft than the weight, and that means a down bubble.

    Ed Walson
    October 8, 2007 | 7:35 am

    Guido, From rusty memory…the COG (Gravity) and COB (Buoyancy) on SURFACED Gato boats were about 16 foot different (perpendicular) and centered on Control Room, which Engineering-wise also was the center of NEGATIVE TANK (an important tank). In fact I would guess that negative tank was located at this point for this reason. ie; Flooding negative tank would simply take to boat down, with-out otherwise upsetting the Formal Trim.

    This is a principle that all ‘proper’ ships have: ie; COB is above COG at all times, distance between POINTS depending on vessel burden. During Diving or Submerging of any submarine (which are not proper ships) the COG and COB change places. The two POINTS change places vertically, and when the two points are at the same (or pass the same) elevation the vessel is extremely unstable. ie. A large wave at this ‘moment’ could cause a large Pitch or Roll or both. Not likely, but this ‘physical point’ is a very real moment in time and has assocciated RISK. This is why Diesel Boats in-general rode-out big storms on the surface rather than submerged. There was/is a certain hazard to the Surface-Surface-Surface evolution.

    Grunion during this attack was at Battle Stations, ie: all Water Tight Doors were closed and dogged (maybe not all ventilation ducts and their flappers). She had a GOG, but it was very dynamic. There are provisions in fthe sequence of firing a 3,000 lbs. torpedo wherein the weight of the explused torpedo is compensated for by taking-in (retention of) the sea-water which displaced the volume of the fired torpedo…but it is not weight perfect. The Diving Officer and Trim Manfold Operator have to ‘pump and flood’ additional water into-out-of the Trim Tanks in order to fully compensate to a ‘FINE’ Trim. This is a time consuming activity due to the pumping rate (GPM) of the trim pum + over coming sea pressure. The Diving Officer probably started the attack at a ‘Negative Buoyancy’ (of +1,000 lbs. or so overall) so that in effect, the forward motion of the boat, with water flowing over the bow and stern planes, tended to ‘hold’ the boat at periscope depth.This is the only ‘LIFT’ inherent in a submerged submaine. This trim would was a common practice (depending or sea conditions) and helped to prevent to biggest NO-NO of all, which is ‘Broach’ of the sail or shears.

    So…POB is several feet below the keel (Grunion at this point is not a proper SHIP and has zero buoyancy or less). POG (simple balance) is not Fine Trim, but Compromised Trim (work in progress-due to 6 x 3,000 lb. Torpedos expended in 20 minutes & and a hard turn for course correction). Explosion at Forward Torpedo Room…Grunion losses several thousand pounds of weight from bow balance component more or less instantaniously. This causes a large ‘UP’ bubble, from which she never recovers.

    The unflooded compartments at this point provide some displacement of weight, but this displacement is not siqnificant compared to over all weight and distribution.

    A factor in this scenario is the remaining fuel oil. Assuming a ‘settled’ angle of something in the order near perpendicular (180 degree), not all of the fuel is lost from the ‘free flooding’ FBT fuel ballast tanks. Diecil fuel is roughly 80% of specific gravity of seawater, and remaining fuel in otherwise undamaged FBT would have effected the overall keel angle (and velocity) of the boat during descent.

    The ‘big black brown bubble arose’ eye witness account: the colors are inherent in the chemistry of the exposive.

    Archimedies (287 BC) is the Patron Saint of Submariners and Divers as he originated all of the volume and surface area ‘numbers’ used by ComSubPac to solve these type of questions.

    I have some comments reserved for COMSUBPAC which I will post later.


    October 8, 2007 | 7:00 pm

    Of possible bearing on the discussion, and for what it’s worth, from Jethro’s “Internet School of Photo Analysis” (Dave, shame on you for neglecting your edication);

    (1) What appears to be “recent” wreckage from the continuing collapse of the conning tower is lying to the port (as should be given wrecks orientation).

    (2) What appears to be the bridge cowling (portholes) and ladders lying across the center/starboard side of the conning tower, BEHIND the periscope shears, to the starboard. This can be seen most clearly without enhancement in pic “Open hatch 22”. Cowling is “face downward” with l(what appears to be) adders etc. on top of it. NOTE: GRUNION is lying head down with an incline to port.

    (3) What appears to be the RDF mast has fallen forward across this wreckage (possible fishing net/line tangled in top?).

    (4) What appears to be a glass port from the bridge cowling is lying on the deck adjacent to the AB hatch.

    (5) What appears to be wreckage from the conning tower (from the size and the attached mounting braces) is also tangled with the deck gun base (pics are really bad, but my best WAG is part of it is plating from the shears).

    (6) The deck gun is angled astern, and is at full elevation. What kind of force (and/or orientation) would required to break the travel lock and pitch the barrel into this position?

    (7) Periscope shears are bent moderately to the forward and port. Bend increases toward the top. Currently appear to be separating from the conning tower and are going to collapse forward/port. “Original” bend doesn’t appear to be from deterioration of the wreck.

    Bow; Looking at the pics (I’ve been concentrating aft), it appears the bow separated from the bottom upward and went over the upper port quarter. This would account for the (few) jagged metal edges angled upward/port, dished plating on the starboard edges, and even more pronounced dishing to the port, i.e. the “squished paper towel roll” effect. You can actually see on the starboard edges where the metal was “stretched”. It doesn’t appear that this was the actual point of impact/explosion because of the relatively “clean” edges, but where the weakened hull failed, possibly because the hull was more rigid at this point (due to the escape trunk mounting?). The actual point of explosion appears to have been low on the port quarter (pushed in plating), somewhere forward of the break. If you examine the pics of the break closely, the hull has been pushed upward and starboard from this point, and deformed inward. I think this is independent of the bow section separating.

    If GRUNION had an explosion/torp hit forward, weakening the hull (obviously) at this point, what would be the effect (on the damaged bow) of her forward speed, attitude, bow plane orientation, and the weight forward, given what details we know?

    To summarize;

    (1) I don’t think the hull forward of the break “vaporized” or fell off immediately. I think it got corkscrewed off relatively quickly, in the descent, or less likely, on impact. I’d specuate that not only did the GRUNION suffer a circular run, but possibly had one of the few instances where the magnetic exploder worked (more or less) as advertised.

    October 8, 2007 | 10:03 pm

    First I´must appoligize if I sounded too self-confident in any of the paragraphs of my previous post. Second, I am also a submariner, so I know all the stability problems associated with diving and firing torpedoes. But as I am not American and Spanish being my mother language, I may have used the wrong words to describe the “lift” of a ship. I believe you are speaking about the “dynamic lift” provided by the diving planes, while I was speaking about the “static lift” provided by the water displaced by the submarine´s volume.

    What I meant for “lift” is the force resulting from the weight of the water displaced by the hull. The point where this force is applied is always, if I´m right, somewhere within the submerged portion of the hull. If a surface ship alters its trim the shape of the submerged hull changes and so the position of the COB shifts. In a submerged submarine whichever the bubble is, the shape of the submerged hull doesn´t change so the COB remains stationary. Even when a submerged submarine has near zero bouyancy, this means that there is a force almost equal to the sub´s weight applied in the opposite direction, and its point of application must be somewhere in the hull, otherewise the said force would have no effect in it and it would sink.

    However, if Grunnion´s bow was severed the shape of the hull did change and so did the position of the COB, which moved aft. At the same time, there was a loss of weight at the bow, which made the COG travel aft too, how far we would need an engineer to make the calculations. From the pictures I hope you´ll agree with me that the aftermost compartments are collapsed, whereas the forward ones are not (except for the conning tower). This would mean that the flooded portion of the forward part of what remained of the hull was providing only weight, not compensated by any significant displacement of water (only the thickness of the steel plates would displace any). That is why I am convinced that Grunion sank bow first (or at least must have hit the bottom in this position).

    Regarding the “black water” I was only speculating here. I have seen the explosion of a torpedo running at 25ft with an equivalent explosive charge of 460kg (920lbs) of TNT and the black water rose to at least 150ft. That´s why I wanted to propose the “dud torpedo” scenario, I thought that such a geiser would have been described more accurately by the witnesses, that´s all. And I also would have expected such an explosion to have blown open the FTR watertight door and allowed for the flooding of the control room at least.

    But I believe you may be remebering something wrong. During diving process, COG goes down as a result of the ballast water filling the tanks from below, and at the same time the COB goes up as a result of a larger portion of the hull being submerged (the subs I´m used to have only fore and aft tanks, not saddle ones, but I´m almost sure it must work in the same way). “Free surface” effect while the ballast tanks are partially filled further decrese this difference in height between the two points. This effect dissapears when the tanks are completely full. But the points never change postions. COB remains always above COG. Just picture the cross section of the sub with both points and a string attached to each: pull downwards from COG´s string and upwards from COB´s. If COG is above COB, the opposed forces will turn the sub upside down, until the nullify each other. On the contrary, if COB is above COG the submarine will always right itself. Unlike surface ships, submerged submarines have a stability range of 180°, they would always end upright.

    It would be most interesting if someone could make the calculations required to determine how far bach did the COG and the COB travelled. Hopefully the data required will be somewhere among the mass of plans that apparently are available.

    October 9, 2007 | 8:26 pm

    Speaking of over-confidence; I’ve started to take a close look at the pics of the forward section of GRUNION.

    I’m now pretty sure (but not confident) the Forward Battery compartment imploded. Violently, as per the center line compression described previously by Ed. The effect is much more pronounced/noticable in the after compartments, likely because the hull (and compartments) were much narrower.

    I think the bulkhead between the Forward Battery room and the Forward Torpedo room is either gone, or flattened forward almost to the escape trunk, to include the reloading hatch…the available pics don’t show that area well. But it appears to be choked solid with debris. I haven’t been able to ID the top of the FB compartment at all, or ID any of the debris other than some of the deck fittings and sub-deck piping. The “compression damage” stops at the break of the conning tower, more or less where the FBR/CR bulkhead was located.

    I’ll take a rain check (for once) on rushing to any conclusions…

    Ed Walson
    October 13, 2007 | 1:49 am

    In response to David’s observation that maybe Aiura used the term ‘Stem’ correctly and meant ‘Bow’ as regards the last three torpedoes. The question was ‘If the spread was aft to forward’. I looked at that with even more rusty Trig ability. The problem is ‘Target Forward Speed’. This input to the TDC is basic to the TDC’s recommended Gyro Angle for Torpedo Course. I am purely guessing that it can accept a target forward speed of something between maybe 40 knots down to 0 knots but it needs to be a positive number (assume zero to be positive). This kept me awake for two nights and in the end I still don’t know how or why Fire Control Tracking Party would (or could) set up a spread from stern to bow. I think they would do it the same way they always did it, nothing new under those conditions.

    However I plotted it out and found that it certainly would be possible for that miserable
    6th torpedo to make a circular run to its left or port.

    Note: My accumulated information on MK 16 Exploder mechanical enable range is several references to 450 yards and one reference to 450 rotations of the impeller wheel. Assume one rotation is one yard of travel? I no longer even consider that Grunion was too close when they fired. Practically impossible. The 4th and 5th torpedoes were duds. In my plots I assumed a minimum track of 500 yards.

    I assumed Kano Maru to be 200 yards long. Spread was fired at 10-15 second intervals with gyro angle 4 degree between shots at the target (this allows approx 50 yards apart at impact). Torpedo 4th and 5th impacted more or less where they were aimed.

    If Torpedo 6th ran circular to its Right it was appox 11 degrees off target at 500 yards, passing 50 yards astern of Kanu Maru.

    If Torpedo 6th ran circular to its Left it was approx 22 degrees off target at 500 yards and passed 50 yards to STEM (bow) of Kanu Maru.

    A perfect circle (in the case of the Left circular run) from the firing point (intersected approx 50 yards astern of target) worked out (not surprisingly) to be 1000 yards in diameter and 3,140 yards in Circumference. Torpedo run time at 47 knots 1.98 minutes or 1::58 secs.

    I still like the idea (David’s post of 4 Oct. noted “possibility…there were fish remaining aft” ) that this was a stern shot. What happens next is possible in the two minute time frame.

    Note: I don’t think Grunion was aware of the circular run, they would have flooded negative and went deep.

    If this was a Stern Shot, Grunion (according to the general sketch from Aiura) and Grunion was more or less stern-on to the target (at 147 degree heading, at guesstimated speed of 3 knots, she turned hard to port and came to approx 050 degree compass. (A course change of something like 100 degrees) I don’t know what Grunion turn radius was but in 2 minutes at 3 knots she travels over 200 yards square into the perfect circle.

    Note: There is a pretty good case for Bob’s comment on 8 Oct. that “the magnetic exploder worked (more or less) as advertised”. Thats my work-in-progress.

    I noted two other places in Aiura’s Narrative that he used the term ‘Stem’.

    (1) ‘saw two torpedo wake overlapped at 100 meter starboard fore’ ‘crossing 45 degree with us’. He takes evasive action of starboard rudder and the ship responds (coming more parrelell with the torpedo wake). (2) “one torpedo passed after the STEM, we could avoid it…but other one hit machine room starboard”.

    I think he clearly meant STERN here but a couple of other questions are raised. It takes MK 14 at high speed (47 knots) about 4 seconds to cover the distance. Clearly not time enough to make rudder movements. If the figure here were 1000 yards the time increases to to about 38 seconds, which at his probable speed of 15 knots may have been time to alter his course to actually avoid the aftermost torpedo.

    However the comment ‘torpedo wake overlapped’ make me wonder if the 1st torpedo fired that morning wasn’t also trying to run to left of target. Almost like ‘so whats new?.

    (2) After the 3rd Torpedo fired from Starboard 157 angle on the bow (the single shot which ran deep) Aiura’s statement “the periscope sometimes appeared and moved from the STEM to portside”. The sketch indicates that Grunion passed astern of the target to the port side for the final set-up. I think he meant stern here or the interpreter simply got it wrong.

    So while the starting numbers are wild, when this is drawn out it fits together pretty neatly.

    David Decrevel
    October 14, 2007 | 5:27 pm

    Ed, sorry to have cost you 2 nights sleep with my WAG, but look at the bright side, you got to use your rusty mathematics again. Bob was correct in chiding my neglecting my education, but I did graduate first in my class in Jethro’s “School of Wild A** Guesses”.

    Speaking of mathematics, John Hart and I were talking and he suggested I do a ‘plot’ to ‘guesstimate’ Grunion’s movements. I came up with some things that matched what you say regarding the first shots. Working from the charts and diagrams by Aiura, and using the usual submarine plotting tools commonly found around the house, I came up with the following: (partial excerpts)

    Kano Maru Speed Estimate:

    Working from Aiura’s ‘chart’ drawing, I estimate the position at 0515 to be 52 deg 9′ 25″ N, 178 deg 5′ 25″ E. At what I assume is the 0547 position (circle in center of circle) estimated position is 52 deg 07′ 20″ N, 177 deg 52′ 15″ E. From the 0515 position the extreme northeastern tip of Segula Island bears 158T, at 7.66 nautical miles. Course from 0515 position to 0547 position is 255T. Distance from 0515 position to 0547 position is 8.34 nautical miles estimated. The distance traveled in 32 minutes makes the speed 14.36 knots. If I do the plot using the 0515 position and the 0544 position, estimated to be 52 deg 07′ 10″ N, 177 deg 53′ 45″ E, the distance traveled from 0515 to 0544 is 7.53 nautical miles on a course of 252T, in 29 minutes, for a estimated speed of 15.579 knots. The estimate of distance between 0544 and 0547 positions is approximately .81 nautical miles. At 15.5 knots one could go exactly .81 nautical miles in 3 minutes.

    First Salvo:

    At 0547, Kano Maru, on a course of 255T, sighted torpedoes at 100 m, coming in at 045 relative, or from approximately 300 degrees T. Mathematically, at a high-speed setting of 46 knots, the torpedo would take only 4.23 seconds to run 100 meters. At a low speed setting of 31.5 knots it would take only 6.179 seconds to run 100 meters. If observation is correct as to distance (100m), then Kano Maru had insufficient time to execute a turn, and one torpedo simply ‘missed’ aft. If the distance observation is incorrect, or mistranslated, and Kano Maru avoided one torpedo by turning, she could have turned no more than approximately 35 degrees to about 290T in order for one fish to miss aft and a second to strike, probably aft of amidships. (The exact location of the ‘machinery room starboard’ unknown, but from Aiura’s drawing it is indicated aft of amidships). Any turn further than about 35 degrees would have likely made the 2nd fish miss astern as well. This is, of course, dependent on Kano Maru’s actual speed, and rate of turn.

    As you note Ed, one fish of the first salvo might also have been ‘erratic’. Comes down to exactly what Aiura meant by ‘overlapped’ I suppose. For the purposes of my plot I estimated Kano Maru to be a length of 443’ (Katsuragi Maru Class), and I used a shooting range for Grunion of 800 yards.

    This obviously brings us no closer to what actually caused Grunion’s demise, but like Ed, it exercised my rusty mathematics skills.

    David Decrevel
    October 14, 2007 | 5:50 pm

    With continuing research through various sources I have found these reports of circular run MK 14 torpedoes, including the two previously mentioned.

    11 April 1942 Seadragon SS-194
    “At 1720, she fired three torpedoes. Twenty-nine seconds later the first torpedo exploded halfway to the target. The second torpedo broached and circled abeam of the target. The destroyer avoided the third torpedo. Seadragon changed course and went to 200 feet to avoid the circling torpedo and the expected depth charging.”

    7 March 1943 Triton SS-201
    “One of her torpedoes made a circular run which forced her to go deep.”

    23 March 1943 Whale SS-239
    “Whale fired a fourth torpedo which ran “hot, straight and normal”—for one minute, then circled, heading back in the direction of Whale. “We went to 120 feet and prayed”, the commanding officer later reported. The erratic torpedo changed its mind after reaching Whale’s beam and headed back for the freighter, finally exploding.”

    9 June 1945 Tinosa SS-283
    “Sound reports torpedo making circular run! Can hear screws plainly as torpedo, set at six feet in depth, passes close overhead with screaming whine. FLOOD NEGATIVE! TAKE HER DEEP.” (I can’t ascertain if this particular event was a MK14 or MK18.)

    October 14, 2007 | 8:54 pm


    I´m sorry to admit that I can understand little of your technical description of a spread firing, but if what I understood (regarding the 3rd salvo and positive speed imput for the TDC) I must agree with you that there´s no reason for the Fire Control Tracking Party to do anything different than usual. The only possiblity would be that the CO mistappreciated the Target´s Angle on the Bow by 180°, something uthinkable of in this case.

    Just as evreybody here I believe in a circular run, at leat there´s no photographic evidence of a shell hit anywhere (unless it hit the bridge,which is missing, but in that case it didn´t compromise any part of the pressure hull and so played no part in the sinking) and I have read with great interest your posts about your “manual simulation” of the torpedo tracks. Out of sheer ignorance about Mk14s I´d like to ask you a couple of questions:

    Was there any “straight run” right after the torpedo was launched and before the exploder was armed? (modern ones have it, it´s intended to keep them from homing in the sub´s own noise)

    I believe you´ve done your simulations with the fast speed setting, would that be the most likely speed chosen against a stationary target?

    If you think the answers are a little off this blog´s aim please feel free to contact me at

    And now a couple of questions for the audience in general:

    Are there any records about the changes of speed and course after the torpedoes were fired in Wahoo and Tang? Maybe if they could be examined they could shed some lignt on this case.

    And the BIG ONE (for me at least, if it´s been ansered before please forgive me):

    There were two torpedoes fired in the first attack: one hit and exploded, one missed and should have sunk at the end of run.

    One torpedo on the second attack which ran deep, missed and should have sunk at the end of run.

    Three torpedoes in the third and last attack, two hit and were duds, third missed and possibly hit Grunion.

    That gives a total of two duds, two missed and sunk, and (possibly) two hits: six in all.

    But Kenji Hamada clearly states that he observed FOUR torpedo bodies floating: two would be those of the last two duds, they were even close to each other as one would expect of two things that stopped at about the same place. But where on earth did the other two come from?

    In the first place I doubt that the body of an exploded torpedo would survive and even less in a floating condition. But even if you grant that, what are the chances of the first hit and the last torpedo bodies float side by side after 20mins action?

    Could there have been more than six torpedos fired? Could any dud have gone unobserved in the excitment of the moment?

    I hope I won´t keep anybody awake with this.

    Ed Walson
    October 15, 2007 | 1:58 am

    Guido, With MK 11 Mod 3 there was no straight run to distance the weapon from firing vessel. It may have run relatively straight untill the steam turbine got up to full RPM and the gyro scope got up to very high RPM. Steering engines were powered by High Pressure air flask. Rudder controls were influenced by turbine RPM for the gyro position sensing mechanism somehow (I think). MK 6 exploder was (my mis-use of the term ENABLE) fully armed at a through water travel distance of approx 450 yards by rotation of an impeller wheel located in bottom of war head (in the exploder cavity). This wheel required to rotate 481 revolutions (approx 450 yards ?) which mechanically raised the thumb sized, very high explosive ‘initiator’ up and into the cavity of coffee cup shape and sized ‘tetryl booster’ which was inside the HBX war head. The spinning impeller also charged the electical capacitor which provided the electrical charge neccessary IF all other conditions allowed a dentonation.

    My quick and dirty looks at firing geometry didn’t look at different speeds as direction and possible turning radius were my objective. However, I think they would have all been hi speed shots because slower speed would give the target more time for evasive action, which Kanu Maru may have actually accomplished at the first action.

    Kenji Hamada, Contract Newspaperman saw torpedos #4 and #5 in two different places, while his small boat traveled around the Kanu Maru. The expanded torpedos with 630 lbs war heads broken off and steam engines now flooded would float in this attitude because the High Pressure air flask was in the main body of the topedo housing to supply buoyancy.

    Ed Walson
    October 15, 2007 | 2:27 am

    David, I’ll show you mine if you’ll show me yours. Contact me and I’ll send PDF of my scratch pads. You may try to see if you can tinker with Grunion position and turning circle given the choice of bow or stern firing position for the last salvo. My rough sketch answers OK for a stern shot and a 110* turn to port but gets more complex for a bow shot. Laying it out in plot with estimated Grunion speed and known length should be a piece of cake.

    I assumed Kano Maru at 15 knots on the morning because of his mention of that speed two or three days earlier when he lost his escort and was headed back out to deep water in the fog. I figured that after he got his morning star shot and knew where he actually was (first time in three or four days) that he headed for the barn as fast and directly as possible. I think his signalmans first observation (shots #1 & #2) must have been at 1000 yards.

    I think his various reported estimates of distance over water are off (short) by at least 30%. The Grunion did not fire #3 or #4-#5-#6 from outside of exploder arming range (450 yards). When I did my rough calcs and boat positions his reported 8 CM shell (angle-direction from his sketch) surprised me with an intersection on my estimated possible Grunion position and scaled out at 600 yards not reported estimate of 400 yards and this intersection was based on Grunion firing the last rounds at 500 yards. I think even 500 yards is too close but then I only stay at the Holiday Inn sometimes.

    October 15, 2007 | 1:09 pm

    I just noticed the hypothesis of the sinking located at

    A few comments; I think it’s highly unlikely that water pressure stripped the remaining foward decking and took the forward fairwater/bridge structure plating with it. The fairwater is designed to be “free flowing”, and more than one boat came home with sections of the decking stripped. The (some of the) main deck supports can be seen in the debris atop the the FB compartment, as well as what appears to be the (bent) forward radio mast and associated fittings. In this scenario, these would have been amongst the first things carried away…long before the fairwater. Yet they are still (more or less) where they should be. If I had to guess, my money would be that something fairly substantial struck the bridge, demolishing it and bending the shears in the process. Most likely the bow or debris from the bow when it separated.

    Speaking of the shears, and “black rods falling over”…where’s the attack scope? The search scope is shown housed, but the attack scope isn’t shown in any of the pics (that I’ve seen). Whether it’s housed, snapped off, or still extended could be a useful fact.

    Also, the deck gun is most definitely reasonably upright, pointing at max elevation, and located where it should be. Canted somewhat rearward to the bow, but this is because of the distortion/break to the hull. The gun is mounted roughly over the AB room/forward engine room bulkhead, and is mounted to a fairly substantial reinforced platform fixed to the main hull IIRC…the bulkhead areas have (reasonably) kept their original form. Photo “2nd sighting port side 26” shows this fairly clearly, without examining the other photos. However, if you look at the other pics showing detail, you can clearly see that the elevation gear/cog is all the way forward. Compare against the pics found here;

    One theory to consider; The damaged bow and flooded forward torpedo room (if still attached) would have put GRUNION into a steep head down attitude during initial decent. Once it separated, losing the weight forward, the GRUNION corrected somewhat to a more “keel down” orientation, but still in an uncontrollable “dive”. Given the extremely steep slope of the bottom, struck stern first, then pogoed forward, impacting onto her starboard bow. Finally settling with weight to the stern, and slid down the slope. Something for everyone…lateral damage to the rudder, dishing in the starboard bow (but not crushing it), compression/impact cracks to the hull forward and aft, the “undamaged” front of MB#1 etc.


    “Was there any “straight run” right after the torpedo was launched”

    I think after the torpedo is fired there was a straight run called the “reach”, before the gyro angle kicked in and put it on track to the target.

    October 15, 2007 | 4:11 pm


    I don´t think that the 100m distance is correct, either by missappreciation or by incorrect translation. Imagine yourself as the Captain on a day with visibility reduced by fog when suddenly someone cries out “Torpedo”. You spend 1 sec trying to figure out if you heard correctly, then why me, another second looking out to see by yourself, a third shouting an order to the helmsman who instantaneously obeys you, and that leaves only one second for the rudder to move and for the ship to start turning. Impossible.

    On the other hand 1000m seems to me too far away (especially if you´re assuming a firing distance of 800yds), you would need to be quite high above the waterline to see the wakes at that distance. Don´t know what the bridge height was in KANO MARU.

    I believe the first torpedo just missed aft. The overlapping wakes indicate an erratic run, but Aiura doesn´t say if he was hit by the straight wake or the overlapping one. It is possible at this stage (first attack) that Cdr. Abele misscalculated the target´s speed. You used 15.5 knots in your calculations, any skipper with a good sailor´s eye would go either for 15 or 16, and that would be enough for a close miss. If the speed chosen was 15, then the torpedoes would have missed astern, unless one of them ran erratically and had a small deviation to the right. That one would hit.

    About the torpedo speed setting we would need to know what where the “default” settings for this type of target, probably there was a CO manual that would have been hammered into every CO´s brain during his training. War was only six months old and probably not enough experience had been yet obtained to allow skippers to deviate from their training proceedures without facing severe reprimand on return.

    And t

    October 15, 2007 | 4:22 pm

    David, just found this on Google:

    Kano Maru, length between perpendiculars 137m (about 425ft) 6940 t, 17knots cruising speed, 18.7 max. Are you figuring out her speed from “fixes” on a chart? That would give you “speed over ground” or true speed, but not speed over water, and that would be the one used for the fiiring control solution.

    Do you have information on the currents and the wind condition at the time of the attack. The positions of the two pairs of torpedo bodies I don´t think it is possible they are the same, they couldn´t have drifted 1100yds (or any distance, actually) form bow to stern faster than the boat form which Hamada sighted them.

    October 15, 2007 | 5:55 pm

    Thanks for the explanation on the workings of the exploder and it´s arming process.

    Regarding the torpedo´s speed, different speeds will yield different turning radiuses, just as they do for ships. Maybe it´s worth trying them and see what comes up. Most surely the first salvo was set at high speed but once the target had been disabled there was no need for this.

    About Kenji Hamada´s sightings, they keep puzzling me. At first I thought they were the same pair sighted twice, but then I thought why would they drift in a different way than KANO MARU? They shouldn´t have changed relative positions, unless there was some significant wind that made KANO MARU drift more than the torpedoes: they would drift with the current alone.

    But furthermore, if Kenji saw them first off the bows and then off the stern, what means that they had drifted to that position faster than his boat, for they were already there for him to spot when he arrived. He says he saw “same two objects”, but then again, there would be no exterior differences with which to identify them, especially when he says that he saw the first pair at about 200m and couldn´t approach. I think I´ll try my cinematics and see what I can figure out.

    Unfortunately (for our particular interest) KANO MARU was sunk a few days later by air attack so it was never docked, and we´ll never know how many torpedo warheads she had in her belly.

    October 15, 2007 | 10:41 pm

    If this helps your attack plots;

    KANO MARU is listed (has her own entry) in the USN 1942 Recognition Manual (O.N.I. 208-J), (which GRUNION would have had) with stats that agree with those listed in Lloyds. Includes pictures, a diagram, and mast/kingpost heights.

    Engines amidships, and appears to have 3 hatch covers forward, 3 aft.

    Tonnage; (gross) 8572 / (D.W.) 9731
    Length; (wl) 454′ / (oa) 477′
    Beam; 61′
    Draft; (loaded) 28′ / (light) 11 1/2′
    Normal Cruising; 16 knots
    Maximum; 19 knots / 106 RPM @ 16 knots

    Cargo at time of contact;
    Coal (unknown amount), Cold weather clothing (unknown amount), 1 x Jake floatplane, 1 x Rufe (or possibly a Pete) floatplane, 1000 cubic meters of general construction materials, 4 x Diahatsu landing craft/barges, 5 passengers

    David Decrevel
    October 15, 2007 | 11:50 pm

    Guido. I don’t know whether the 100m is correct or not, which is why I figured my plot based on both possibilities. My conclusion was, if distance is correct, Kano Maru didn’t have time to turn to avoid the fish; if incorrect, she may have had time.
    For my purpose I was assuming both fish were ‘hot, straight, and normal’. To me, the ‘overlapped’ observation could be based on the angle from which they were viewed, or one fish may have been running deeper so the wakes made them appear overlapped, or it could indeed have been an ‘erratic run’. If we are to believe Aiura’s drawing that the first fish fired hit, and the second fired missed astern, it would have the 2nd torpedo running behind (outboard) the first fish, thus making them look overlapped. He was, after all, viewing torpedo wakes, not the torpedoes themselves. We are trying to make guesses based on Aiura’s verbiage and the translation of such, so it becomes another part of the guessing game.

    My purpose was to plot an estimate of just how far Kano Maru could have turned to avoid 1 fish, yet get struck by another. By that determination, and the subsequent sighting of the periscope, it can give us a clue as to a rough position for Grunion when she fired the first salvo. As is blatantly obvious, with a lack of so many ‘facts’, much of the ‘plotting’ is strictly conjecture. We know virtually nothing about Grunion’s actions except for positions where her periscope was observed, the direction her torpedoes were coming from, and the likely number of fish she fired. We have no way of knowing where Grunion actually was when she first sighted Kano Maru; what her position was when she fired; what range she fired from; what gyro angle she used; what speed, angle on the bow, range, and ship length she was using for Kano Maru; what speed setting was used, and on and on My plotting exercise was to try to determine if the positions where Grunion’s periscope was observed, and from where the torpedoes were observed coming from, were positions Grunion was likely to be at, and if she had sufficient time to get to the next position, set-up, and fire. My question was one of timing. I figured a ‘best case’ scenario for all the salvos; all bow torpedoes, straight shots set at zero gyro, a reasonable range of 800 yards, and a high-speed setting. Using those nearly ideal numbers I could show that it was possible for Grunion to get into the positions in the time indicated. Therefore, it is possible that she could get into these locations and fire with a ‘less than ideal’ setup. It also showed that there was sufficient time for Grunion to swing and bring stern tubes to bear for the third salvo if she did have fish left in the after room, and had chosen that course of action. Naturally I made a ton of assumptions.

    To add even more uncertainty to any plotting, there are things we don’t know about Kano Maru as well; how quickly her helmsman responded to the order; how quickly the rudder answered the helmsman’s input; what her rate of turn was; how far she continued after loss of propulsion and at what speed; how far she drifted when she came to a stop, and in what direction she did drift. Any plotting exercise based on the few things we ‘know’, is definitely a guess at best.

    By making an estimated position plot and by trying to calculate a speed estimate for Kano Maru, I was merely testing the translation accuracy, and to see if the observations and statements of Aiura were reasonable and probable. Naturally the speed estimate was figured on ‘speed over ground’ as determined from positions on the chart, as I have no clue of currents and drift, wind and waves, nor a clear picture of Kano Maru’s knot meter. I was not trying to determine a ‘firing solution’ for Grunion, just plotting from a navigation and timing perspective. Ed, in my mind, is much more qualified to postulate ‘firing solutions’ than I. My battle station was part of the fire control party in the conning tower, but at the ‘plotting table’ not at the TDC or in one of the torpedo rooms, and I’ve never stayed at a Holiday Inn Express.

    As to misjudged speed, it is entirely possible for a skipper to under/over estimate target speed, which often happened during the war, so a ‘miss’ caused by misjudged speed is not at all unusual. Nor is a miss from misjudged ship length, range, or angle on the bow. Firing a spread could make up for such errors, but as you correctly say Guido, if Kano Maru’s speed was 15.5, a judgment of 15 or 16 could cause a miss.

    From all I have read, most of the torpedoes fired during the war were at a high-speed setting. The only thing I can really see that is gained by a low-speed setting is greater range. Ed, as a Torpedoman, would be better equipped to answer that than I.

    Ed Walson
    October 16, 2007 | 9:37 pm

    David and All, Here are my thoughts on Grunion movements.

    At 0440 the fog lifts enough for Aiura to get ‘astronomical observation’, this is the morning star-shot and requires an observable horizon plus visible stars. Sextant stuff. He now knows where he is.

    At 0547 Grunion shoots at him from submerged position. Visibility is good enough for periscope approach.

    Kiska ASW is not eating breakfast in down town restaurants. Escorts lost Kanu Maru a few days earlier due to the fog, they know he’s coming in. At first light they were probably underway to pick up the escort again, or were already outside lost in the same fog themselves.

    If Grunion can see, they would assume ASW can see.

    Grunion shoots from position #1. She cannot stay at position #1 (1) because the torpedo bubble trail leads directly to that location and (2) Kanu Maru smartly takes the ‘text book’ correct action and turns down-track of torpedoes to lessen his aspect and this also puts him on a potential collision course. (I think that did happen a couple of times during the war).

    So Grunion turns to her port and opens easterly at 110* (your plot). This course also is ‘getting out of here’ away from ASW at/or nearer Kiska (At this point Kanu may be sinking). Grunion does not know that the Kanu does not have battery back up on their radio and assumes the call for assistance went out at 0548 hours.

    Target does not sink. They decide to take another shot from Bow or Stern depending. The ten minute elapsed time between shots is enough to turn around and get a good set up for either end.

    0557 Takes single shot / run deep / clean miss / (The fact that this was a single shot indicates that which ever end Grunion was firing from has now unloaded tubes). This shot should have been the end of it.

    From Fire Point #2 to final Fire Point #3 is 250* which is also ‘getting out of here’ course. Puts Grunion just that much further away from ASW Kiska.

    Again the ten minutes elapsed from 0557 to 0607 is adequate time for a set up of choice, but none the less a full twenty minutes has elapsed. Grunion would assume the Cavalry was close aboard, nobody is wasting time. Note: This twenty minutes of fire control tracking party activity and hard maneuverings did not allow for reloading any torpedoes. Aside from the angle/dangle of chasing the bubble all over and other trim adjustments, I just don’t think there was manpower available for it.

    After the failures of final 3 x torpedoes I think Grunion decided on making a run out to the east again. This would be a ‘good get away from here’ course and allow her to go deep long enough to reload what ever was available and see what ASW activity took place.

    I consider #2 and #3 positions both good for stern shots all things considered, but not leisurely shots. In any event there was time for the turns necessary for bow set-ups.

    October 17, 2007 | 12:11 am


    I´m starting to feel like I´m a pain in the lower back here, saying what causes me doubts but making no “calculated” (as yours or as Ed´s) guesses, just speculations. Looks like I´m the devil´s advocate, but as long as you bear with me I´ll keep posting… anyway, I´ve also posted my e-mail address in a post for Ed, feel free to use it if you want.

    The fact of at what distance the torpedoes were seen is more or less not important. Aiura did have time to give an order and it was obeyed. If the ship had enouch time to start its turn before the hit or not doesn´t matter, the torpedo did hit.

    Now, and Ed may find this part interesting too, I´ve had some difficulty trying to picture some of Ed´s plots descriptions although I didn´t try to recreate them myself. I suppose he´s using relative bearings (measured from the bow, I don´t know the word in english) for Aiura uses these as well.

    As I have said in my previous post I´ve been puzzled by the two pairs of torpedo bodies floating upright: either there had been four duds or it was the same pair. I did some basic cinematics and concluded this: the pair sighted off the bows would correspond to the observed duds, so KANO MARU would have been drifting bacwards, probably due to wind. But if that was so, there´s no reason why that same pair should have appeard off the stern and on the other side maybe 20mins after that (even if Kenji Hamada had stopped to peep into the torpedo hole on the side – if ti was visible – it wouldn´t have taken him longer to steam aroung the ship). KANO MARU couldn´t have drifted backwards and then forward again. I saw a clue in that the estimated distance to the ship from both sightings is similar, and my guess is that it had simply turned around, probably due to a change in the wind.

    Now you´ve written something we all assumed, but just now I believe it may be important:

    “how quickly the rudder answered the helmsman’s input; what her rate of turn was; how far she continued after loss of propulsion and at what speed; ”

    Let´s assume that the rudder had time to travel to the “full rudder” position before the hit. Aiura said that after the torpedo had hit the ship was left without any type of energy (even the generator had stopped). If I´m not wrong, steering gear would have been either steam or electrically driven, and as this ship had a diesel I choose the second. But if there was no electricity, the rudder would have remained hard to starboad and the ship would still have a forward motion, and thus, it would have kept turning. None of this would be apparent on a “relative” plot, but it would be on a “true” one, which unfortunately is not the case with Aiura´s.

    So far you have proved that GRUNION could have been where and when she was spotted (even if you considered KANO MARU´s heading constant) so it would have been even easier for her to carry on the same attacks in the event that KANO MARU kept circling.

    And Ed´s calculations also seem to demonstrate that a circle runner has all the probability of having been the cause of GRUNION´s sinking.

    Does this change anything in your calculations? I don´t think so, but for what´s it´s woth here it is. Anyway, at least until we have more photos or info that may help us work out the actual cause of the sinking, the last posts seem to have turned to analysing GRUNION´s attack.


    Ed Walson
    October 17, 2007 | 12:27 am

    All, Part of this post is an answer specific to Bruce regarding Hydrostatic Damage

    My understanding: Hydrostatic Pressure is defined for our purposes as Water Pressure. Sea Pressure, regardless of depth, is applied equally to all exposed surfaces of any pressure vessel. Hydrostatic Damage would be when this pressure exceeds the ‘yield’ point of the fabrication material (steel) and the steel fails.

    An example is the Conning Tower. Sea Pressure was exerted equally all around the pressure vessel except on the Hatch and Trunking. Due to the exposed surface area (in square inches) of the Hatch the pressure exerted on the hatch was significantly more (maybe 50%) than on an equal surface area elsewhere on the conning tower hull. This caused the pressure hull steel in area of the trunk to finally ‘yield’ i.e.; fold-up and either tear or a weld fractured and allowed water pressure to equalize. All of the compartments aft of Aft Battery show this ‘crumpled’ effect of steel yield point being exceeded.

    An underwater explosion causes a similar Hydrostatic Pressure wave to propagate from the center of detonation expanding outwards equally. In this case I believe the torpedo detonated directly at the forward torpedo pressure hull near the port bow plane. This effectively made the detonation 5/8 inches (wall thickness of pressure hull steel plate) from actually being inside the FWT. This is a massively unequal force, and effectively the pressure wave penetrated and traveled into the forward torpedo room and aft. So the ‘Hydrostatic Damage’ to the torpedo room was effecting the Pressure Hull from inside (as well as all around the external pressure hull on Port Bow side).

    Following is pasted from previous Email.

    I think the #6 Torpedo detonated in the area of the port bow plane (possibly, as Bob suggested, a magnetic exploder event). Pressure hydrostatic (or hydraulic) pressure wave penetrated FTR from Port Side. This may allow for the ‘folded-in’ effect visible on port side. When this pressure wave continued to expand (inside FTR) it encountered the fully flooded MBT #1 (forward bulk heads exposed in photos). This Ballast Tank was full of water and it would be slightly more resistant to the hydraulic/hydrostatic effect. This tank and its ‘reinforcement’ more or less deflected or ‘channeled’ a larger portion of the blast wave aft and up.

    The FTR Hatch and Escape Trunk (having the largest external surface area by far of any of the hatches) was especially reinforced with several external welded strengthening rings (larger and more robust than standard). (I think I can see four of these in the photos and one is clearly visible at the ‘break-off’ point starboard side). And they are the reason the Escape Hatch is still standing as it appears to me that the top of the pressure hull (above what would be the internal working deck) is missing from that point all the way back to just forward of Control Room Bulkhead.

    (Note: I believe that the FWT Escape Trunk is slightly rotated counter-clock wise. The Escape Trunk Side Door is pointing off centerline and slightly toward the starboard stern. I believe this is a blast effect on these larger strengthening rings, driving the port side slightly astern regarding the starboard side)

    The pressure wave traveled aft and went out of or back out through the pressure hull at the Fwd Torpedo Loading Hatch (a natural focal point) and (inside the pressure hull) hit the Forward Battery Bulkhead. I think the top one-half of this bulkhead failed or at least was penetrated at this time. (The bottom half of Forward Battery, from main walking deck down is largely filled with battery cells. These are filled with fluid (dense), very heavy and protected underside by the full Fuel Oil Tanks). Again the bottom portions of both of these compartments are comparatively hardened (?) and stiffened. (Natural blast deflectors in this particular situation).

    The top of the pressure hull appears to be disintegrated from the ‘break point’ back to the sail or conning tower (near Control Room bulkhead). The expanding pressure wave internal to the pressure hull and expanding pressure wave external to the pressure hull cleared the superstructure and all ballast tank vent valves and piping, all the way back to the sail. It may have destroyed the sail fairing at this time. I noted from photo reviews the internal fabrications as debris and sections of ventilation ducting laying in the mid-line of Forward Battery compartment. These items started inside the compartment, and it appears that the top line of pressure hull is simply gone cleared down to the tank tops. I can find no traces of the Fwd Torpedo Loading Hatch or Trunk.

    When this weapon detonated at the port bow it had the power to displace the vessel to starboard during the break up / break off of the heavy equipment forward of impact. (Torpedo Tubes, Anchor and Chain, Fwd Capstan and Motor, Bow Planes and Hydraulic Motors, Bow Buoyancy Tank) It is likely that the dished-in or ‘pinched’ effect noted on starboard side (left side in photos) is showing the metal structures tearing off (at-from the Escape Trunk reinforcement ring) and carrying away too port side and down.

    I think Grunion lost Fwd Torpedo Room and Fwd Battery at this time. I believe I detect a ‘bulge’ or balloon distortion in what I think is remaining pressure hull at the Control Room Bulkhead. I think it is entirely likely that this bulkhead was breeched at this time also.

    If one or more of the water tight bulkhead doors were open, combined with the ventilation flappers and other bulkhead weaknesses a case can be made that the explosive effect carried through to the After Battery and contributed to AFB hatch being blown open. Certainly the photos show the very robust CRES trunk liner to be ‘bunched’ and crumpled up at the top of the ladder.

    October 18, 2007 | 10:35 pm


    I believe that your description of events is perfectly possible – actually most probable. Since Bob posted his observation about a collapsed pressure bulkhead I have also been considering that it might have been caused by the explosion effects within the hull.

    But it makes me wonder about another thing that has come up last week: the second pair of torpedoes floating off Kanu´s stern. I´t been suggested that they might have gotten loose from the FTR´s remains, their warheads separated by the force of the explosion. But if the pressure wave had enough force to push down a bulkhead… what would it have done to the thin skin of a torpedo (and its guts)? I don´t think any would have survived in a floating condition.

    October 19, 2007 | 5:05 pm

    The outer hull from immediately aft of the forward escape trunk to the break of the fairwater/conning tower is curled downward and inward all the way to GRUNIONs boot-topping, and until it was almost touching. The pics clearly show this…it’s one of Bruce’s “facts”. So the question is “How’d it get like that?”.

    (a) A magnetic exploder event over the main deck…which could nicely explain almost everything you can visualize on the wreck EXCEPT the inconveniently missing FTR. And I can’t come up with a workable theory that would account for it getting popped off like a zit. I guess it could happen…it’s just waaaaay down the order of probabilities IMO.

    (b) FBR imploded. As the FBR was compressed inward along it’s upper centerline by hydrostatic pressure, the outer hull was pulled/compressed inward into the void being created. If the integrity of the FBR was compromised (by exploding outward along its top), there would be no void to fill, the outer hull wouldn’t have displaced inward. It’d look like every other sunken sub that didn’t suffer catastrophic implosion, and have a reasonably intact outer hull (at least in this area).

    What I find interesting is that the outer hull is ONLY compressed down to her boot top in this area. This would mean that the pressure hull/FBR top only compressed downward a couple of feet (or less) as a result of the imploding process. Don’t forget, the actual pressure hull top was only a couple feet above the boot-top/waterline. To me, this indicates the FBR failed relatively quickly, which (to me) also indicates that the forward bulkead was likely damaged. Which would set up the entire sequence of events that ended with the ABR hatch being blown open.

    I’ve been working with the wreck photos, while I’m an analyst and not a tech, I’ve been able to enhance them somewhat. I’m reasonably confident I’ve been able to ID most the major wreckage lying in the FBR area. I see the radio mast w/antenna wires; deck supports; vertical deck supports; broken outer hull frames; what I think is a insulated radio antenna; deck cleat; PSP planking from either the main deck or the sub-deck crawl-ways; heavy spring-loaded flapper valve and the remains of its mesh cage; piping w/gate valve I think is part of the “10lbs Blow” system; and what I think (I can’t find a pic of one anywhere) is the mount for the JP Hydrophone head. All of which came from on or under the main deck. I think I can see the forward torpedo loading hatch, exactly where it should be, if the FBR was imploded and the forward bulkhead collapsed outward, and the remains of the FTR top was displaced downward as the FBR imploded. You can see what could be the “ghost” of the distinctive rounded lip buried under the rubble, directly aft of the FTR escape trunk, centerline, and at roughly 45 degrees downward.

    What I don’t see (lying in the FBR), is anything that came from inside the pressure hull.

    The Forward escape trunk is oriented correctly. I’m looking at a pic of the CODs…it points sternward at about a 5’oclock position (165-170 degrees).

    Regardless, I’m certain that the events in/around the FTR did serious damage to the forward main deck/sub-deck structures.

    The periscopes; they speak to me, I’m just not sure what they’re saying. If the accounts are taken at face value, they’d indicate that a periscope was raised. What we see is the search periscope raised slightly, and the attack scope is either lowered or gone.

    (1) Why would they have been using the search periscope while being actively shot at? If they were, then the bending of the shears must have occured before it was lowered completely. Could the implosion of the conning tower have raised it slightly? If so, then again, this had to have occured before the shears bent.

    (2) What is the status of the attack scope? Gone, or lowered?

    A couple of web sites showing the wrecks of PERCH and LAGARTO. Interesting pictures, and you can see some of the hardware, structural members, and deck supports belonging under the forward main deck in the pics.

    USS Lagarto

    USS Perch

    October 20, 2007 | 6:31 am

    Periscopes; The attack periscope is broken off and lying across the fairwater, port side, on top the bridge cowling. That’s not the RDF mast as I originally thought, dimensions are wrong…but bang on for the fully extended attack scope.

    October 21, 2007 | 2:36 am

    Bob, all,

    I can´t see things as clear as you on the pics but if the attack periscope is broken off, could this have happend on impact against the bottom? I mean if Grunion hit bow first could the force of impact have broken off the attack scope? Would that have bent the shears forward? Is the search periscope raised beyond the conical end, which would not have been jammed by the bent shears?

    October 21, 2007 | 3:45 pm


    I don’t see clearly, these pics blow pond water. Going cross eyed trying to enhance them.

    Periscopes; I’d think it would have went forward if it was impact against the bottom. Could they have flexed forward on impact, then whipped backwards, finally breaking off and falling backwards when the stern hit? Could also be a fishing net knocked it off post event even…do they fish that deep?

    There’s 3 choices for how the sheers bent; (1) Impact against the bottom, (2) Wreckage hit them, (3) The explosion from whatever cause. I’ll throw in a #4; All of the above, or best 2 out of 3.

    The search scope is only sticking out a little way. The easy explanation for the search scope would be that the sheers weren’t deformed until GRUNION hit bottom. But on the way down, compression/implosion had pushed the scope upwards a few feet in the well. Another theory would be that when the sheers bent, it pushed the search scope up a little.

    Here’s some questions;

    (1) Would GRUNION still have her torpedo loading crane on her foredeck? I think WAHOO still has hers on her deck?

    (2) Can anyone point me to a picture(s) clearly showing the (stowed) loading crane and base, and the base of the radio antenna mast on an early GATO?

    (3) In picture “2nd sighting port side 42” (41 & 43 as well), what is the “thing” almost centered in the pic? I don’t think it’s a stanchion. It looks like it’s got a stainless steel base, two clamps around it, and appears to have a rubberized coating on it. I can’t tell if those insulated cables are leading to it. Antenna? Stanchion? Guy wire base for the radio mast? The light pole from the very bow?

    (4) While you’re looking at that pic, what’s the little “roller” looking gizmo to its right that looks like its got 2 horns sticking out the top?

    (5) In pic “2nd sighting port side 40”, to the extreme left, under the remains of the escape trunk sub-decking, 10 o’clock from the flapper valve, what’s that item of equipment lying on top the debris? Could that be the JP Hydrophone mount (I’ve never seen one)? If not, any ideas?

    October 21, 2007 | 10:37 pm


    I´m not sure this is what you need of a JP hydrophone, but try this link. There´s also a picture of the training mechanism (inside the pressure hull), and it seems that what´s between these two would be just a steel rod.

    Ed Walson
    October 22, 2007 | 2:07 am

    Bob, Most of the time the torpedo’s were loaded using a tender or yard crane. However the crane (stiff leg) could easily have been rigged. If not it was stored (in component pieces)under the superstructure probably in the area of escape hatch ladder (for easy access). It was a bitch to rig up. It would have been stowed very tightly with well fitted brackets so it would not come loose and rattle around.

    I haven’t seen a JP Hydrophone mount either.

    Your (3) photo #42 is very near what I think is the FBT #1 vent pipe to vent valve (from tank top). The spring is part of duel vent valve actuator, the grating was cage to prevent debris from interfering with operation. The fuel tank vent valves were locked shut but they were equiped for operation similar to MBT’s. The shiny one is I think a ‘use fuel’ pipe it appears also in photo #43 entering lower left. I don’t think it is insulated, I think it is collapsed. I think the pipe material in tungum not stainless. I have seen that connection in other photos as seagrowth doesn’t stick. Same with the articulated reach rods for the Ships Salvage Air valves and Air Connections.

    Look my email up from above and send me yours. Frankly when reviewing these photos I am all over the ball park, and my attempts to “inhance’ things are failures. Maybe we can get on the same page and review these in batches?

    When I first saw the periscope in semi-retracted position I believed that the extreme pressure which conning tower was subjected too over came the hydraulic system (rams) of the scope and pressed it firstly back into the periscope housing which lives in the pump room. I got this from a conversation with a very good engineering officer along time ago. The periscope hull penetrations are a large natural weak point in the conn pressure hull. (periscopes have high surface areas external to hull, especially when they are fully extended) Just from memory the engineering office thought that in worst case it could drive the scope clear into negative tank. That conversation is probably the only one I remember…

    Ed Walson
    October 22, 2007 | 3:46 pm

    Bob, Go to last on list of line drawing is photo of model of Gato class with your ‘shape’ from photo #40 above on deck forward radio antennas.

    October 24, 2007 | 10:00 am

    Guido…Thanks! I suspect that there had to be a brace/mount for the hydrophone head located outside the pressure hull, otherwise with that long of an unsupported shaft it’d walk in the packing gland, and bend the first time someone looked at it cross-eyed.

    Ed…I’ll drop you an email.

    Charles A. Thompson
    November 12, 2007 | 4:56 pm


    Being a submarine enthusiast for the last 50+ years, I have followed the Abele brothers quest since it was first made public. Having lost my own father in WWII, my admiration for their effort is boundless.

    That said, I must say that I disagree with the scenario so far advanced for her loss. I have reviewed all the photographs in detail, have read the eye witness accounts presented, have been involved with the fabrication of pressure vessels for 30 years, and studied the few available photo’s and accounts of other deep water submarine losses, and I find nothing that suggests that Grunion’s loss was a result of a circular run of one of her torpedo’s. So, with full appreciation for, and no criticism of the expertise and effort so far set fourth, let me propose a possible sequence of events that fully fits both the eyewitness accounts and the present condition of the vessel.

    To support my theory, let me set forth those events which are known and which would influence Grunion’s loss. Commencing approximately 0545, 31 July 1942, Grunion made three submerged attacks on the Kano Maru. As a result of the first attack, the Kano Maru was damaged and stopped by one of two torpedos fired. In the two subsequent attacks, a minimum of four torpedo’s were fired, three of which should have exploded. During the attacks, the exposed periscope was fired on by the Kano Maru, with small arms and an 8mm (3”) deck gun. After the third attack, the submarine apparently broached and was fired on, with one round impacting in the wave of the exposed portion of the submarine. There are three known written accounts of the attack, one by Aiura, an experience military man, one by Dr. Rikimaru Nakagawa, nautical experience unknown, and one by Kenji Hamada, a “contract newspaper man”. Subsequent to the attacks, wreckage and apparently oil rose to the surface, and at least one dud torpedo body was towed into port.

    In my opinion, an examination of the wreckage photographs reveals that all watertight compartments, with the exception of the control room, have imploded, with the bow pinched off by external pressure immediately forward of the forward escape trunk. What follows is a scenario which allows for those conditions.

    Grunion has made three attacks and Capt. Abele has watched torpedo’s bounce off his target’s side and pass harmlessly under the target. For reason or reasons unknown, after the third attack, Grunion broached. According to THE FLEET SUBMARINE, NAVPERS 16160, June 1946, (NP 16160) in normal submerged operation, the vents should have been closed, the safety and bow buoyancy tanks flooded, and negative tanks empty (see chapter 18). With the boat broaching close to an armed enemy, Cdr. Abele would have been encouraging his diving officer to get her down (An officer with Cdr. Abele’s experience would not have surfaced that close to an armed enemy.) The diving officer would have ordered hard dive on the fwd diving plains, and probably the stern plains, flooded negative tanks, and ordered engines ahead full. He could have cycled the vents to get rid of any air the ballast tanks. He may then have shifted the stern planes to hard rise(their present setting) to get a down angle on the boat, (NP 16160.). He may have shifted water from stern to bow trim tanks. I would love to get an experienced Gato class diving officers opinion on what he would have done.

    Mr. Aiura’s account then says “Just then an 8cm gun shot hit the washing wave, made water column and dull water explosion sound.” The Grunion, at that time would have been trying to get heavy, not light. When the 8 mm round hit “the washing wave” beside the conning tower, it could have passed through the thin superstructure below the conning tower, and impacted on the control room. An impact in the forward end of the control room would have caused immediate flooding, and wounded/killed the tracking party, the diving officer, bow and stern planesmen, possible the COB on the vents and the Petty Officer on the air manifold. This would make recovery from the dive difficult.

    With the control room flooding, engines going ahead full, the boat heavy and getting heavier, and a down angle, Grunion would have taken an increasingly larger down angle which could have exceeded 45o (see WAR FISH, chapt “Frustration”(Grider)(52 o+) and Luck of the Draw, Prologue & “Out of Control” (Ruiz, a good account from the diving officers prospective) for the Pollack incident, and WAR IN THE BOATS, chapt “Disaster” (Ruhe )(42o) and SUBMARINE REPORT, DEPTH CHARGE, BOMB, MINE, TORPEDO AND GUNFIRE DAMAGE INCLUDING LOSSES IN ACTION, 7 DECEMBER 1941 TO 15 AUGUST 1945, War Damage Report No. 53, (BUSHIPS), 1 January 1949, para. 17-17 (BD). for Crevalle incident). If control room personnel were functional, ballast, safety and bow buoyancy tanks would have been blown, and the planes set to hard rise. At some point, as the angle increased, the hatch between the conning tower and the control room would have been shut. Cdr. Abele probably ordered both engines back emergency (NP16160, chapt 18). But it would have been too late.

    At some point after 600 feet, with the bow possibly 150 feet or more deeper than the stern, the bow plating in the FTR would have begun to distort. Shortly thereafter, the forward part of the FTR imploded and separated. The implosion is not a small or low order event. The physics involved defy imagination. There is tremendous heat generated by the bending metal and the adiabatic air compression (maybe 1000oF+). This would be immediately cooled by the 29+ degree F seawater. The force of the water hammer hitting the FTR/FBR bulkhead is incalculable (example: the total static load on a 10 foot diameter circular bulkhead at 600 feet is approximately 3,000,000 pounds. That is static, not dynamic load.). As a result of the hull distortion and pressure, the FBR would have imploded almost simultaneously (see BD, chapter XVI). The implosion of the FBR sucked the part of the superstructure (pilot house) forward of the forward periscope sheer support into what was once the Chief Petty Officers quarters and Yeoman shack. The top of the pilot house is visible in photo Attack Analysis 3, photo, 4, as a flat, downward sloping surface with a semi-circular leading edge, protruding forward from the base of the forward conning tower bulkhead in the center of the photo. A porthole in the pilot house is visible just to the left of the crab.

    With the entire forward section flooded, shortly thereafter, the remaining unflooded compartments aft imploded with such force that the ABR hatch was blown open, and the 3” deck gun, mounted on top of the ABR/FER bulkhead was thrown backward (toward the bow) with such force that it is now at full elevation. The conning tower and surrounding superstructure, sitting on an already flooded control room, is relatively undamaged. As for the point of impact for the 8mm round from the Kano Maru, in the photo below (I’ve lost your original designation) just to the right (aft) of the lowest large white sponge, there is a circular shadow which could be the point of. An 8mm shell does not make a large hole if it does not explode on contact impact (see photo’s of the hole made in the Japanese 2 man submarine which tried to enter Pearl Harbor, and was sunk by gunfire from the USS Ward.). A better view is required. On the surface these events could have looked like “bubbles running on the surface figuring half circle” and “Then just at the head-end of bubble running, big black-brown water arose,…”.

    As mentioned in a previous submission, a more accurate translation of the available Japanese reports would be of immense value. For an appreciation of the difficulties involved with translation of WWII Japanese reports, see FIND’EM, CHASE’EM, SINK’EM, (Ostlund) for the trouble he had tracking down the fate of the USS Gudgeon (SS-211) The sources in Japan he used for an accurate translation are also identified. Also, SUBMARINE REPORT, DEPTH CHARGE, BOMB, MINE, TORPEDO AND GUNFIRE DAMAGE INCLUDING LOSSES IN ACTION, 7 DECEMBER 1941 TO 15 AUGUST 1945, War Damage Report No. 53, (BUSHIPS), 1 January 1949 is of significant value for understanding what happens to a damaged WWII submarine. It includes a number of chapters on specific submarine damage, chapters on Japanese ASW techniques and weapons, Behavior of Underwater Explosives, Hull Damage and Strength, Stability, Buoyancy and Flooding, and much more. If the Abele family would like a copy, let me know, I have had it put on a CD.

    Regardless of the actual cause of Grunion’s loss, the real culprit is the Navy Bureau of Ordnance. Had any one of the 3 torpedoes which should have exploded done it’s job, Grunion would have returned to Pearl Harbor with a broom lashed to here periscope, and probably a Navy Cross for Cdr Abele. At that time in the war, aggressive skippers like Cdr. Abele are exactly what the submarine force needed and did not have.

    Charles A. Thompson
    November 12, 2007 | 5:07 pm

    In the ninth paragraph, ninth line, add “impact” to the end of the sentance. The photo which most clearly shows the possible point of impact was deleted when I posted.



    November 18, 2007 | 2:08 pm

    Charles Thompson could you contact me at Your post is very interesting.

    I have been heavily involved in preparing a set of DVDs from the original ROV video organized by parts of the sub. The plan is to send a copy of these DVDs to those individuals who would be willing to help out in this analysis. There are several hours of video and there are 60 frames per second so there is a lot if information that may be useful. It is not always clear. Hopefully I have it organized and classified so at least you know the general area you are viewing.

    November 18, 2007 | 7:11 pm

    The accounts are pretty emphatic that the KANO MARU was armed with the old pre-WW1 British pattern 8cm guns. Known in IJN service under various designations, using various mounts, but they’re all basically license built variations of the Armstrong AN. This weapon fired a HE Common round with a 0.71 lbs bursting charge and a Type 5th Year nose mounted, point detonating fuze.

    In this scenario, after impacting the “washing wave”, passing through 20-30′ of water, penetrating at least one (likely more) layers of the superstructure, and punching through the 9/16″ thick pressure hull and ultimately detonating within (and wiping out) the Control Room, it; (a) Threw up a “water column” from within the confines of the Control Room and through a 3″ hole, (b) made a “dull water explosion sound”, and (c) stained the water with the characteristic results of a large sub-surface explosion. All noticeable enough to comment on from a distance of 400+ meters. This is all rather a lot to ask of a pretty unimpressive round with a point fuze and a 0.71 lbs picric acid bursting charge.

    NOTE: The specialized IJN ASW “Diving” round didn’t come out till mid-late 1943. The performance (which can be assumed to be superior to “standard” rounds used in this role) was penetrating approx. 0.5 inches of steel at a depth of 8 meters/24 feet. Had a minimum range of 700 meters due to richochets, a 1.5 lbs bursting charge, and required a specialized (and complicated) fuze to work. If it did work.

    NOTE: USS WARD vs. IJN Midget; WARD engaged the midget at pointblank range, and used a 4″ gun (1.4 lbs bursting charge). The midget was fully broached (none of this “seemed like it was going to surface”, “ripples”, or “hit the washing wave” business) on the surface. The round impacted/penetrated the port side of the conning tower (probably 1/4″ steel or so) leaving a nice 4″ hole, detonated more or less instantaneously (okay, call it a 0.001 second delay or thereabouts)…with a few small shrapnel exit holes on the starboard conning tower side, and no obvious deformation of the subs structure.

    NOTE: IJN submarines didn’t generally have large, tall, fully plated periscope shears like early model GATO class subs. You saw the scopes, then you saw the top of the Bridge/Conning Tower. This is something a retread officer like Cpt. Aiura would be unlikely to be familiar with. I strongly suspect that what was reported by Cpt. Auira was, at most, the tops of the shears just breaking the surface. You actually do get a ripple or “washing wave” from periscope shears under such circumstances. He talks of the “sub seemed to begin to surface”, a “ripple on the surface”, and “began washing the conning tower”…but no actual mention or description of seeing a submarine/conning tower.

    The round was reported as striking “the washing wave”…not the conning tower or the GRUNION, which would be the case if it was actually exposed. Of note here is Nakagawa’s report; he describes the bubble, the results of a large sub-surface explosion…but no submarine. He exclaims “Must be submarine!”…which would be an extremely odd thing to say if there was a surfaced/broached submarine or conning tower sticking up out of the water. Again, no mention of seeing a sub until he mentions the “thin black bar”. I imagine Aiura was using binoculars, and Nakagawa was using his Mk.1 eyeballs BTW.

    David Dodge
    November 19, 2007 | 7:46 am

    I have read and followed this thread from the start and want to applaud Charles Thompson for his very fine post. I also would like to add a thought that I think adds to his theory.
    If indeed a torpedo hit the submarine, I find it hard to believe that the eyewitnesses would have failed to comment on the enormous explosive effect of the 8cm projectile. A profectile that holds maybe 25 lbs. of powder vs. a torpedo that has 500+? lbs of explosives.

    Bill Bolton
    November 23, 2007 | 10:47 am

    I too, have been following the search and now the discussion regarding the open hatch. I am a Systems Engineer and I’m looking at things from a whole systems perspective.

    Items of interest to me:
    A open hatch
    How could an older design 8cm round have such an impact that it sunk the Grunion?

    The evidence of the hatch seal and sheared dog indicate that a severe overpressure event in the compartment(s) below, blew open the hatch. The overpressure event would have had to occur with the sub not too far below the surface in order to overcome the hydrostatic pressure from the sea.

    That leads to the question of how did the overpressure event occur? Indeed as Bob mentions, the 8cm round fired from the KANO MARU would have had to pass through a wave, decking, the pressure hull and then explode. I agree, this is possible but unlikely.

    But consider the possibility that the Japanese round was a dud or damaged by contact with the water. It could pass through the wave, decking and pressure hull. Furthermore, what if the the ‘dud’ round entered just aft of the CT, struck an American 5″ round that was NOT a dud, positioned in readiness right below the After Battery Room Hatch? The result would be a much larger detonation blowing open the hatch and dooming the boat. Also a possibility is that the detonation could have fractured the pressure hull and caused the forward collapse of the CT.

    Imagine the following scenario:
    Captain Abele is thinking ahead after numerous torpedo failures. The KANO MARU is dead in the water, easy pickings if he acts quickly. Sonar has reported that engine noises have ceased. He issues orders for 5″ gun surface action intending to further damage or sink the KANO MARU.

    He imagines that the freighter is lightly armed. Crewmen break out the 5″ shells and stand ready to open the gun access hatches and begin firing when the 8cm gun on the KANO MARU opens up. Perhaps he is too close or he is surprised by the 8cm gun. In any event, Captain Abele belays the deck action order and calls for a dive.

    Stern planes are positioned down when the CT broaches and the fateful 8cm shell enters the pressure hull striking and detonating one (or more) of the 5″ shells. The detonation overpressure shears the After Battery Room hatch dog and seeks the easiest way out. One of the easy ways out for the pressure, is past the hatch seal. The seal flutters and dislodges itself from the seal groove. The seal first blown outward by the blast and secondly blown inward by the onrushing ocean, wraps itself around the hatch.

    The spout of debris, water and air from the ABR hatch is observed by the KANO MARU. The hatch which is now blown open, admits the sea flooding the control room and the remainder of the scenario painted by Charles A. Thompson occurs.

    David Dodge
    November 24, 2007 | 4:24 am

    Waaaaay up the page, on the 9th post of this thread, I suggested that the 8cm round could have possibly punctured a high pressure tank, manifold, or line. These items seem to be in abundance at the location of the washing wave and perhaps they could produce the overpressure?

    I admit there is a bulkhead/door between the control room and the ABR that should have been secured, but, in a rush to get ready for battle surface, perhaps there were men rushing between compartments and the door was open at the time.

    On another note, I notice that many people want to dismiss eyewitness accounts to further a theory. As with the Pearl Harbor sinking of the midget submarine by the USS Ward, the impact point was finally proven to be exactly where the crew said it was. It seems to me, that of all the variables that we cannot know, we should at least give the eyewitnesses some credit. If they say it hit the washing wave, then lets work the problem from there. If they all fail to notice the explosive effect of a torpedo vs. a whimpy 8cm projectile, then perhaps there wasn’t a torpedo…

    Bill Bolton
    November 27, 2007 | 4:04 am


    I was not trying to minimize your earlier post but rather add a plausible scenario that would explain the damage to the ABR hatch from an 8cm shell landing near/in the ABR .

    If we add the eyewitnesses account of the shell landing near the forward part of the CT, then the idea of an 8cm shell making it’s way through the hull and striking a 5″ shell is still plausible as the gun access trunk is at the very forward part of the CT and men would possibly be standing there ready for surface action. In fact, an explosion of a 5″ shell in the control room might explain the collapse of the CT.

    From the images of the gun access trunk (Conning Tower Hatch 13) , you can see that the hatch mating lip is deformed, the only question is how did it become deformed; after the CT collapsed or by a detonation from below.

    Regarding the overpressure from a broken/severed HP line it would depend (if I remember my physics) on the volume of the space that the HP was released into and the volume of the stored HP). Gut feel (always a bad thing) tells me that had a HP line been severed, it could have disabled the crew, but is it enough to shear a dog off of the ABR hatch and blow it open to the sea? I don’t know.

    Bill Bolton
    November 27, 2007 | 4:15 am

    I just went back a looked closely at images of the Gun Access Trunk Hatch and if you look at the image; Conning Tower Hatch 7, it appears the the left hand (or upper) strut is bent upwards (and outwards) while the right hand strut appears to be somewhat straight. I don’t know the normal shape of these struts but a photo of one in normal circumstances might be instructive.

    Travis Mullan
    November 27, 2007 | 9:20 pm

    Firstly, I would like to thank the men of the Grunion and all of the others ‘on eternal patrol’ who made the supreme sacrifice so that we can live our lives in freedom. My interests have been in marine salvage and I provide non-professional research assistance to artists, maritime museums and model builders in this area. I am in the process of writing a book on marine salvage and hope to have something published in the next few years. I have also been interested in the diesel boats since my early childhood and have found the recent discoveries of the Wahoo, Legarto and now the Grunion quite exciting. So many submarine related books have stated over the years that what happened to these boats would remain a mystery forever and now they are being found and giving up their secrets.

    In looking at the on line pictures of the sub it is obvious that she suffered a catastrophic detonation at her bow as stated by other writers. This could have been due to a circular run or may have been from a cause yet to be discussed. If, indeed, the boat was surfacing for gun action or a broach the bow may have appeared prior to the conning tower becoming visible and this could have been where the Jap shell struck the sub in ‘the wash wave’. If this were the case it is possible that the shockwave from the shell caused a sympathetic detonation of a war shot still in one of the tubes. Whatever the case may be a significant amount of the bow was lost completely. In the case of any pressure vessel, such as the pressure hull of a sub, the weakest points will be the openings (battery room hatch, escape hatch and torpedo tubes). The torpedo tubes, being clustered in the end of the pressure hull and in a tight group of six, would be the weakest point of all which may explain the massive damage in the tube area.

    In cases where a compartment of a ship, be it a surface ship or a sub, is breached the buoyancy provided by that compartment is lost. As the water enters the area it will add its weight to that area compounding the problem. The loss of the buoyancy provided by the forward ballast tanks and bow buoyancy tank (if empty) added to the problem as well. In this case it would appear that the Grunion took a bow down attitude and began to sink immediately following the detonation. A bow first contact with the bottom may explain the damage to the remainder of the bow area forward of the escape trunk. I am not familiar with the under water terrain in this area so I can not venture a guess whether she tumbled down a steep slope or impacted directly with a flat bottom. A chart of the wreck area would be useful here, as would any photos or video of the bottom in the area.

    It appears that the blast was limited to the torpedo room as the forward battery area seems to have collapsed as the sub passed crush depth. Also, the forward escape hatch is not compromised which would support this theory. The escape trunk lower hatch may have contributed to this if it were closed which would be normal in a combat situation. The fact that the forward battery is crushed proves that the torpedo room/battery room bulkhead is intact. The battery room is crushed from above which is, most likely, due to the strength of the deck over the battery itself preventing a bottom up deformation of the hull. This deformation of the overhead is also quite evident in the after torpedo room.

    Moving aft, the conning tower seems to have been deformed through pressure exerted downwards through the periscope sheers which have probably become deformed by contact, possibly with the bottom. The top of the conning tower pressure hull is collapsed downward on the port side and the after bulkhead has been pulled up and forward. The forward hatch does not seem to have been forced up by a blast transferred through the hull as stated in earlier messages. On the contrary, it appears to have been forced down on its opening side by the deflection of the upper conning tower pressure hull (my opinion). This is shown in analysis 1. Also, the deck supporting elements from the upper conning tower sides (sheet metal) are bent down where they were attached to the support structure for the periscope sheers (see conning tower hatch photo 6 magnified). To support the contact theory of the periscope sheers with the bottom, maybe, note the difference in the deflection angle of the upper assembly with that of the lower. If the periscopes were pulled forward by an implosion of the conning tower pressure hull the deflection would be uniform.

    By the way, the binocular looking device mounted on the forward end of the cigarette deck is a gun director which should be duplicated on the ‘bridge desk’ at the forward end of the sail without a support stanchion. On some boats these were referred to as Target Bearing Transmitters (TBT).

    Any other photos or video from the ROV would be helpful in determining what actually happened to the boat and I would appreciate the opportunity to view what you have available. I hope that this is of some help to you.

    Travis Mullan
    November 27, 2007 | 9:25 pm

    Check out for a great virtual tour of a WWI sub.

    David Dodge
    November 27, 2007 | 11:52 pm


    Please understand that my post was not a reaction to anything bad. I was actually happy to see someone address the ABR hatch and get off of the torpedo bandwagon. I was really trying to reinforce Charley’s sensible post and was very happy to see you bring up the open hatch, which, is regularly ignored when people push the torpedo hypothesis.

    My example of the location of the impact was mainly in reference to the disrespect the crew of the USS Ward got…and not a response to your “aft of CT” suggestion, though, I can see now how it looks that way. Please accept my apology. Many posts have discounted what the Kana Maru witnesses said by adding comments pertaining to their qualifications, which, I think, is not fair. As merchant-sailors, they could possibly be very well-qualified due to the fact that they could have been doing this since they were children. Some, could have been veterans, with many years under their belts. We do not know who these merchant-sailors were, but, by hitting a submerged sub with an ANTIQUATED PRE- WORLD WAR ONE GUN, I think that qualifies.

    I appreciate you thinking about the high pressure line. Yes, perhaps that is not enough pressure to shear a dog, but, if the hatch was loosened almost all the way in preparation for battle surface..? (in wartime, shortcuts are probably taken and I can see them doing just that, sea-pressure would keep the hatch closed until the boat is pretty much on the surface and then the hatch would pop open by the spring at the earliest time possible – thus speeding up battle readiness)

    Travis Mullan
    November 28, 2007 | 12:31 pm

    Pardon my typo on the previous posting. It should read WWII sub.

    Bill Bolton
    December 7, 2007 | 1:57 am

    I just did a bit of algebra/physics (very rusty) on the amount of force required to open the ABR hatch while under water. Of course, I’m disregarding the mass of the hatch and the assist spring and the force required to shear the hatch dog.

    At 5ft under the surface, a 3′ diameter hatch would have to lift over 5616lbs or 2.8 tons of water just to get the hatch to crack open

    At 10ft under the surface, the force is 11,232lbs or 5.62 tons.

    At 15ft, the force increases by over 50% to 16,848lbs or 8.04 tons.

    When you combine this wtih the force required to shear the hatch dog(s), it indicates that a very significant impuse occured, enough to force open the hatch to the sea. Although, the shearing force makes the lifting force seem puny by comparison, it would seem likely that the hatch depth was relatively shallow when the impulse occured.

    Any Materials Science guys out there? How much force would be required to shear a box shaped (in cross-section) bronze hatch dog?

    Would a single 8cm round have enough power to do this? I don’t know, but perhaps some of you have the knowledge to calculate the impulse pressure from a 8cm round into a closed container.

    My feeling is that somehow the 8cm round set off a 5″ round. Remember, a 5″ round is at least 50% larger than the 8cm round and we cannot rule out multiple rounds being detonated and this is what blew open the hatch.

    Mike Green
    December 11, 2007 | 10:04 am

    I have only read the posts so far, however, an argument against the circular run theory is that the eye witness accounts do not refer to the massive water column that would have been present.

    I am also pretty sure that the gun ammo would have been stored in a ready service locker forward and below the bridge (need to check the books) and if correct the 8cm (3″) round could have set off an explosion there. Not as big a water column and could have punched a hole in the conning tower forward. The net result would have killed or disabled all those in the conning tower (CO, XO, QM, Helmsman, TDC operator. etc) and resulted in a torrent of water down the hatch into the wet side of the control room (right on top of the trim manifold operator if I remeber correctly) with a subsequent loss of depth control. Anyone who has ever struggled against the flooding problems in the submarine damage control trainer can tell you about how hard it would be to shut the hatch to the conning tower.

    A big unknown that plays a role is the juice in the can. Where was the ship in the battery charge cycle? Speed can carry weight but with a ship already heavy and trimmed with a down angle it might not have taken much whatever the cause if the battery were down.

    No promises but I will try to interest some of my friends (all submariners and engineers and retired)

    I’m off to look at the pictures to see fo myself.

    Mike Green
    December 11, 2007 | 11:01 am

    Ooooops! Check the photos first. The Grunions gun was aft of the conning tower so it is likely that there was no 5″ ready service locker forward (though many of the boats had their gun forward). The boats with their gun forward had a ready service locker on the forward part of the conning tower. After the guns were taken off it was used as waterproof storage at sea.

    Zack Galler
    December 12, 2007 | 7:35 pm

    There appear to be a number of analysts on this site who are open to the fact that the circular run hypothesis may be credible.

    I would suggest that to establish that credibility several inconsistencies first need to be thoroughly addressed.

    Those inconsistencies are:

    State of the bow:

    1. None of the steel surfaces which are normal and close to the hypothetical explosion of a torpedo’s 643 pounds of Torpex show any penetration damage, indications of shrapnel impact, nor any of the concavity that is characteristic of an explosion of that magnitude.

    2. The break in the hull appears significantly bent inward (i.e. “crimped”). This implies a strong radial, inward, and consistent force acting on the top and two sides of the hull. The best candidate for a large, even inward radial force is hydrostatic pressure. Not a torpedo. Warheads create extreme localized overpressure.

    3. It is difficult to form a hypothesis that is consistent with both large-scale hydrostatic damage and damage from a near-surface torpedo explosion in the same compartment.

    Aiura’s ability to describe the location of the sub precisely gives his description of the confrontation great credibility. His words should not be taken lightly. In that sense:

    Aiura’s description of the #84 shot

    Aiura has just seen six torpedo firings with one explosion. On that morning, he is as well calibrated to report and document a torpedo wake and explosion any human on the planet.

    Yet, he doesn’t report seeing a seventh torpedo wake, (or a circling 6th torpedo) even though he’s watching the Grunion from the final appearance of the periscope at 06:10 onward. Of the top things on his mind, high on the list is looking for the next torpedo wake from Grunion. He described watching the submarine with clenched fists.

    After he fires and observes the impact of shell #84, he reports a “dull water explosion sound”.

    Contrast this to his description of the earlier torpedo explosion, which he describes as “large explosion and sound occurred that was like a rumbling of the hell ground”.

    If you go to you will see film of a submarine being hit by a Mark 14 torpedo. Although that video lacks audio, few would describe the event as generating a “dull water explosion sound”.

    Synchronicity between the 84th shot and impact of the torpedo

    The circular run hypothesis implies a synchronicity between two independent and rare events: shell impact and the detonation of a circular run torpedo.

    Though possible, the combination is extremely unlikely. It is like being struck by lightning twice in the same day.

    Aiura reported that shell #84, “made water column and dull water explosion sound. Also we saw the swell of heavy oil. All crews shout ‘BANZAI!’ That observation of synchronicity was not from one person but from the entire crew.

    Something happened coincident with the 84th shot. The evidence is overwhelming that it was not a torpedo hitting the Grunion.


    For those who believe in the circular run hypothesis, it would seem very important to first address these inconsistencies.

    December 14, 2007 | 1:58 am

    1-3. A non-impact explosion via magnetic exploder would most definitely create serious hydrostatic pressure. Damage appears to me to be more localized to the port side. Is it convincing or definitive? No. But it’s definitely more convincing than any of the round impact theories put forward as yet. The investigation is still young, and IMO isn’t going to be settled until a professional naval engineer evaluates the material. I’d be interested in what a professional has to say about a non-impacting shot crossing the GRUNION’s bow and exploding.

    “His words should not be taken lightly.”

    They’re also not gospel. HUMINT is pretty slippery stuff at the best of times, and we’re also dealing with an “interpretation of an interpretation”, from a guy who isn’t available to clarify his account. The modern Japanese language both spoken and written is virtually a different language from the WW2 era. I’ve seen at least 3 different “translations” of that account, all different to varying degrees. And the descriptions are so sparse we’re parsing each word for content (For example; Just what did “water column” mean to Auira?). What’s been changed, what’s been lost, what are we (or the interpreter) just not getting? Try “interpreting” a teenagers text messaging into English…think you’d lose meaning based on cultural or contextual bias? It’s also unclear if that account was taken from the original 1960’s magazine article or the period official report. Note the follow-on material seems like a synopsis from someone who skimmed the highlites of the material on file. So what nuggets of pertinent info got glossed over?

    “rumbling of the hell ground”

    Exactly. He just had a torpedo explode directly under his heinie, and transmitted to him via the ships structure. I’d forgive him for being less impressed by one 400+ meters away. Not to mention he’d just fired off 84 rounds of 3” naval gunfire, and had numerous rounds of 13mm heavy machine gun ammo fired off in his very close proximity…likely from the same bridge wing he was observing the GRUNION from. Anyone of the three would tend to dull your hearing somewhat. All three together?

    Let’s also not forget “self-interest”. Aiura was retired after a lifetime of service in the IJN apparently, then mobilized and given command of a conscript freighter. Service noteworthy by the fact it left no other mark than this account that I’ve found. His immediate predecessor in command of the KANO MARU went from being the Chief Navigator and DC Officer of battleships and a fleet carrier to command of a Yangtze River gunboat, assorted auxiliaries, and the KANO MARU. And ended up being sent to Truk to starve. I strongly suspect Aiura’s career followed a similar trajectory. Maybe this was his moment in the sun. Not very many Japanese merchant skippers could claim to have sunk a USN sub. (maybe 1 other?)

    In the same article, he mentions that they didn’t get credit for sinking GRUNION because he was a “reservist” and wasn’t trusted. One of the possibilities is that Aiura suppressed or selectively modified facts to support his contention that the KANO MARU sank the GRUNION. Possibly even unknowingly. Selective interpretation and/or reporting of the facts is something WW2 Japanese officers were particularly skilled at.

    Am I dissing Aiura? Nope. Stating facts that have to be taken into consideration when evaluating material such as this.

    “a “dull water explosion sound”

    I’ve been involved in detonating 10’s of thousands of tons of explosives, to include sub-surface. They do sound dull, depending on water depth and conditions. Read some accounts of the Atlantic convoys…torpedo explosions observed from accompanying ships are often described as a “dull thud”.

    “He described watching the submarine with clenched fists”

    Nakagawa DOES mention a bubble trail and other details that seems to have escaped Aiura’s eagle-eyed gaze and intent scrutiny.

    “bubble running on the surface figuring half circle just 2 or 3 hundreds meters apart from shipside”

    “just at the head-end of bubble running, big black-brown water arose”

    “after a while a black thin bar appeared on the surface then fell down and submerged”

    All “minor” details Aiura overlooked or neglected to mention BTW…unless Nakagawa was puffing smoke. I’d have to also go along with the submariner, and figure a known bubble emitter in the water is likely to be responsible for the bubble trail noted.

    “Synchronicity between the 84th shot and impact of the torpedo”

    “The circular run hypothesis implies a synchronicity between two independent and rare events: shell impact and the detonation of a circular run torpedo.”

    As opposed to the preceding 83 rounds he’d cranked off? Who’s to say they were perfectly in synch? Again, Auira? One of the truisms of war is that the winner writes the history books. For that matter, to be precise, the account states the round “hit the washing wave”…not the submarine. Auira implies the round hit the submarine, but never actually states it, and we the reader assume this is in fact true. Is it?

    Something totally lacking from the accounts is any description of the conning tower of the GRUNION. Nakagawa’s account is striking in that NO mention is made of the submarine other than he exclaims “MUST BE SUBMARINE” because of the bubble trail he saw. I’d have to say that would be a remarkably silly thing to say if he was looking at a conning tower poking up out of the water?

    “Though possible, the combination is extremely unlikely. It is like being struck by lightning twice in the same day”

    Funny you should say that. The phrase I was thinking to describe the possibility of a 8cm instantaneous fuzed HE Common round fired from a Type 41 naval gun impacting the outer hull/superstructure, then impacting and penetrating the pressure hull, and finally exploding as being akin to the odds of winning the lottery on 2-3 consecutive days. Highly unlikely.

    More likely is a round impacting the main induction valve, and causing the induction lines to flood. As I understand it, even with the hull valves closed, you’re talking taking 16 tons of water on-board. And leaving a significant air bubble on the surface. Happened to at least one other boat…so it wouldn’t be an unheard of event. Cons to this theory; possible evidence of a large sub-surface explosion, and the induction lines aft of the fairwater appear imploded. Still a contender IMO. Maybe the air escaping the induction lines could mimic the appearance of an explosion…

    “made water column”
    “dull water explosion sound”
    “big black-brown water arose”

    To me, this sounds remarkably like it could be the description of a large sub-surface explosion with all the $5 descriptors stripped away. Where’s the official dividing line between a “water splash” and a “water column”? How big is “big”? Do “little” sub-surface explosions have the distinctive “black-brown” appearance of “big” ones (not that I’ve personally noticed, but I could be wrong)? This really doesn’t tell us a heckova lot.

    All the “gunfire theories” blowing up the GRUNION have a couple equally insurmountable hurdles to cross.

    (1) The fact that the round just wasn’t likely to penetrate the pressure hull.
    (2) The puny bursting charge doing fatal damage.
    (3) The Gun-Target Line angle would be something like 1.5 degrees, or an almost a flat trajectory. (gun height above water 11.5 meters, range 400+ meters) To even reach the hull (to penetrate the main pressure hull) would require the GRUNION to be more or less fully surfaced, with decks awash. I think that event would have been noted in the accounts.
    (4) Nothing in the Fairwater to blow up. For that matter, nothing in the accounts convinces me the Fairwater was even exposed.
    (5) More or less, you’re talking an 8cm round with performance comparable to the “Magic Bullet” that killed JFK…after wounding everyone else in the car and doing a few laps around his body. For a round from the KANO MARU to do damage, it had to get there first, and when it did, it had to be capable of doing ultimately fatal damage. Highly unlikely without some truly reality defying behavior.

    At the end of the day, we’re left right back where we started. A PROBABLE large sub-surface explosion of greater intensity than could PROBABLY be accounted for by the 0.75 lbs. TNT equivalent payload of the KANO MARU’s 8cm round. And no “smoking gun” to point to.

    December 14, 2007 | 2:02 pm

    A clarification; Actually, I suspect the “bubble trail” is another translation artifact. What I think Nakagawa is reporting is the same “ripple on the surface”/”washing wave” that Aiura addresses. Somehow it became a “bubble trail”, and someone later slapped the tag on Aiura’s chart as well. It’s (IMO) just the wake of the periscope/shears/fairwater (take your pick) breaking the surface. If you take into account the ship’s heading, torpedo tracks, and adjust for range, it is generally in accordance with the track of the major course change Aiura shows GRUNION making on his chart.

    Nakagawa was a “Medical Sublieutenant”…judging distance/range at sea is most definitely an acquired skill.

    December 15, 2007 | 12:28 pm

    There have been a number of interesting posts by individuals who do not yet have a set of DVDs made from the high definition video of the sub. They will play in almost any DVD player. If you are interested in continueing to help in this analysis send me your snail mail address and I will try to get a set out to you.

    My email is

    December 16, 2007 | 1:01 am

    Having read most of this discussion I would like to add my two bits. While not being a torpedo, artillery, or submarine expert I have to call on my personal experience, High school physics, and deductive reasoning.

    The Torpedo theory first. There would be no reason for the depth to have been set deeper than about 8 feet. If it detonated upon impact or in the vicinity by magnetic means, it certainly would have made a spectacular show as we all have seen from WW2 films of merchant ships being torpedoed. If it impacted without detonation I can recall what I saw on my ship USS Oakhill LSD-7 the last US ship attacked by a Japanese sub in WW2 . It hit and penetrated the closed fireroom which was already pressurized to feed the firebox. I remember seeing a round (about 24″diameter) patch welded in at the point of impact. The stories said there was no damage other than the hole. This patch was still there in 1962-63 ( my days on that ship). This I say may negate the idea of a pressure rise from a mere penetration impact.

    The pics of the open hatch show the latches broken and the gasket displaced. This obviously from internal force ( pressure). The only way this could happen from the bow area is for the control room door being open plus at least one more at the Torpedo room. The control room was still intact while the CT imploded. How did the CT/control room hatch survive? The battery room hatch having the pressure of the water above it and the CT hatch having only the interior pressure of the CT above it. Perhaps the battery room hatch was “backed off” allowing the hatch to accelerate due to the pressure wave before the latches contacted with an additional dynamic load breaking the latches in the process.

    In Admiral Richard H. O’Kane’s book Wahoo, the situation of being prepared for battle surface is described with “amunition train with canned rounds at the mess room hatch” . This by itself does not account for the pressure wave but it supports our systems analyst’s proposal. In another post it is stated that there is an ammo storage space in the forward part which was made into water tight storage when the front gun was removed. What is there to say what was stored in it on the Grunion? Wouldn’t that be up to the Capt? Or the loading crew who always automatically put ammo in it? What if the 8cm round hit this? Perhaps this area could be investigated in the pics.

    It is also mentioned in Admiral O”Kane’s book that the Wahoo made a fast battle surface. ” Four times the normal high pressure air” . Perhaps one of our sub experts could surmise what a hit or a malfunction in some part of this system could do.

    I believe that in order to offer a respectable apprasial, one must consider all of the evidence. I believe that the open battery room hatch is probably the most important part of the evidence. While I cannot offer any reason for the “bubbles” or their “circular track” or any of the rest of the observations,. I certainly will not disparage without good cause, those who witnessed them. I ask those who have the knowledge to support these observations to show how they fit in with the obvious physical evidence.

    Larry Fingar
    December 16, 2007 | 3:51 pm

    The conning tower hatch is intriquing. It seems that it could only have received such damage in one of two ways: If an 80mm shell struck the conning tower and the blast produced such an increase in internal pressure as to blow the hatch upward, partially free of it’s dogs, much as the missing hatches of the USS Scorpion strongly suggest an internal explosion. Or, the conning tower was intact, and sea pressure, as the boat sank, deformed the hatch structure to the point of failure, which flooded the conning tower and prevented any further deformation of the conning tower itself. In my work I have had occasion to bend steel disks by placing them in a vise and exerting pressure on the outer edges. They bend in a manner identical to the hatch. It should be remembered also that the Grunion had a pressure hull made of mild steel. It would react to pressure far differently then the high tensile hulls of the Balao’s and all subsequent classes of US subs.


    Travis Mullan
    December 17, 2007 | 4:56 pm

    I have recently finished reading War in the Boats by William Ruhe which is quite informative. As Torpedo Officer on the Sea Dragon Mr. Ruhe had to deal with a hot fish in the forward room. The outer doors were open during an attack and a bomb from an undetected plane caused the remaining torpedo to partially eject from the tube and begin a hot run. The sub’s motion through the water, with the torpedo projecting from the open tube, armed the fish. The sub was stopped and the motors were run up to full reverse at which point a low pressure shot of impulse air ejected the torpedo from the tube. The weapon detonated two or three seconds after clearing the tube causing damage to the tube doors.

    If this were the case with the Grunion, caused by an exploding shell in front of the bow, a hot run is credible. Also, if the sub were not backed, as with the Sea Dragon, a close proximity explosion could have caused the damage experienced and may account for the pinching of the hull.

    In reviewing video of counter attacks by surface vessels against submerged subs it is likely that if the sub was on her way down, from a broach or aborted battle surface, a hot fish exploding at depth would appear much as a depth charge explaining Mr. Aiura’s account. This would explain the water color and the lack of a water column as would be seen with a torpedo explosion close to the surface.

    I do not agree with the circular run theory as the bow dammage is too symetrical to have resulted from a hit on one side or the other. I believe that if a circular run struck either the port or starboard side in the bow area the opposite side would have appeared peeled back rather than what we are seeing. Mine damage supports this theory and can be seen in many cases of wartime salvage of surface ships. I know that it is difficult to compare the hardened pressure hull of a sub to that of a surface vessel, however, there are few cases of mine damage to subs that are available for examination.

    December 17, 2007 | 10:54 pm

    Frank, Larry,

    The CR/CT hatch was smaller and of a different shape (oval) than those leading to deck. If the hatch dogs were of the same size in all hatches (and being the same mechanism it would make sense being made of the same pieces) the force needed to blast it open would be greater than that neeeded for a circular hatch. I believe this is the reason why that particular hatch could have survived and made the CT implode.


    Although discussions are still very interesting, I believe all these scenarios have been discussed before and each has its supporters. Personally I prefer a circular run with a hit but not an explosion, mainly because I think that Aiura had seen 84 shell splashes and would have been more dramatic when describing the explosion that a torpedo would have produced (assuming the translation is accurate and has not been edited). As Frank points out, a torpedo could pierce through a regular steel plate, I´m not sure about a pressure hull´s plate. But if it could just make a hole, that would be enough.

    An unexploded warhead would still leave the torpedo´s air flask to burst and that could have produced a splash, water would have entered uncontrollably the FTR and finally an implosion would have occured.

    But all these theories are still educated guesses without the key plece: the bow section. From what I know the sonar images don´t show it on the bottom, could it be buried? How far could a submarine like Grunnion have glided away after loosing it and before hitting the bottom? Can it be buried near the start of the path, if Gunnion hadn´t lost it until it hit the bottom? Could it have exploded into so tiny parts that none is visible on the sand?

    We´re all doing our best here, but I don´t think we can make real progress until we can see something of the bow.


    December 19, 2007 | 7:18 pm

    “assuming the translation is accurate”

    It isn’t. I believe it’s extracted from a fluffed up magazine article titled “Submarine Attack”, ghost written by Jiro Kimata around 1962 (I think)…not the actual primary material. You chop out the bumpf and bits where Auira is waxing all lyrical and there’s about half a page of questionable info to work with. Even so, there’s a number of transcription/translation errors embedded in it, without even getting into actual content. Torpedoes spotted at “100 meters” (about 4 seconds out @46 knots) and the KANO manuevers to avoid. Ranges, that are impossible to reconcile. The GRUNION being sunk at 135 degrees to port (neat trick there), ect. Of course, I don’t know squat about navigation or whatever declination factors (or whatever) you’d use up there, so maybe they make more sense to a sailor.

    Bow section; there’s alot that can (possibly) be inferred about the bow from the wreckage. Not that it isn’t all debatable.
    – Section of the forward deck pierced steel decking wedged (last) into the imploded Control Room
    – More forward decking carried aft, deposited (on top) the imploded hull
    – A forward deck access cover lying (on top) the imploded hull forward
    – The bent shears…there’s even a dent in the exposed foot or so of the search scope
    – The forward torpedo loading hatch appears to have been blown clear, or at least open. If so, interesting, since the FTR/FBR bulkhead appears to have imploded forward.
    – The 2x torpedo bodies that popped to the surface (anyone seen the torpedo tail section in the FTR?) in the same general area as the “water column” (note that Nakagawa also calls it a water column on his sketch map). To me, this indicates that whatever happened was catastrophic enough it stopped GRUNION in her tracks, and she appears to have went down almost vertically. I’d speculate the bow isn’t going to be found because it disintegrated, where it separated appears to be a natural fault line/weak point in the hull.
    – What appears to be hull framing/ribs in the rubble in the FTR…this is could likely prove to be the “Smoking Gun” showing the FTR imploded. Unless they came from the FBR area when the bulkhead collapsed into the FTR. Lots of contradictions here.

    Walter Lowman
    December 19, 2007 | 8:23 pm

    After reading and thinking about it, I remembered that most of the air and hydraulic lines run through the top of the compartments. And where are the air bottles for blowing the tanks located? I have served as diving officer on a boomer and firing a torpedo does change the center of gravity. If the diving officer broached, he is then trying to obtain a down bubble.. Planes on dive and more water in the tanks. When the shell hit the boat, is it possible that an air line ruptured or an air tank exploded. A high pressure air leak is very loud and can kill. .If a hydraulic line ruptured and exploded, all in the control room will die. With no control, a heavy boat will continue down, and contact with the sea bottom can rip off the bow. End compartment bulkheads are stronger built than the others to with stand sea pressure. When the forward bulkhead finally gave, the momentum of the incoming water could have blown the hatch off of its seat. The air inside the boat would pressurize and explode providing even more pressure. As for shoddy work, submariners don’t do it. Their lives depended on them doing the job right each and every time. They check on each other all of the time. As for the Mk 14 torpedo. It sucked. It would run up to ten feet below its set depth and the magnetic exploder only worked when it felt like it. It was supposed to arm around 500 feet but sometimes they armed right after leaving the tube. Could one have exploded upon firing? The bow section needs to be found. It would provide a lot of information.

    December 24, 2007 | 1:39 am

    Bob, on your bearing question….Based on 360 degrees referencing on the bow, (my nav background), 135 degrees on the port side would be 225 degrees relative. Some figure it 180 degrees port and starboard, based on the bow. This is obviously the way Aiura is looking at it….Port 135 relative, as opposed to Starboard 135 relative.

    December 31, 2007 | 4:58 pm

    As an Army officer and not acquainted with naval operations whatsoever, I have found and read this blog as a result of reading this month’s article in Reader’s Digest. I have found your suppositions intriguing and highly readable. This is a great mystery with very plausible conclusions. I applaud all of you for the logical progression of your thought processes and the diligence you’ve all applied. I’ll visit this site regularly and believe your conclusions will ultimately help the surviving family members of the Grunion with their struggles to understand what transpired off Kiska in 1942. Keep up the good work and God Bless all who ever wore (or wear) the uniform of the United States’ military forces.

    January 1, 2008 | 2:38 pm

    Jim Christley has put together a pdf file that suggests a plausible hypothesis for the break in the bow. You can see it by going to and double clicking BowBreakHypothesis

    A slight variation of that hypothesis is that the area in front of the fwd escape hatch (because of hydrostatic pressure) was stretched close to the yield point causing crimping and weakening of that area such that when it hit the slope it broke off.

    Because the sub may have hit the slope in a manner similar to a ski jumper the damaged hull stayed in tact.

    January 3, 2008 | 9:53 pm

    All, just returned from a trip and have set up a very nice new computer. Reviewed the DVDs and immediately saw the probable torpedo afterbody in the FTR. (Bob, I did see your power point first, although I have been looking for something like that earlier.

    Bob, some very good posts (1) debris identification, particularly on top of collapsed FBC. (2) Good work on the 8 CM gun and shells and trajectory (don’t know if anyone else is looking at that information) (3) Also good posts on Aiura’s (sometimes self-serving) motivations for comments in his after action report. (Continue to hope that YUTAKA my be able to refine Aiura’s and they other witnesses narrative during his upcoming visit.)

    There is a lot of E-mail traffic out side of the Attack Analysis section of the blog, which is hard to keep track of. Discussions of steel yield strength, bouncy and trim characteristics, etc. With out seeing the figures or reasoning it is hard to evaluate.

    But…I am going to revisit the circular run theory one more time. I use almost daily a formula from ‘Risk Analysis’. The Formula is “RISK = LIKLEYHOOD X CONSECENCES”. Briefly this formula can be used ‘off the cuff’ to plan a work task that will take 5 minutes to accomplish, or used the plan a salvage operation which is 5-6 Volumes of Procedures and will take six months. It is just a case of expanding the data input and justifications. Basically a number is assigned to the likely hood of an event, and also a number is applied to the consequence of that individual event. If during planning the resultant number of RISK is so high as to be unacceptable, the planners go back and lower the likelihood and/or consequences of the event.

    So…the Consequences of a circular run are obvious. In this case they are/were catastrophic (could not be worse) so apply a 10.

    I will make some observations of numbers (and comments) which could be used to enter somehow under the Likelihood field. I anticipate some ‘peer review’ on this and probably some flak. But this is how to decide what happened.

    (1) Grunion fired 6 Torpedoes that day of which 5 were failures in one form or another. This is 83% failure rate ‘on that day alone’. That number increases (in my opinion) the likelihood field. Note: This number is observable both on the day in question and also fleet wide for all U.S. Submarines during the first half of the war.

    (2) Of the 5 Torpedoes which failed 2 of them had demonstrable failures following their path/track. This is 40% of failures were potential circular runs. That number increases the likelihood field. Note: I plotted out the simple geometry for each of the six shots and estimated vessel positions. Simply viewing the plots lead to other questions about relative vessel positions. For instance I noted that the #4 & #5 Torpedoes ran ‘hot, straight, and normal’ to the target but failed to detonate. But…the separation of hits at the target indicated a 3* to 4* degree spread (TDC function / gyroscope controlled). Note: A flooded or flooding gyroscope housing is the most likely cause of a large diameter circular run. This ‘spread’ is a more or less standard spread from the fire control tracking party and noted in other literature of the time. I went back and applied that same 3*/4* spread to #1 & #2 Torpedo spread (i.e., what should have been) which confirmed to me that #1 Torpedo was approximately 12* to 15* to the left of its proscribed track when it passed astern of Kanu Maru. Note: Aiura stated ‘…saw two torpedo track overlapped…’ Note: I concur with Bob on this; Kanu Maru did not have time to effectively change his course to starboard enough to clear that first shot. If you have the actual work sheets of vessel positions and torpedo tracks to look at this becomes more obvious.

    Torpedo #6 had a similar (12* to 15*) deviation (according to a calculated spread of 3*/4* at targeted impact). Torpedo #6 passed astern of Kanu Maru, and Aiura lost all interest in it.

    I assume that there are small mistakes in these calculations, but as in calculations I believe that they ‘cancel each other out’ and the overall pattern is valid.

    So…Torpedo #1 and Torpedo #6 are not running straight, therefore they are on a curving track. Maybe not a steady locked curve, but I assume it is a curve overall. I translated the observed ‘Segment of a Circle’ (this is from known firing position to Aiura’s observed “passed astern”) out into a full circle. It was approx 1000 yards, or something in the order of +3,000 yards circumference. The Torpedo would have had a run time of approx +2 minutes.

    (3) Time Line. Does Grunion have the time to make a 270* port turn (as Aiura’s narrative observed the periscope and subsequent sketch) and arrive back with-in the Projected Circle? My opinion is a qualified yes. The time envelope is there. My question is why? Assuming this was a bow shot, Grunion was way too close to the target and getting closer. Why a Port Turn as opposed to Starboard Turn? But…a hard rudder to Port and full speed on screws would be obviously called for. At periscope depth this Rudder and Power application is the single most difficult operation for the planesman and diving officer to control the trim. These events are 100% of the cause of the resulting broach. (Note: Broaching is a very serious matter if a surface ship or aircraft or other radar is looking for the boat. It is not the end of the world in this case as Kanu Maru already had the boat under intense observation.) One other observation, in this type of turn as the compass reading comes around (the actual turn) it gets faster and faster and is much harder to correct or stop. It is possible that Grunion wanted to come around approx 180* (for a get-a-way) and simply over shot the heading due to the control problem. (For instance if Grunion Sonar knew the #6 Torpedo was still running) The bow and stern planes have much lesser effects during a tight, fast turn.

    (4) Summary: At this instant in the time line: (A) We have a demonstrably faulty, still lethal 6th Torpedo, loose and running in something approximating a circle in the immediate area. (B) We have Grunion smack in the most HIGH RISK area of North Pacific ocean on that morning (C) We have the MK 14 Torpedo which is the only known ordinance in probably +100 square miles which actually has the ‘kick-ass’ to do ALL of the observable damage ALL at one time.

    (5) Is all of this Co-incidence? In my calculation the LIKELYHOOD number of a Circular Run is a pretty high number.

    January 4, 2008 | 12:06 am


    I tend to agree with Jim regarding the separation of the bow, actually I proposed this hypothesis in one of my ealier posts, However I still find it difficult to accept (through lack of evidence) that the control room suffered a shell hit… just too deep at such short range for my liking.

    In my previous post I suggested that an unexploded torpedo warhead might have made a hole in the pressure hull thus allowing an uncontrollable intake of water in the FTR. If this inrush of water was not instantaneous (eg if the warhead made only a small hole-not a full 21in one- and it wasn´t pushed into the pressure hull by hydrostatic pressure, a lot of water will enter throug a hole just 2 or 3 inches wide) probably the FTR could have reached a crushing depth before being completely flooded and so it deformed, as Jim suggests in his sketch.

    What I also see is that, if the scenario of Grunion loosing her bow in this way is correct, is that the bow section is probably under or alongside the rest of the submarine, covered by herself or the sediment that rolled downslope after the hit. That would explain why it is nowhere to be found… even if it desintegrated after a catastrophic explosion, some parts are not likely to have dissappeared, like the anchor and its chain.


    January 4, 2008 | 3:50 am

    All, Here is my take on various questions raised in the recent E-mail. I am having difficulties replying to individuals.

    The reference to “adding/increasing scantling in these areas” as “…scantling is a ship design dimension…such as thickness of a frame”. I believe that the ‘hoop’ type strengthen rings surrounding the FTR escape trunk and torpedo loading hatch are thicker and deeper than those same rings on the remainder of the pressure hull. This would likely be because the escape hatch and torpedo loading hatch required additional support due to their structure presenting an enlarged surface area subject to sea pressure. Looking at the photos and DVD this additional support must be the reason that the structure is still standing. The escape trunk is a stand alone pressure vessel and presents a huge increase in surface area, it would have a much different ‘strain’ effect at its interface with the pressure hull. A ‘proof’ of this theory is in the Conning Tower Hatch.

    I believe the actual structural failure of the Conning Tower was at the inboard edge of the Hatch. As can be seen in photos and DVD the Hatch itself is nearly perfectly ‘cold rolled’ into a ‘U-ish’ shape. This was caused by the ‘dome shape’ to the hatch and to a certain extent the protrusion of the access trunking presenting a much larger surface area than a similar circular area of the pressure hull. I think extreme pressure (whether an explosive event or a crush depth event) subjected to the hatch and trunking caused it to buckle inboard, and it probably suffered a fractured weld at the point the trunking was welded into the pressure hull. The strengthen ‘hoop’ type reinforcing rings can plainly be seen to be distorted. The Barrel shape of the Conning Tower collapsed inboard of the hatch and carried on at the 12 o’clock position for several feet aft. This dimple effect also caused the periscope shears to angle forward to their current position.

    On examining the original photos I believed that this was a ‘crush depth’ event and seems to fit with my understanding of metallurgy. But having now reviewed the DVD and having a good look at the collapse of the Forward Battery, I now believe that this whole sequence of events happened all at one time. The Mark 14 Torpedo did have the explosive ability to accomplish all of the damage that I can see.

    This Torpedo exploded just above the port bow plane and punched a hole into the port side just below my old bunk. The DVDs (as opposed to the still photos) show a portion of the hull approx 4 feet folded straight in. The starb’d side shows essentially superstructure sheet metal to be folded (pinched?) toward the port side. Note: The photo of Growler bow shows how all of the superstructure (included bow buoyancy) would fold up if it was hit from the port side. The entire Torpedo Room (from WRT tank forward) fell down and slightly to port due to the force on the port side. It was not supported by water at this instant; there was a large hole in the water of expanding gases. Any pressure hull remaining tore or fractured along the reinforced ‘hoop’

    I think I counted 10 Torpedo skids or the remains of 10 skids the last time I looked. The skid which is most noticeable (sticking up from the center of FTR) appears to be the uppermost of the debris pile. It probably started life just under the bunk (still visible through the crack in the dished hull) the skid to bent nearly into a ‘U’ shape from force applied from the port side. The debris pile also has several of the torpedo loading skid ‘beams’ (which allow the torpedoes and their skids to be positioned) which also show similar damage. The torpedo room was likely fully rigged with these beams in position for reloading operation. I do not see how simple contact with the sea-bed could do any of this damage.

    Last thing on this post. Grunion was operating at near zero buoyancy, with a center of gravity approx at control room (read negative tank). The FTR disappeared in an instant with its 10’s of tons of equipment. Not very long after that event the boat had to settle by the stern and probably sank nearly vertically. (Thin bar falling over). I think a case can be made that the Forward Battery (imploded 12 o/c) and Conning Tower (imploded forward end 12 o/c) were also flooded at this point and probably Control Room (collapsed FBC bulk head) and After Battery (due to the Hatch opening due to differential pressure from expanding explosive gas bubble).

    The reported fuel leaks came to surface as result of vertical descent, and keel fracture noted in the area of negative tank / control room.

    Robinson Brigham
    January 6, 2008 | 5:00 am

    IAfter I reading the mystery at sea on the Readers Digest on page 116 ,I thoug it was very interesting article, specialy becouse I was born in 1942,I spend some time working on merchan marin,I Think the comander of the Grunion underestimade The Kano Maru Sk.

    Travis Mullan
    January 7, 2008 | 4:59 pm

    I believe that the diagrams on the web site: will be of assistance to those of you attempting to make heads or tails of the wreckage along the upper portion of the Grunion’s hull. There are numerous diagrams delineating the different systems (main induction, high pressure air, hydraulic, etc) found there. As many authors have stated while writing about these boats “there is a maze of pipes and valves hidden under the decks and throughout the hull”. Truer words were never spoken and to analyze this “maze” in its current condition is a daunting task at best. Good luck.

    January 10, 2008 | 11:37 am

    Hi Ed! Nice to see you back.

    Risk Analysis…You won’t get any flak from me. I used a Threat weapons severity/probability Matrix, and sent Bruce the crayola version using flow charts. Same difference, same results.

    Torps 1/1 and 1/2; This revolves around the transcription error with the range the torps were spotted out. At 1 klick there’s the chance KANO got her butt around. Shorter range, it’s unlikely, and torp 1/1 (aimed forward of bridge) missed astern.

    “Why a Port Turn as opposed to Starboard Turn?”; Because a starboard turn would have taken GRUNION right under the KANO’s stern.

    “if Grunion Sonar knew the #6 Torpedo was still running”; Unlikely IMO. At 0607 when GRUNION fired the last salvo, torp 3/3 would have been completing the loop astern and lost in GRUNION’s prop noise. After making the 180 course reversal, she’d have left a big knuckle in the water, would have just been clearing it at 0610, and was undoubtedly making alot of noise adjusting trim.

    Any way to SWAG the KANO’s rate of deceleration and drift? Or figure an approximate residual forward speed for KANO at the various time hacks? This is also key to clearing up the attack plot…

    January 22, 2008 | 2:20 pm

    Attack Analysis Methodology

    Some of the analyses that are going on are problematic because there is not clear agreement on the methodology of determining a credible hypothesis. I think everybody’s time will be used more efficiently if we spend a few minutes thinking about that methodology

    Our objective is to find a credible hypothesis for the loss of the Grunion.

    I would start with there is no complete or absolute credibility. Credibility comes only from a stream of consistency. The longer the stream (with out inconsistencies) the greater the credibility.

    Consistency is learned associations. There is nothing magical or “true” about those associations. A child that over and over watches Dumbo the elephant fly will hypothesize that elephants can fly. An engineer who has learned that the buoyancy on an object is consistent (equal to) with the weight of the displaced fluid will consider that a credible hypothesis. Winning is consistent with the Patriots.

    Credibility is not a state of the real world but a state of the mind. What is credible to one individual may not be credible to another. Likewise consistency is not a state of the real world but a state of the mind.

    Therefore I think this methodology requires that we decide whose minds have to be convinced. I would argue that it should be a group of individuals with at least the following characteristics:

    o Submariners, or those with excellent knowledge of subs

    o Independent thinkers, not prone to go along with the crowd

    o With enough interest, enthusiasm and energy to thoroughly study the situation

    o Knowledge of submarine physics.

    I would also argue that selection should be natural, ie those who want to be part of and will contribute significantly to the process. No dictators for the selection.


    There are dangers in starting the analysis with hypotheses that are all encompassing or hypothesis of complex transformations. Because of that complexity it is very easy to miss inconsistencies. In addition it is also easy to get attached to one’s hypotheses and then ignore or skip over the inconsistencies. That process of ignoring inconsistencies I label “neurotic censorship”. It is very common.

    For these reasons I think we should start as much as possible with elemental hypotheses, hypothesis of simple transitions or patterns. Then we should generate an organized list of those hypothesis that have enough credibility that investigating them is no longer worthwhile. In the vernacular we call those hypothesis with high credibility “facts” meaning only that we will not spend more time investigating them, and that we “believe”, that we “know”. We are saying that (for us) the stream of consistency for those is long enough to have passed the threshold of believability.

    Here are some elemental hypotheses where the credibility (for me) is high enough to be labeled “facts”

    It is the Grunion
    There is hydrostatic damage to the hull
    There are several cracks in the upper part of the hull
    The superstructure is almost entirely gone.
    The AB Hatch was blown open
    There is crimping around the bow. The bow is gone.
    ET is a holder for insulators
    There is hydrostatic damage to the conning tower.
    The loss of the sub was the result of a very complex transformation
    The 84th shot had something to do with loss of depth control.
    The sub was close to the surface, or was surfacing, because of operational problems.

    Once we have developed this list of “facts” we can get into the all-encompassing-hypothesis
    mode submitting them to our “heavy hitters” to see if discrepancies can be found.

    That process (using the heavy hitters) actually will provide a measure of credibility. Unanimous agreement indicates high credibility. 50% indicates pretty low credibility

    The methodology being described here is, of course, itself a hypothesis and will only be credible for those individuals who have checked (thought about it) and found with it a stream of consistency.

    We are fortunate in this situation because we are not locked to any administratively determined methodology for determining credibility, such as a jury system, a board of inquiry, or peer review as used in academia and in the medical field.

    We can choose the methodology that will come up with a hypothesis that over time is most likely to extend that stream of consistency. That is what the methodology of science is all about.

    It is an exciting opportunity.

    Terry Terrass
    January 28, 2008 | 6:30 am

    27 Jan 2008

    Hypotheses for Loss of Bow

    One theory advanced for the loss of the bow is the explosion of a circular run torpedo. In my opinion past postings from a number of sources provide a variety of reasons to reject this theory.

    In lieu of this theory, based primarily upon the location of the break as shown in the sketches by Jim Christley, I am now inclined to believe that the bow was lost as a result of the dynamic forces experienced during the descent to the bottom. The portion of the pressure hull near the break had a number of penetrations. The largest, and the ones I believe most significant, were those to port and starboard for the shafts to tilt the bow planes. As best I can determine the next largest penetrations are the two extending upward into the superstructure, one for bow plane rigging and the other to drive the anchor windlass and capatan. In addition there are several other smaller penetrations with shafts for controlling windlass/capstan (and perhaps other) functions from topside. I believe that the combined effect of these penetrations resulted in the hull being less able to resist stresses caused by depth increases in this area than in portions of the pressure hull without these discontinuities.

    Even more significant than the stresses resulting from increasing depths, in my opinion, are those which were very likely to have been caused as a result of the bow planes being rigged out. The large surface area of the planes, when combined with a sinking velocity much higher than designed service speeds, could produce a total force much larger than what would be experienced when conditions were normal. On the assumption that the ship was trying to surface immediately before it was lost, it seems most likely that the bow planes were on “full rise” while the ship was sinking and, if so, the dynamic forces would have caused the hull to start rupturing on its’ under side as a result of tension. It is felt that the possibilities of rupturimg in the oppositte direction or with an axial twist would be much less likely.

    Between my poor skill in anayzing the photos and only limited time for trying to do so, I leave it to others to see if there is any indication of the validity of this hypothesis.

    The after portion of the Forward Torpedo Room could be another area particularly prone to stress failure because of its configuration with both the torpedo loading hatch and the transitions with the Forward Battery compartment bulkhead and No. 1 Main Ballast Tank. Perhaps this is the reason for the “major structural break” indicated by Item #3 on the Christley sketch. Here, without the forces caused by the bow planes, there was a break but no separation.

    Terry Terrass

    February 3, 2008 | 10:41 pm


    If the bow section was in its place during the sinking, certainly the bow planes would have behaved as you suggest. But, the links of those to the rest of the hull structure were just steel rods, designed to sustain the stress at, probably 12 to 15knots (ths sub´s max submerged speed was 10), so I believe that they would have been torn away before they could have caused any damage to the pressure hull.

    You mention the cracks in the forward section, and the hull rupturing from below. I don´t think this would happen: the pressure hull was the same thickness both up and down, so I don´t see why it would break near the keel first (of course it had to break somewhere first) but, precisely, the keel should have acted as a reinforcement to the structure in that place. In the upper portion, however, there were no longitudinal strength members (someone correct me if I´m wrong, this is important), so the weakest point should be in that area.

    BUT, carrying on with your analysis, and taking your observacions a little further: there are cracks both fore and aft. Do they look the same. NO. Cracks fore have there edges bent and the hull seems disaligned. Cracks aft have prefectly flat edges, and the plates have only separated, no misaligment here. My conclusion is that the cracks towards the bow were caused be compression of the upper pressure hull and the ones aft by traction forces.

    How could this have happened? If Grunion hit the bottom bow first (with of without the FTR still attached) the front end would have been bent upwards, causing cracks near the deck. When the aft portion of the boat hit the bottom it must have suffered a “whip” effect (remember that crush depth had been passed long before so probably these compartments where also flooded) and produced the cracks with clean edges, just tearing the plates appart.

    Further clues (don´t dare to call them evidence) to a bow-on impact:

    Absence of damage to stern (not even bent prop blades)
    Periscope shears bent forward (if attack periscope was still up it must have “whipped” too, the force being so strong that the mast broke appart and now lays across the deck)
    Gun pointing upwards. It has been suggested that the whole pedestal in the wrong position, as if laying on deck, but if you look at pictures of similar guns you will notice: gun barrel and layer´s seat should be parallel (they are not) and trunnion support structure should be perpendicular to barrel (they are in the same line). Besides, the small elevation gear that worked with the large one under the barrel is missing. So the barrel is free in elevation. This damage could have been caused by the large gun´s inertia when hitting the bottom.

    So, you see, we have both looked at the cracks, just got different interpretations.

    Terry Terrass
    February 9, 2008 | 9:11 am


    Guido –

    Here are some comments relative to your response to my “bow plane hypothesis” posting.

    There are several references below to John Alden’s book “The Fleet Submarine in th U.S. Navy”. They are not .specifically applicable to the GATO class but are probably applicable to at least some extent.

    I mentioned the shafts for the bow plane rigging and the windlass/capstan not because of whatever effect they may have had by themselves but because of the contribution to pressure hull stresses which may have been induced by their hull penetrations. Reference page 17 states ”…deficiencies were discovered in the longitudinal strength of the F-4 and F-5 hulls and there were local structural weaknesses around the escape trunk and windlass room above the forward torpedo room. The upper part of the pressure hull had to be increased from ¾ inch to 1 inch plating in some places, along with other design changes … “. There was no mention of keel strength.

    I have several problems with the way you characterize the pressure hull in the torpedo room. First, the hull in the torpedo rooms is “single hull”, not double hull like the other compartments. Secondly, and perhaps more important, besides being single hull the torpedo rooms do not have the circular cross-section of the other compartments. The bottom of the FTR consists of large flat horizontal plates. The center portion of these plates form the bottom of the lower reload torpedo pit while the higher horizontal plates extend outward from the top of the pit to the pressure hull. This arrangement is pictured on page 215 along with sketches showing the differences in the Electric Boat and Portsmouth designs for framing in the non-circular hull sections. The lower/outer side of these plates is subject to full sea pressure in the underlying No.1 Main Ballast Tank.

    In the discussion of hull strengths and the need for circularity the following quotes from pages 16-18 may have some applicability to an explanation for the loss of GRUNION’s bow:

    “ … the greatest hazard is local structural failure at a so-called “stress raiser” – a place where a hard spot, discontinuity, or flaw in the structure causes the stress to be concentrated. As their understanding of these factors grew, submarine designers and builders tried to avoid abrupt changes in the shape of the hull and to maintain perfect circularity of the cross-section wherever physically possible”.

    On page 215 there is a note on the sketch of the Electric Boat design for the framing of non-circular single hull design which says, in part “The larger bending moment gives a stress to be added to the P/A stress. By trial and error scantlings are increased as necessary to reduce stress to an acceptable level.” (I assume that P/A means ‘pressure/area’)

    As an attempt at a “bottom line”, even though the forward torpedo room is designed to withstand the same submergence pressures as the rest of the ship, I doubt that it has the same inherent safety margin as the other compartments with their circular hull sections. I do not know how to quantify this but think that the typical slight “dishing” of the pressure hull between the frames in the circular hull sections illustrate my contention that hull strength is less in the torpedo rooms than elsewhere. Likewise, because of the different configuration, my intuition tells me that there could be greater stress concentrations in and around the torpedo rooms, whether caused by submergence pressure or dynamic forces, than those in the circular hull sections. Beyond that, if the basic design process required trial and error, it is unlikely that there would have been much, if any, analysis of abnormal contingency situations which might have been experienced by GRUNION.

    Given all the variables of hull strengths and stress concentrations I will not hazard a guess as to just what caused the various indications of damage which have been observed.

    Likewise I would not hazard a guess as to what happened to the deck gun although it must have been quite severe.

    The situation is somewhat different for the periscope shears. Based upon pictures I have seen and stories I have heard about boats getting hit by surface ships it appears that it does not take all that much force to bend the shears over, especially when one considers that they represent a long lever arm. Perhaps, as a contrary view, is the experience of USS IREX (SS 482), a Fleet Snorkel boat, after getting a new fiberglass sail. In February 1960, after a big ASW exercise in the very rough seas of the Greenland-Iceland-UK gap my boat passed IREX which was then enroute to a port visit in Belfast, Ireland. IREX looked weird – the rough seas had knocked off the entire fiberglass sail so that all we saw was the periscope shears but they all looked upright and intact. Back in port she got a new sail but I never learned any details about what had happened although I am surprised that the periscope shears would not have suffered extensive damage. I think that I did hear, much later, that larger and stronger fasteners were used for the replacement sail.

    Post Script
    After preparing the above I went back and reread your comments, and specifically those which stated “….the keel should have acted as reinforcement to the structure in that place.” When I had first read those words I was inclined to agree but then decided that I had better learn something about the keel. When I could find nothing about keels in my reference books, I went on the Web. I could find nothing definitive there either.

    Failing in that attempt, and at the risk of being very wrong, the views which follow seem to be consistent with what I can remember.

    Rather than the keel in a GATO class sub being a longitudnal strength member as you imply, I now think that the term “keel” refers to a location at the bottom of the ship, mostly in the bottom of a tank, rather than a part of the hull.. I am not sure that there is a keel structural member as such but if there is one at all I do not believe it is a major strength member. For the compartments between the torpedo rooms I believe that the double hull construction provides the strength which comes from the keel in surface ships. There are vertical plates in the bottoms of the ballast tanks which are located where I would expect to find a keel. I would not consider them as serving the function of a keel since they seem to be relatively thin and intended primarily to hold the outer hull to the pressure hull. If this is correct they would not need to be thick and strong since the outer hull does not have to withstand full submergence pressure.

    Although my view may seem inconsistent with the mention of a “keel” in the following quote from the on-line version of “The Fleet Type Submarine” I think that my view is basically consistent with the actual construction features and the relative lack of hull rigidity.
    (Start of quote)
    The construction of the submarine, therefore, is on the basis of the fabrication of a series of watertight containers into one large watertight cylinder by means of watertight joints. However, since the submarine must operate at times at great depths, these watertight containers must be strong enough to withstand the pressure head of sea water at that depth. Therefore, the watertight containers must be pressure vessels, that is, watertight containers or cylinders capable of withstanding great pressure. The fabrication of these containers into the hull of the vessel is illustrated in Figure 1-11.
    Pressure vessels, while capable of withstanding great pressure, do not in themselves possess great rigidity. Being subject to mechanical action (leverage), they must be secured to each other by one common strength member (the keel), as well as by watertight connections (bulkheads). The submarine with its keel, pressure hull, and watertight bulkheads is shown in Figure 1-12.
    In the double-hull type of submarine, the pressure hull is inside the outer hull; between the two hulls are the water and the fuel oil tanks. The double-hull construction extends from the after bulkhead of the forward torpedo room to the forward bulkhead of the after torpedo room. (End of quote)

    In my view the keel, whatever it is, plays a minor role in holding the compartments together; primarily this is done by the watertight connections (bulkheads). Although a substantial keel might have prevented the loss of GRUNION’s bow, the cumulative experience of the GATO class would seem to indicate that it was not necessary.

    Terry Terrass

    Travis Mullan
    February 11, 2008 | 4:56 pm

    Further to the discussion on the effect of excessive pressure on diving planes please see the following:

    April 5, 1945 at 1525 the bow planes on the USS Spadefish were unintentionally rigged out while at flank speed in rough seas.

    The stbd rigging gear was carried away immediately. Also, the universal joint was fractured.

    The collar on the horizontal shaft sheared off at the drift pin.

    There was no damage to the port side diving plane.

    There was no damage to the hull in way of the shafts for rigging or actuating the planes.

    The crew was able to make temporary repairs although they failed later in the patrol.

    Permanent repairs were made at Guam at the end of the patrol.

    For ballast tank arrangements see ——-
    Line drawing of the General Arrangement of the Gato (SS-212) class, main and fuel ballast cut out.

    You will see that the Number 1 main ballast tank is in the after portion of the Forward Torpedo Room. The tank top serves as the deck in this area. The bow of the Grunion broke off in the “pit” area a few feet forward of the number 1 tank.

    February 14, 2008 | 5:18 pm


    Something as obvious as the MBT1 forming the deck of the FTR I completely missed. The only sources I have are cutaway diagramas and I simply undestood that the ballast tank form I could see didn`t represent its complete form, and that it was round. Certainly I would have never thought of leaving a flat surface exposed to sea pressure. A terrible mistake on my side.

    Taking that into account I have also some comments, for which I hope you´ll be able to send some feedback.

    Regarding the safety margin, I believe it is called the “safety factor”. That means that the crushing depth must be equal to the max diving depth times safety factor. (A safety factor of 2 in a design for 300ft diving depth implies a crush depth of 600ft). It is also spplied to the whole submarine and not to individual compartments, as it is meant that none of them will implode at any shalower depth. After that, one compartment may be stronger than others, but that`s a plus.

    The flat top of MBT1 puzzles me a little. You mentioned “stress raisers”, and certainly the anlges around the pit worked as such. But the tank top is not even distorted, and the implosion occurred around the pressue hull (very close, I think, to the penetratrions you mention for the capstain/windlass). Even more, the top of a small tank that was immediately fore of MBT1 is still there, completely flat, but the tank is gone. What kind of tank was this?

    About the keel: I`m not that proficient in English to know the word for the lower part of a tank. But I do concur with the quote from “The Fleet type submarine”. However, the keel is not just a piece of steel In many cases it is a structure, the objective of this is to achieve greater strength using relatively thin plates. In many cases it will take the shape of a long box. Many (not all) of the side tanks were divided in port and starboard, so I suppose that a solid piece of metal separated both at the bottom, that would be the keel. Also remember that subs were intended to “bottom” and a substancial structure should keep the lower portion of the outer hull to crush, as well as during dry docking.

    Your posts made me realize that me thesis that a dud had hit Grunion and that the “black water column” was a product of the torpedo`s air flask explosion is wrong. The forward-most fuel tank is still further aft of MBT1, well clear from the missing bow, so it could have not been damaged by a dud torpedo.

    But I`m still against a direct hit, as this should have hit exactly at the same frame where the reload torpedoes warhead would have been. This wuold have set a chain reaction and the reloado torpedoes would have exploded as well, but the damage to the submarine would have been much more extensive.

    Furthermore, alll imploded compartments did so along there top side, but the FTR shows signs all around the hull, except at the bottom, which you would expect to be the weakest point especially after the design around the hull penetrations had been modified. Did the FTR implode above (shallower) crush depth? That would be a clue to that it was damaged before getting that deep.

    Travis`post makes me believe that the bow planes didn`t do any damage to the pressure hull, in the worst of cases they were torn away or distorted.

    But then, what caused the sinking? Did the shell hit the FTR? If so, why did it implode? It should have been flooded.

    I think I´m more or less where I started, but as interested and intrigued too!

    Terry Terrass
    February 16, 2008 | 7:42 am


    Travis Mullan –

    Here are some comments relative to your information about SPADEFISH and her unintended bow plane rigging incident.

    I question what inferences applicable to GRUNION can be made from the SPADEFISH experience given the following.

    SPADEFISH was a “thick skin” BALAO class boat whereas GRUNION was a “thin skin” GATO.

    Presumably the SPADEFISH bow planes were in the “15 degree dive” position normal for surface running rather than “full rise” which was probable for GRUNION given its circumstances. This would reverse the direction of the forces acting on the hull. (Note: Rigging in the planes at 15 degrees dive, rather than at zero, to decrease diving time, was a modification phased in as the war progressed but was undoubtedly incorporated into SPADEFISH during construction.)

    Depending upon how far the bow planes had rigged out by the time of their failure an analysis by resolution of forces would indicate that the magnitude of the forces tending to move the bow vertically would be less than if they were fully rigged out.

    The force exerted on the hull by the planes, whatever their position, would be affected by the speed through the water. Even with a flank bell rough seas might keep velocity less than would be expected normally. Beyond that, while I do not really know, I think that conventional wisdom contends that velocities reached while sinking to the bottom can be quite high.

    I have not been able to find enough information about the rigging mechanisms to form any opinion as to just what SPADEFISH parts may have failed or the effects of those failures. I am surprised that the crew would have been able to effect any repairs, even temporary ones. Likewise I have been surprised by the number of times that bow plane rigging problems have been mentioned in my various readings. These mentions have not included any elaboration beyond indicating that the problem was repaired.

    Predicting just where and why rupture would have occurred in any single hull, non-circular hull.section is too difficult to be meaningful because of the number and complexities of the design, construction, and environmental variables which might be meaningful. This seems to be particularly applicable to #1 MBT and adjacent structures.

    Where Is the Bow?
    To the best of my knowledge this is still a mystery. As a far-out speculation I will mention a possibility I saw on a TV program with a variation on the UFO theme. It was about unidentified submersible objects. I don’t remember its title but think it was on the History Channel. The part that caught my interest was a search for a light plane which had crashed some years before in the channel between Catalina Island and the Southern California coast. Notwithstanding what was considered to be reliable evidence of where the crash had occurred, divers were unable to locate the wreck. One theory advanced as to where to continue the search was that sea action, over time, would probably carry a relatively light object such as the plane further down even a fairly gentle slope. Given the characteristically rough Bearing Sea conditions and the depth at which the GRUNION hull has been located, is it possible that the bow lies further down slope? To what extent was this area explored during the searches made to date?

    Terry Terrass

    Terry Terrass
    February 18, 2008 | 8:47 am

    17 February 2008

    Guido –
    Several comments relative to your posting of February 14, 2008.

    The cutout drawings are useful for many purposes but fall short when trying to answer certain questions. This is especially the case for trying to understand the Forward Torpedo Room.

    Relative to the “safety factor”, at least as I think it was used for the design of GATO era submarines, it was not used as a design objective but rather represented a minimum acceptable criteria for the whole submarine and all of its component compartments and structures. Whether by choice or by circumstances, many submarines took advantage of the fact that the actual design was much more conservative than called for by the “safety factor”.

    Maybe it is just semantics but I do not believe that the FTR “imploded”. I am more inclined to believe that the bow broke off due to the differences in forces acting on it as compared with the forces acting upon the hull further aft with the location of the break being determined by where the stresses were greatest.

    The small tank forward of #1 MBT is the WRT (“Water Round Torpedo”) Tank. I think that it was designed to withstand full submergence pressure but would normally be vented to the FTR except when being used to flood the torpedo tubes. I do not understand what you are saying about the top being there but the tank being gone.

    The vertical plates at the bottom of the hull sections come closer to serving the function of a keel than of being boundaries between the port and starboard side tanks. For the MBTs the port and starboard tanks are effectively interconnected by having open flood ports. For the fuel tanks the port and starboard tanks are interconnected by openings in the vertical plates so that only one compensating water line is needed. The distinction between the port and starboard sides comes from what occurs at the upper end of the tanks. For the MBTs the port and starboard tanks need to have separate piping to vent the air to submerge the ship. The fuel tanks need to have separate fuel filling and transfer line connections to the tops of the port and starboard tanks since the fuel rises to the top of each tank.

    The strength of the keel, whatever the keel is, is much more important for drydocking than for bottoming the ship because in drydock it has to support the full deadweight of the ship. For bottoming it only has to support the negative buoyancy which is minimized for a variety of reasons.

    Please see my posting responding to the posting by Travis Mullan relative to the role the bow planes may have had in the loss of GRUNION.

    As I have stated before, and continue to believe, GRUNION sank as a result of the cumulative effect of flooding in several locations, most significantly in the Forward Torpedo Room through one or more torpedo tubes and in the Main and Engine Air Induction piping penetrated by KANO MARU shell hits. As I have stated before I believe that many of the 84 shots fired by KANO MARU landed in the water and continued on with enough velocity to cause significant damage by their impact even though they did not hit with enough force to cause detonations which could have been seen by observers on the maru.

    Terry Terrass

    Travis Mullan
    February 19, 2008 | 7:04 pm

    The question raised by Guido of why the ballast tanks were not imploded has only two possible answers. The first answer being that they were damaged and became flooded preventing implosion. This is highly unlikely since all would have had to have been damaged individually. The second answer is more interesting in that they were most likely flooded for the initial dive and equal to the surrounding sea pressure while the Grunion was submerged. This would mean that the Grunion was not surfacing when the Kano Maru made the final shot from her 3” gun. An earlier posting stated that Commander Abele was probably encouraging his diving officer to counter a broach and get the boat back down. This is most likely correct. Remember that the Kano Maru had been firing steadily at the Grunion during the attack and the Commander must have been aware of this through his periscope observations and reports from his sound man. I can not think of a reason why he would voluntarily surface his boat under the gun of an enemy. Evidence of the ballast tanks being flooded is found in the intact appearance of the #1 ballast tank in the FTR and in other areas of the hull. The outer portions of the sub, visible to the observer, are the ballast tanks. The pressure hull lies between the crescent shaped tanks and serves as the inner side of the tanks. On the Grunion today, the tanks around the control room and crews mess room seem to be intact along with the pressure hull. In areas of the hull where the pressure hull imploded the tanks have been distorted only at the top. There are cracks in some of the tanks which are likely due to implosion induced stress or impact with the bottom. This would indicate that these tanks were flooded.

    Another item observed in the photos and video is that the main induction piping does not seem to have imploded. There are many breaks at the flanges, however, I was not able to see any distortion of the piping. It is possible that the main induction valve, housed in the after portion of the conning tower fairwater, was damaged by shell fire. The starboard side of the conning tower seems to have been damaged significantly more than the port side. The starboard side of the Grunion was presented to the Kano Maru over the majority of the attack while the port side only at the end. There are many other accounts of American subs being fired upon while at periscope depth but reporting no damage……

    Lastly—the reference to the Spadefish was only as a reference with the differences in construction well understood. There are few reports available outlining the damage caused by inadvertent out-rigging of the forward planes at speed. Another 2 cents worth.

    Terry Terrass
    February 25, 2008 | 9:00 am


    Travis Mullan –

    Here are some comments relative to your posting of 2/19/2008 re imploding of ballast tanks.

    I assume that the term “imploding” implies that the tank ruptures as a result of excessive differential pressure on the tank boundary rather than being subjected to external forces such as pressure hull failures.

    Given that the ballast tanks have flood port openings close to the keel there is no way they can be subjected to static differential pressures exceeding the difference in sea pressures between their upper and lower volumes, about what they experience when they have been blown for surface running. Transiently they could experience higher differential pressures while there is flow through the flood ports but this would be for a very brief period and with a relatively small pressure difference.

    The statement is made that “Grunion was not surfacing” because the tanks were undoubtedly flooded from the initial dive and were equal to the surrounding sea pressure. Had the GRUNION been trying to surface they would have blown the tanks with their normal ballast tank blow system and the tank pressures would still equal the surrounding sea pressure.

    I think that it is quite likely that the water column which was mentioned in the KANO MARU report resulted from the hit by the 84th shot releasing whatever air was in a ballast tank, either by penetrating the outer skin of the tank or, less likely, by rupturing the vent piping between the tank and its vent valve. The decking would tend to break up the air column if it came from the vent piping.

    The point has been made previously, by both me and others, that GRUNION was probably trying to surface, not because it wanted to but because it seemed necessary in order to keep from sinking.

    Although I am confident that the ballast tanks did not implode because of differential pressures I think that it is quite likely that they could have been damaged and/or distorted by the implosion of nearby pressure hull compartments.

    Terry Terrass

    February 26, 2008 | 7:41 pm

    Hi Terry, sorry for the delay.

    Thanks for the explanation about the “split” fuel tanks. Openings in the keel structure could be made for different puroposes without lessening its strength. Of course it would have to bear more weight when drydocking, but in that case the weight distribution would be more or less even, as the wooden blocks under the hull must be at the same height. However, I think that when bottoming, the bottom´s shape or just a rock may result in an uneven surface and thus greater local stress than in drydocking.

    About the Water Around Torpedos tank. As far as I can see from the schematics on navsource (check Travis Mullan`s post regarding this source) the floor of the FTR was formed, from stern to bow, by the top of MBT #1, Water Round Torpedo tank and Trim Tank#1. In the photos of the “pinched bow” you can see the front end of MBT#1 and a horizontal deckplate forward from it. This would be the top of the WRT, and you can see the beams underneath it. But the tank´s sides and front are missing completey. There`s no sign, that I can see, of the Trim Tank.

    I`m not sure either tha the FTR imploded, but I can`t dismiss it completely. All other (visible) comparments imploded along their upper side, but the FTR didn`t. Actually the remaining upper side between the fore Battery bulkhead and the escape trunk is intact. If there was an implosion, it was a radial one, pinching the round pressure hull but not its flat bottom.

    The flooding theory doesn`t convince me yet, as it would reduce the differential pressure and the risk of implosion. The flow of water through either a torpedo tube or a shell hole can be easily calculated, and would result in a complete flooding after a few seconds in the first case and maybe a minute in the second. There have been some posts regarding floodings along the discussion.

    I would like to ask you a couple of questions regarding the induction and exhaust pipes, for your observations are very interesting:

    I`ve seen a picture of the main induction valve with a piece of metal sticking out of it. This valve should have been shut, can you see if it is in the open position?

    Also, if the pipes had been damaged, there would still be the hull exhaust and supply valves, also in the shut position. The aft compartments are imploded so they were not flooded; what would have been the efect of the flooding of the pipes only? Stern heavy, up bubble, broaching? Could this have left a trace of bubbles on the surface, looking like a torpedo`s wake?

    Even answers to this wouldn`t solve the mistery, but at least would explain a couple of minutes of the story.
    Travis Mullan navsource

    Travis Mullan
    February 29, 2008 | 7:29 pm


    Check the following link for construction details of Gato boats:

    The following boats list construction, etc in their image links:

    SS 283 Tinosa construction
    SS 266 Ray construction
    SS 270 Raton construction and shows a fleet boat surfacing. Looks like the bow was up before the shears.
    SS 266 Pogy construction
    SS 258 Hoe under deck repair—good exhaust and induction shot.
    SS 239 Whale keel
    SS 237 Trigger keel
    SS 236 Silversides main induction
    SS 226 Corvina torpedo hit
    SS 259 Jack torpedo hit

    Hope this helps.

    March 19, 2008 | 1:00 pm

    The report from the 2/27th New London meeting can be seen at in the Grunion folder. Select Hypothesis Report.pdf.

    Christley, Thompson and Galler have provided a very objective analysis of what we know today about the loss of the sub. It is worth studying carefully.

    Tom Rabil
    March 21, 2008 | 7:05 pm

    Having seen the Jonas Ingram be torpedoed, I would expect the explosion to have been significantly greater.
    If the sub was preparing to surface, it would have gotten the diesel ready and opened the exhaust and induction valves. If anything happened in that critical transition period, the sub would have had little speed capability and been much more vulnerable to flooding from a smaller shell hit. Also, if a ballast tank was breeched, there’s that much less buoyancy available for recovery.
    If the sub went down nose first fast, taht could account for the damaged bow.

    March 29, 2008 | 1:12 pm

    I have reviewed the Sinking Hypothesis Report from the Christley, Thompson ,Galler meeting of 2/27/2008. I agree with their report in many respects, most significantly that it is highly improbable that GRUNION’s own torpedo caused her loss.

    I do have a number of comments that I believe warrant consideration. Their objectivity stems from several factors:
    1. My 18+ years of submarine experience on seven different submarines, five being Diesel. including USS CAVALLA (SS 244). GRUNION and CAVALLA were built at Electric part of the 1941 Construction Program with commissionings in April 1942 and February 1944 respectively. Although both boats were GATO’s CAVALLA incorporated some improvements resulting from wartime experience.
    2. Pasr personal contact with a number of WWII submarine commanding officers.
    3. Research based upon several detailed submarine books

    In my opinion the most notable omission from the Report is the highly probable flooding of the Forward Torpedo Room, a hypothesis I have tried to advance for some time. Mike McMahon in his E-mail of 3/22/2008 described the event as follows:
    “I think that a possible flooding in the Forward Torpedo Room during reload should be
    added as a possible cause. It is extremely likely that, after the
    expenditure of all 6 torpedoes loaded in the forward tubes, a reload
    of some of the remaining 4 torpedoes was started. We know from
    message traffic that there were no torpedoes remaining aft, and that
    Grunion had been depth charged the day before. We also know that Tang
    had a flooding casualty in a torpedo room later on in the war caused
    by depth charging. The inner and outer doors are interlocked but that
    does not prevent flooding as Tang demonstrates. If there were a
    severe forward flooding, that would explain an attempt to surface.
    Flooding in the Forward Torpedo Room would result in a heavy overall,
    heavy forward condition leading to a sinking by the bow. Finally the
    bow is broken off from the collision with the bottom.”

    Although not mentioned in the Hypothesis Report or by Mike, I believe that the bubble path observed by the Kano Maru after the 6th torpedo was fired is a very significant clue as to the Torpedo Room flooding, even though it has led some to erroneously hypothesize a circular run.. I believe that the bubbles came from air leaking past a torpedo tube muzzle door which was kept from closing tightly by the deformed door gasket while the tube was being blown down preparatory to reloading.
    Although blowing down the tube does not necessarily indicate that a reload was being initiated, there are reasons to believe that such was the case – (a) reloading promptly would be the standard practice, (b) having a torpedo ready might be useful for self-defense in case of need. It might be that the actual reload would have been deferred for some specific reason such as avoiding an up or down angle while actually moving the torpedo. If it were decided to surface for a gun action, the surfacing could be expected to produce an angle.

    The Hypothesis Report assumes that if GRUNION were surfacing it would be for a gun action. Not addressed was the possibility that it was desired to surface as a last resort in order to cope with flooding. The Kano Maru mentions seeing only the periscope and the “ripples around what looked like the “control tower” but did not report seeing the deck area. For a normal surfacing, and even more for a “battle stations gun action” surfacing, .given their proximity the Kano Maru should have had no trouble seeing the GRUNION deck area. This indicates that GRUNION was heavy from having already experienced at least some amount of flooding by the time it broke the surface..

    Since there were no more shots fired by the Kano Maru after its 84th (the one observed to hit), it is reasonable to assume that GRUNION sank before another shot could be fired, i.e. in less than 32 seconds. (If 84 shots were fired in the 23 minutes between 0547 and 0610, the average firing interval was 16.42 seconds).
    Assuming that Captain Abele ordered, or concurred with, surfacing it can be assumed that he hoped that GRUNION would be able to remain on the surface while the flooding casualty was corrected.and be able to escape. And, thinking ahead, he might even have considered the possibility of using the deck gun, either to finish off Kano Maru or, at least, to facilitate making his escape. To this end he may have alerted the gun crew to standby although it is debatable whether this could have been done concurrently with the efforts being made to cope with the flooding emergency..

    The Hypothesis Report infers that the shell damaged the main engine and/or ships ventilation supply valves. Penetration of the piping aft from these valves would have had the same effect. The Hypothesis Report indicates that this would result in adding 16-20 tons of weight. One way or another I think it highly likely that this piping did flood.

    Elsewhere in The Hypothesis Report this flooding was described as”a significant loss of buoyancy, a problem but probably not a serious one”..
    This compares with the following approximate sea water capacities:
    Conning Tower 24.32 tons
    Safety Tank 23.23 tons
    Negative Tank 7.51 tons
    Bow Buoyancy 31.69 tons
    The Hypothesis Report further states “Subsequent attempts to compensate via safety tank would have failed due to inability to pressurize tank.”. This was due to damage to the Safety Tank Vent port riser from the shell.

    The Hypothesis Report does not mention the debris including pieces of submarine decks and other flotsam seen by the mine layer Ishizaki nor the extensive topside damage which can be seen on the GRUNION photos. Although the Hypothesis Report statement “Okun has stated that the shell likely would not penetrate any great distance into the water” may be correct it appears to me that many of the shells must have traveled far enough to cause considerable impact damage even though slowed enough by the water to prevent their detonation which could have been seen from the Kano Maru and reported..

    The Hypothesis Report infers that GRUNION’s 90 degree starboard turn due to gyro angle considerations was ill-advised. I do not understand the description and logic of this inference but do not think that it is warranted given that both torpedoess #4 and #5 hit as intended. The fact that they did not explode was a torpedo exploder problem, one not recognized as such by the Navy for over a year into the war, and certainly not the result of any GRUNION shortcoming

    David Hardy
    October 3, 2008 | 6:11 pm

    It was well documented (after the problem was finally admitted) that American torps were running lower than their depth setting, and had major problems with the detonator, esp. with the classic broadside shot. Some of the detonators’ components were too fragile, and if hitting at near 90 degrees would break rather than initiate the detonation.

    Of course the Japanese commander would not know this, and when he observes torps passing under his ship, or hitting it without effect, he’d conclude that someone set the depth too low or forgot to activate the detonator. It’d be a natural error.

    David Hardy
    October 5, 2008 | 4:35 am

    Another consideration: what happened to the shell after detonation? I approximate, but a 15-20 lb shell (75-88mm range) with 1.5 lb of explosive, leaves a lot of steel mass there. The hull fragments would have gone sideways, knocking the control room crew out of action (with the force of 4-8 hand grenades) and making the boat unmanageable. But the nose would have continued on, doing whatever damage it did (and at 400 yards, on a flat trajectory, roaming the length of the boat and puncturing many compartments) before possibly inflicting a second puncture in the pressure hull. The effect of such a hit cannot be written off.

    Conversely, I suspect that the effect of a torp warhead detonation would have been more dramatic than is reported and than is evident on the images.

    One must also account for freaks of bad luck. A shell detonation after passing thru water and just before reaching the sail would have resulted in a major water hammer effect breach in the sail, followed by the remainder of the shell doing the above damage.

    The missing fore portion might be explained by the impact of the boat with the ocean floor. After falling a mile through the sea, it could have built up enough velocity to shear the forward area off at first impact.

    John Kiracofe
    October 5, 2008 | 5:31 am

    My apologies in advance if my comment seems to be “condescending” or in any way insulting, as this is certainly not my intention. With regard to the question of where is the Forward Torpedo Room or more simply where is the front part of this vessel, my thought is that if this vessel sank with the front part pointing (more or less) towards the floor of the ocean and the back part pointing (more or less) towards the surface, then perhaps the front part of the vessel is actually embedded in the ocean floor. Could it have actually been impacted into the seabed? And then the seabed held the front portion like a vice and the weight of the back end caused the back of the vessel to shear off at the point where it was sticking out of the surface of the ocean floor? Also could the angle of the bent metal at the remaining front portion of the vessel (in the photos) be somehow used to indicate the angle of the impact upon the ocean floor? Not a hypothesis, just a thought.

    God Bless the souls of those lost in this incident and all who are helping to resolve the issues associated with it.

    David Hardy
    October 25, 2008 | 7:42 pm

    I think Ed Walson’s theory of unintentional broaching beats the alternate of surfacing to engage with the gun.

    Target is known to have several heavy machine guns (13mm is close to our Browning .50) and a cannon, since they were all being fired at the periscope (and the sound of exploding shells would have been audible). Range is about 400 yards, an easy shot for a heavy MG.

    If you surface, the MGs will cut down your gun crew long before they can get to the gun, let alone ready it for firing. Even if they survived, the ship’s gun will get off several shots before they can fire. After that, a vulnerable sub would be trading shots on an equal basis with a ship with the ability to absorb a fair number of hits.

    Surfacing for gun action at that range would be unthinkable. On the other hand, if they broached, commands were issued to dive, and at that moment a shell wipes out the men who could have countermanded it (and at least a 3″ hole left to flood) that might explain things. I’m not sure of the layout of the Gato, but a detonation of that type (probably a 12-14 lb projectile) inside the hull might well have taken out the officers, the helmsman, etc., killed or stunned everyone for quite a distance, wrecked the controls, started fires, etc.

    John Patchen
    November 17, 2008 | 7:54 pm

    As a former Army tank commander and gunner I believe that the likeyhood of the 8cm (actually 76.2mm) gun causing a catastrophic rupture of the hull unlikely. Chances are that the 8cm gun in question was the Mark 3 Naval Gun which was intended as a medium duty anti-aircraft gun. Ballistically speaking I don’t think the odds are even remotely close. Let’s take a look at some of the facts:

    -The Type 3 was a naval AA gun, I’ve researched many guns, but this one seems to be hard to find any data on, however I have never found any indication that they made a Armor Piercing round for this gun as it was designed to shoot aircraft, had it been a DP gun that would be a different story. Based on the data for the gun and the muzzle velocities indicated I think it would be safe to assume that she was firing HE-Frag or HE rounds, both would have proximity fuzes.

    -The 76.2mm guns all had a very flat, shallow trajectory. The Type three had a muzzle velocity of 670m/s or 2200 fps. It fired a 6kg projectile at a direct max range of 7600m, the effective range was 4000m direct fire, 5600 meters in the AA role.

    -The HE-Frag and HE projectiles both had a stated armor penetration ability at 500 yds of between 75-61mm Rolled Homogenous Armor (RHA) at a 90 degree incedence. This value drops to 61-40mm when angle of incedence is 60 degrees.

    -Grunion’s pressure hull was made of high quality steel equilvalent to about 111% integrity of the RHA standard steel of MIL-A-12560. So, until I can find some more solid data on the steel type used on Grunion I will use the properties of MIL-A-12560 for my hypothesis.

    Now here is my hypothesis/arguement against the catastrophic 3″/76.2mm shell hit.

    1) Most witnesses agree that the shell hit the breaking water of at the conning tower. Here is the first and most significant detractor against a catastrophic hit because:

    a. The round would be traveling at a velocity of about 2200fps on a virtually flat trajectory–but fired at a negative angle from the bow AA gun. Assuming that the gun was mounted in pretty much the standard fashion you are looking at a depression angle of -6.5 degrees. Even if the boat was traveling on perfectly calm seas, it is most likely that the round would have had a angle of incedence with the WATER of about 21.5-22.45 degrees. That is assuming ideal circumstances. It is well documented that the seas in the area of the attack are choppy at best. I would hypothesize that the angle of incedence with the water was somewhere around 52-64 degrees.
    Now you are talking about a round striking the water before it strikes the Grunion-we have no idea of how “short” the round was, but based on known ballistic data it is safe to say the the round lost 45-60% of its penetrating capacity right away, and 5-10% per inch traveled in the water. It is highly unlikely that the round reached Grunions hull with the ability to penetrate the hull in scenario. Further more, upon contact with the water the proximity fuse would have been activated. Therefore it is most likely that the round had already begun its detenation cycle outside of Grunion’s hull. Even if the round reached the Grunions hull intact, it only had enough energy to penetrate around 17-20mm of RHA, we know that the steel on Grunion was of higher quality that RHA and was of an approximatel thickness of 5/8-11/16″ or 17.39mm when adjusted for the encreased hardness of the steel, it computes to a corresponding 25-28mm equivalent RHA factor–simply put, the round was out of energy.

    The only possible way for the round to have sank Grunion was if it scored a clean virtually square hit on the conning tower…and most of the witnesses state that the round struck the “wave” or “water” at the base.

    Travis Mullan
    November 26, 2008 | 4:32 pm


    Have you seen this analysis?


    Travis Mullan
    December 1, 2008 | 6:55 pm

    Further to John’s excellent comment above:
    If the original Gato class conning tower design, with the mod to the after end, is reviewed it will be noted that the pressure vessel of the conning tower lies roughly 6+ feet from the top of the conning tower fairwater. This plan also shows that the lower portion, almost half, of the conning tower pressure vessel lies under the main deck superstructure. In the Grunion’s case, with the periscope shears just breaking the surface, it is highly unlikely that a 3″ round would be able to inflict much if any damage to the actual watertight portion of the conning tower. It may be that a round penetrated the fairwater in the periscope or Quartermaster’s area which could explain some of the damage to the light metal of the fairwater.

    Haines Brown
    December 8, 2008 | 3:26 pm

    Terry, for further information and photos of damage to the Irex sail, refer to my site:

    Haines Brown, ET1 (SS)

    January 2, 2009 | 1:46 am

    facinating read might i start off with a lot of theories. might i ask a couple of questions (im not a mariner or engineer) 1) what was the weather like at the time? says foggy but was there roling seas and would this have made a differance to the track of the torpedoes? 2) the ship was running for the harbour -was the attack made as the ship was accelerating if so wouldnt the torpedoes timing be off as its calculted on a fixed speed? 3) the ship mentioned it was avoiding a reef could the sub have struck something while manovering?
    lastly as a wartime area would there have not been minefields nearby and could a possible mine be the culpret. ok some have this might have been covered but these are just thought i would like to add if noone has covered them.
    last is there no sign that in panic or even organised that the crew tried to abandon ship?
    may they rest in peace.

    January 2, 2009 | 2:16 am

    just noticed something else in the photos the hatch covers hve locing bars do they not that are extended when the handle is turned if the haches blew open wouldnt they be visible and bent? from the photos they look like they are retracted which would mean the hatch was manually opened or was open when the sub went down. surfacing to use the deck gun dosnt sound right as they knew they were close to port and the escort may be near.
    noone seems to know if the sub happened upon the ship by chance or had been stalking it if so would it be possible they had run too long without surfacing or extending their snorkel and were low on air. they were engaged in battle previously did they take damage they were unaware of? i believe water on the batteries causes leathal gasses. also knowing they could be possible target for escorts me personally would have had my sonar guy listening hard for their screws surley he would have heard the torpedoe coming if it circled?
    lol sorry guys im just a novice but i like to think outside the box i hope im not sounding to crazy.

    EJ Johnson
    January 2, 2009 | 4:39 am

    I’m not a submariner but want to thank those who served and those who care enough to blog here and help to find answers to this very interesting story. We all come to a better understanding of this grat country with this. God bless and goos luck.

    January 4, 2009 | 6:41 am

    the circle runner is a very big Possibility…It happened to the USS Tang and is suspected in the sinking of other fleet boats….If the USS could be photographed, we could compare the damage from her torpedo strike with the possible possible torpedo damage on the grunion.

    Travis Mullan
    January 5, 2009 | 8:16 pm

    See link below for picture of a torpedo test on a deactivated fleet sub:

    G Wilson
    April 20, 2009 | 5:47 am

    I have studied the images on this site and read through most of the comments on the condition of Grunion as she lies on the bottom. The images, drawings, plans and research are extraordinarily well done. In my opinion the catastrophic damage to the bottom half of Grunion’s hull is most probably due to heavy impact with the bottom after falling 500 fathoms while full of water. Topside damage could have been the result of rolling over and sliding down the slope- although my first thought was that she had been run over by a surface ship.

    Images most certainly show a large impact explosion- of whatever cause- which started Grunion on her last dive. The huge amount of damage topside was caused by that set of impacts as shown in the images and exhaustively discussed.

    Regarding the conning tower hatch- bent into a “U” shape and the missing bow, I offer another possible explanation: Explosive combustion (dieseling) inside the hull caused by extremely rapid compression of air in the hull mixed with oil (hydraulic, fuel oil, lube oil…) as water enters the compartment quickly.

    When a sub goes down it retains air in each compartment if it is intact . As the water rushes in at at phenomenal rate, the hydrocarbons and air in the compartment compress and explode. The resultant explosions blow out each bulkhead one by one as the sub sinks. In the bow torpedo room the explosion might either blow the bow off by itself or trigger secondary explosions (torpedo warheads principally) which blow the bowcap (the rounded end of the pressure hull) off the submarine. This phenomenon could also be the cause of the conning tower hatch damage and probably the battery hatch (it appears the dogs on the hatch have been torn off leaving the hatch looking normal in its locked up position.)

    The bow of the I-52 has a similar missing portion-bowcap and outer hull- probably due to a dieseling explosion in the forward torpedo compartment.

    Matt Turner
    March 30, 2010 | 2:04 am

    i do have a question? what was the final moments of the Uss grunion i mean it sounds like she was deph charged more then a couple times for this much damage to the sub and also did anyone on the dives find the torpedo hatches open?

    Travis Mullan
    October 8, 2010 | 7:03 pm

    I have been reviewing the photographs, CDs and discussion for the umteenth time in an attempt to come up with a reasonable explanation for the missing bow section and the battery room, control room failure to implode. Beginning with the midship area I would like to propose the following:
    In re-examining the conning tower hatch and surrounding area I have found it reasonable that the damage to the area may not have been due to physical contact, with the sea bottom for instance, but due to the beginnings of implosion. The conning tower pressure hull is supported at its forward end by the vertical bulkhead which does not appear to have much distortion. The next supporting structure, with the exception of the strengthening rings, is in the area of the periscope shears. Located between the periscopes and the forward bulkhead is the access hatch to the bridge which is located forward on the starboard side. Looking at this area on the Grunion photos there is a great deal of downward distortion of the upper conning tower pressure hull mainly in the center. This distortion has caused the periscopes to be drawn forward and down. In looking at the hatch it can be seen that the hatch trunk has been drawn downward on the port side as the conning tower distorted downward. This progressed until the hatch separated from the hatch trunk alowing water ingress to the hull. Once the separation occurred the inflow of water stopped further distortion of the conning tower.
    As the sea water entered through the distorted hatch it ran into the conningtower and then down into the control room and pooled against the forward bulkhead and in the pump room below. The inflow of water began to compress the air within the sealed control room and after battery heating it as the pressure increased. If the battery had been spilling acid due to the extreme down bubble the acid would mix with the sea water and generate gas. As the air temperature continued to increase a flash fire would have swept these compartments and possibly touched off a battery explosion. If the explosion were of sufficient force it could account for the open hatch behind the conning tower fairwater.
    I hope that this will generate some thought about this area and possibly some other ideas as to what happened here.

    Regarding the 25 feet of missing bow area:

    Several Gato and Balao boats experienced uncontrolled dives before, during and after WWII. Those that survived these traumatic occurrences have documented the cases well. The reasons range from jammed hydroplanes to errors in ballast and boyancy tank control. For whatever reason, if the Grunion found herself in a similar situation she would probably have been traveling forward with an increasing bow down attitude. Blowing ballast first and then reversing the motors have been documented as successful in some of the survivor cases. In the case of the Grunion let’s say that they were unable to recover in time. With the bow being the lowest point on the boat it would be subjected to the greatest amount of sea pressure and would be the first compartment to implode. The loss of boyancy and increased weight at the bow would increase the forces already working to sink the boat.
    In reviewing the photos and video of the wreck it is clear that the colapsed compartments did so from the overhead in a downward direction. This may be due to the structural strength provided by the internal decks. The bulkheads seem to have withstood the forces well and maintained their shape. The forward area of the forward battery room overhead looks quite similar to the torpedo room overhead area on the other side of the bulkhead. Let’s say that the torpedo room colapsed from the overhead downward which would deform the metal downwards and inwards resulting in the beginnings of the deformation observed on the wreck as she was found. As the boat continued toward the sea floor the forward battery would have been the next compartment to colapse. This would result in additional loss of boyancy and encreased weight on the forward end of the sub. Finally with no boyancy remaining the Grunion would have impacted the sea bed with considerable velocity. We know that she struck bottom on the slope of a sea mount which would have resulted in an impact at an angle of somewhat less than 90 degrees. Picture the forward torpedo room with the overhead colapsed to the deck level, as in evidence in the case of the other compartments, and with a raised area to the torpedo room/battery room bulkhead. The forward area of the bow may very well have imbedded itself in the sea bottom and sheared off in front of the forward ballast tank, the pit area. If the bow was bent downward and was overrun by the sub what remained of the bow may bave impacted the bottom a second time before the stern settled and she slid the remainder of the way to the bottom. This would account for the way the hull is deformed at the bow as she sits on the bottom now.

    Please share your thoughts and ideas.

    Mark Westmoreland
    May 20, 2013 | 4:34 pm

    I try to put myself in the shoes of the captain. Without personal knowledge of his demeanor I could only say what I might have done. There could have been a calamity of errors here not simply one lone reasoning for the sinking.

    If I had just fired off all those worthless fish, and as some captains knew of their unreliability, I may have become emotional compromised in my anger towards their makers and those who ordered their use. Fish that have not only ran deeper than they were expected but now the damn things have hit the target and broke like some child’s play toy.

    I’m not a very happy man at the moment. My fastest action in taking the enemy ship out is now the only reliable item I have, my deck gun. Knowing that the enemy ship has surface weapons I wish to put distance, speed and my gun to use. All ahead Flank, blow main ballast, order the gun crew to stations, Left full rudder. The cavitation begins to create a wake of bubbles seen from the enemy ship but I want my gun on her as quick as possible. As the boat rises a lucky shot from the enemies gun passes under water then back up ripping a hole in the submarine causing the buckling of steel and hatch in the conning tower. There is a high pressure surge of water entering the submarine causing the air to compress and perhaps blowing outwards the already loosened mess hatch.

    I might have order a dive in hopes of repairing the damage and getting farther away to resurface and use the deck gun but the damage is more severe and with the opened hatch the submarine floods quickly and sinks. If the boat had rolled over and struck the sea bed bow first upside down it is possible for it to have rolled over while settling on the bottom at the angle it hit causing the metal to have been bent downwards as some post indicate.

    It is also possible that a circling torpedo could have been to blame for the bubbles seen on the surface and while the submarine begin to rise the malfunction fish hit the bow or the conning tower but did not detonate and only began to cause flooding while the errant shell from the surface vessel struck the conning tower and then the mess hatch flew up under pressure giving three point of flooding not simply one or two. The bow damage could still then have been caused by striking the sea bottom.

    The, “Big black-brown water arose”, could have been a mixture of leaking fuel mixed with cavitated water as the submarine angled downwards at flank speed or as the submarine dove because of a failure in equipment which had been reported on other submarines with uncontrollable dives.

    I would love to find more links to any video or photos of the grunion after the ROV dives.

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