Sonar Image Analysis


As a result of the recent Associated Press article there have been a number of responses expressing doubt that the sonar image represented the Grunion. I would like to present the facts behind our optimism.

This is not an attempt to persuade the doubters.

Instead the goal is to present the whole story so that skeptics can provide a balanced and intelligent analysis. We would very much appreciate such responses. Moving forward on false assumptions is not going to be helpful to anybody.

There are several points:

To start with sonar images can’t be read like photographic images. If you go to you will see a set of 3d images viewed (either light or sound pings) from different directions. In addition note that it makes a difference whether the sub is tipped to the side (possible 5 degree port list with 7 degree down pitch) and or whether you are looking at it perpendicularly. In most cases we weren’t. There is enough bandwidth in a photographic image to determine these factors; with a sonar image that is not the case. It is dangerous to make a judgment solely on the sonar image. The one shown in the AP article was particularly misleading. Below are a couple that are better



The length of the image (285 ft) is consistent with that of a Gato class sub The sub is actually 312. The bow appears to have been buried or blown off which would explain the missing 27 ft. (Two of the images appear to show a buried bow section) A destroyer is 375 ft and it appears that we have located the only destroyer sunk in that area, the Japanese destroyer Arare almost exactly where predicted and several miles away. Sub chasers are 165 ft and although two were sunk they, along with the Arare, were a number of miles distant from the sub target. The Japanese sub I-9 which is 375 ft was sunk west of Kiska far from the target. That combination of location and size rule it out also. On the other hand the National Park Service found a sub in Kiska Harbor 243 ft long in 80 feet of water. Measuring length of a sonar image is a function of speed of the towfish which is measure by GPS at the surface. Just how accurate and reliable is that speed unknown.

The sub appears to have slid about 1200 meters down a slope which because of the topography and the fact that the volcano on Kiska has had at least two major eruptions since 1942, may be volcanic ash. There is a reasonable possibility that some of this volcanic ash or silt has built up on the sub distorting the image.

Prop guards: When enhanced one of the sonar images shows what appears to be a prop guard, a rectangular protuberance that protects the propellers when docking and also protects against mines.

Some navy personnel believed that prop guards were removed when a sub went into action. However, according to John Alden “ I believe it can be positively stated that she did. [have prop guards] A photo taken 20 March 1942 clearly shows them and the directive to remove the guards for existing and new subs was issued on 1 September 1942. GRUNION was lost before that [July 30, 1942] and had never been modified from her initial configuration.”

The presence of prop guards would seem to eliminate the hypothesis that the target was a surface ship. However, the images do not indicate with absolute certainty the presence of prop guards. See the photos below.

Prop guard (full size image)

Prop Guard annotated

Finally we did a great of work on determining the location and ended up with some fairly definitive coordinates. The sub was almost exactly where we expected.

All of these points seem consistent with the hypothesis that it is the Grunion. As yet, we have not seen any points that are clearly inconsistent with that hypothesis.

Again, we would appreciate learning of inconsistencies with the Grunion hypothesis.

22 Comments for 'The Sonar Image Analysis'

    Greg Crane
    October 19, 2006 | 1:35 pm

    Outstanding site! Just a quick thought concerning the apparent discrepancy in vessel length: a shortening in the apparent size of the boat could be due to a hydrostatic collapse at either bow or stern of the vessel. USS Scorpion suffered the same kind longitudinal compression during her foundering. It’s a bit difficult to tell from the sonar images you have, but there does seem to be a distinct reduction in hull circumference towards the top end of the image which might back this hypothesis up…..

    Garry Kozak
    October 22, 2006 | 1:18 am

    I have reviewed the new images in the Sonar Analysis link and my conclusion is still the same as earlier, this DOES NOT look like a sub. I have imaged several subs over the years and your images have none of the characteristics of a sub. If you would like a better analysis of your target provide image with no water column removal/slant range correction and the range scale the data was collected on (scale lines are preferred). I also believe your mensuration of the wreck may be in error.

    December 20, 2006 | 10:18 pm

    Possible that the bow is buried or completely off though. We’ll find out for sure soon hopefully whatever the wreck is.

    April 12, 2007 | 11:50 am

    I think you are on the right track. I have wondered about mystery of The Grunion for 30 years. Wish I could be there.

    Rhonda Raye
    April 17, 2007 | 6:10 am

    If you have been wondering about the Grunion for 30 years, would you happen to be a relation of one of the crewmen?

    Yutaka Iwasaki
    May 24, 2007 | 1:48 pm

    Title: ‘Behold ye despisers, and wonder, and perish. ‘

    I draw ARARE possible view. It is from the sonar image that obatined last summer.
    Almost canal of Mars. :-) The grids are 5m square.

    Destroyer ARARE
    Sunk by USS Growler SS215, Lcdr. Howard W. Gilmore, on Jul. 5, 1942.
    Gilmore was KIA on Feb. 7, 1943 at Solomon. The last word was ‘Take her down’.
    Growler was lost on Dec. 8, 1944 during her wolf pack attacking oiler BAN-EI MARU.

    May 28, 2007 | 2:15 am

    Yutaka’s drawings are featured in a new post on the blog. Please see them there…霰-ijn-arare-hail-15-april-1939-5-july-1942-キスカ-kiska-alaska/

    Alice F. Steen
    December 11, 2007 | 2:11 am

    I had never heard of the USS Grunion, until I read an article in the Readers Digest. I made a lot of reports in school about WWII and never heard of it.
    I had a lot of curiousity about WWII, since I was born on Pearl Harbor Day. I have more information to give to my Grandson, He is also into WWII History because of me.
    Thanks for your memories.

    Nigel Hampson
    December 19, 2007 | 1:07 pm

    Hi everyone,
    Im new to this mystery. I’m shortly taking delivery of a large model sub kit (6feet long) of a Gato class boat, and would like to make it as the Grunion. Could anyone advise on a source of Pictures etc to help me modify the basic model kit?
    Is there any fresh new re the wreck sonar images?
    im no VERY intrigued.

    Yours etc Nigel Hampson, Burnley, England

    Nigel Hampson
    December 19, 2007 | 1:08 pm

    im no VERY intrigued

    SHOULD read im NOW VERY intrigued ! Sorry.

    Meryl Kretschmann
    December 21, 2007 | 5:20 am

    “Families never stopped searching”
    The Readers Digest Article , January Issue, has put the icing on the cake.
    The pictures of the Abele family , the Aquila and crew are super !!
    There was a picture of the Grunion and some undersea shots.
    The story was very well written and tied together the continuing events.
    I got the first comment today from a friend and he immediately faxed me saying the story was “fascinating and that it affords some closure for the families by resolving all doubts”
    That is true- this is our Christmas Miracle
    Meryl Kretschmann (father Carson Martin)

    David Fortin
    March 11, 2008 | 1:35 am

    I was doing reserch to build an early Gato from the Trumpeter kit and found this sight. I was touched deeply by the photos and historys that I read here.
    As an ex-submariner I have an intrest in all thing submarine and have done much reading on the subject. I’m convinced a circular run killed the Grunion.
    I’ll be building my submarine kit as the USS Grunion and would like to share some pics of the compleated model upon compleation.
    Thank you

    Steve Giles
    April 26, 2008 | 9:47 am

    Hello ~ just wanted to ‘chime in’ with a personal note; I have been diving on sunken submarines… one of note the old 1918 S-37, which torpedoed and sunk the first Japanese Destroyer (NATSUHIO = “Summer Current”) and having DIVED on sunken subs… a ‘sonar-photo’ cannot give MANY details… ONE writer said ”sub bow could have” , and I’ll use my term; ”TELESCOPE” under pressure, is completely correct. It also could be partially buried, as many of the shipwrecks I have visited usually are, whatever end hits soft bottom first.
    When I was DIVING on a submarine, it was not always easy to see details, as they were overgrown or damaged in one way or another. Going INSIDE was the REAL test, then you could find items with visible markings such as ”Periscope Fuse Box”…… ”diving alarm button” (WITH watertight rubber finger button cover!!!) Leave the experts to do their job… they are the ones who do the job so we can read about it in our ‘armchairs”… salute to all Vets… esp. Sub Vets.. either here or ‘on eternal patrol’… thanks.

    August 3, 2008 | 1:51 am

    aaa auto insurance michigan…

    frisks Mathematik,migrating …

    Milo Hyde
    October 4, 2008 | 10:17 pm

    Congratulaitons to the Abele brothers and the members of the search expedition. You have done a great service for the families of the crew memberrs and made an invaluable addition to our Navy’s history.

    Milo Hyde
    USN (ret)

    January 1, 2009 | 6:45 pm

    Hi, I saw a comment regarding the original translation possably not giving a correct interpretation of the original Japanese. I currently live in Japan ( I’m British) and having done my time in the service as did my father and grandfather would like to make the offer of having the original Japanese looked at by some professional translaters I know here in Japan. If it would help, I could have the original text looked at by a few people to give you perhaps a better understanding on what was written by witness’s.I also have a working understanding of Japanese so could help them to correctly translate any terminology.Oh, also I’m pretty sure I can get this done at no cost, depending on the amount of original text you have.Some of the people who would look at this are ex navy and merchant seamen who now teach at a college preparing students for a career in coast guard and merchant navys, so they have the background to recognise what they are reading and make some sense of it in English. The offer is there if you want to take it up, please contact me.

    Lisa Mills
    January 2, 2009 | 2:30 am

    I truly appreciate what these two men have done. Its interesting to note the cost was not disclosed, as the tax payers did not foot this bill. It was, however, a naval vessel.

    From one American: Thanks for your hard work.

    Mary D. Allen
    January 2, 2009 | 3:27 am

    How wonderfull this must be for you Brothers. I was A little girl when “The World War” started,and even I felt the pain that loved ones felt at the lose of Dads,Brothers, And uncles and Sweethearts. The world is better because of people like you. Mary allen

    Diane N.
    January 2, 2009 | 4:18 am

    This is very interesting – I would love to see a TV special on this. Good job!

    January 2, 2009 | 7:26 am

    as a marrineer a major history buff i want to say hoorah for your efforts. this is an extraordinary accomplishment and exiting moment for all marriners coodos gentalmen cooddos.

    Ed McDowell
    March 19, 2012 | 4:28 pm

    I read somewhwere that propeller guards were removed from the wartime boats to reduce noise vibrations and things that could be snagged by hooks. Might have read it in one of Dick O’Kane’s books.

    Bob Sminkey
    November 30, 2014 | 4:33 am

    I noticed that a couple of photos of the “open hatch” showed the portable hatch grab rail installed. Why would the hatch grab rail be installed if the Grunion was rigged for sea? If I am not mistaken, the portable hatch grab rail was stowed inside the trunk. Is it possible that the Grunion surfaced or broached at some point during the battle? Maybe this would explain the open hatch and the installation of the grab rail. The photos of the open hatch show the hatch dogs but I can’t tell if they are damaged or not. I noticed that one of the photos of the Grunion in upkeep with the hatch open did not show the grab rail installed. Great site and a real tribute to the brave men that were lost. Keep up the great work.

    Bob Sminkey

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