IJN above-surface torpedo doctrine

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Dod Grile
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IJN above-surface torpedo doctrine

Postby Dod Grile » Wed May 21, 2014 12:22 am

Does anyone know whether the Imperial Navy's surface torpedo doctrine preferred curved fire ahead (with increased gyro settings) or straight broadside fire during WWII? I know USN destroyer skippers much preferred the former...but I haven't seen much documentation from the Japanese side.

Byron Angel
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Re: IJN above-surface torpedo doctrine

Postby Byron Angel » Wed May 21, 2014 2:22 am

Dod Grile wrote:Does anyone know whether the Imperial Navy's surface torpedo doctrine preferred curved fire ahead (with increased gyro settings) or straight broadside fire during WWII? I know USN destroyer skippers much preferred the former...but I haven't seen much documentation from the Japanese side.


..... I have IJN DD torpedo launch data for about 15 surface torpedo attacks undertaken during the Solomons campaign between April and November 1943. All were executed with torpedo tubes pointed more or less abeam and executed (with one exception) using a zero degree gyro setting; the sole use of a gyro setting other than zero degrees (port 30deg) was remarked as having been made necessary by a jammed torpedo mount.

As for US DD practice, I do not believe that curved ahead fire was really at all practiced in WW2. The curved ahead fire notion as part of a massed flotilla torpedo attack was, I believe, an inter-war scheme borne out of anticipation of a large "Plan Orange" type of battle-line engagement. Examination of track charts of US destroyer torpedo attacks in the Solomons campaign suggests short range abeam fire with the launching ship on a reciprocal parallel course with respect to the target. Modest gyro settings (1-2 deg) may have employed from time to time to create a spread pattern, but my suspicion is that in actual combat spreads were most commonly produced by a successive launch of individual torpedoes in a timed sequence.
FWIW

B

Dod Grile
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Re: IJN above-surface torpedo doctrine

Postby Dod Grile » Wed May 21, 2014 3:14 am

Hello,

Thanks for that; I am glad to learn this. And it makes some sense. (How the torpedoes were fired with the tubes pointed "more or less abeam" is a mystery & bit hard to accept, though. I'd like to know more about that, certainly. Does this mean the ship had to orient itself to provide the Sight Angle when firing?)

You're probably quite right about USN practice, though. I meant (& should have specified) that I was thinking of the confusion caused in some early actions in which various American DesDivs did not have the same tactical doctrine...This was certainly a holdover from inadequate pre-war training. A real mess in some instances resulted when some division Cdrs wanted curved ahead fire and others straight broadside...

As for the Japanese information---that's also very good to know. If I could have another fifty years on this earth, I might attempt to sort out Tassafaronga thoroughly, but no chance realistically.

DG

Byron Angel
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Joined: Sun Mar 06, 2011 1:06 am

Re: IJN above-surface torpedo doctrine

Postby Byron Angel » Wed May 21, 2014 11:38 am

Dod Grile wrote:Hello,

Thanks for that; I am glad to learn this. And it makes some sense. (How the torpedoes were fired with the tubes pointed "more or less abeam" is a mystery & bit hard to accept, though. I'd like to know more about that, certainly. Does this mean the ship had to orient itself to provide the Sight Angle when firing?)

You're probably quite right about USN practice, though. I meant (& should have specified) that I was thinking of the confusion caused in some early actions in which various American DesDivs did not have the same tactical doctrine...This was certainly a holdover from inadequate pre-war training. A real mess in some instances resulted when some division Cdrs wanted curved ahead fire and others straight broadside...

As for the Japanese information---that's also very good to know. If I could have another fifty years on this earth, I might attempt to sort out Tassafaronga thoroughly, but no chance realistically.

DG



..... Tassafaronga is a fascinating battle (I am quite interested in the Solomons night actions). Have you seen Russell Crenshaw's book, "The Battle of Tassafaronga"? I thought he did a very good job sorting out the confusion. Kilpatrick's "Naval Night Battles in the Solomons" is another very good book, although it covers all the Solomons engagements.

Re broadside fire of the torpedoes, I am by no means a "hands on" torpedo expert, but from my studies, it comes down to the nature and mechanics of developing the torpedo firing solution. Reduced to its basics, this is essentially a simple geometry/trigonometry problem involving angles and relative speeds (target versus torpedo). The essential components are (a) target speed and (b) target inclination relative to firing ship. Once these are known the firing solution (i.e. - lead angle) for any given torpedo speed setting can easily be computed. The lead angle is basically applied by putting the torpedo mount on a suitable bearing relative to own ship heading, making sure that the selected bearing lies within thearc of fire of the torpedo mount itself (assuming no use of gyro offset). The arc of fire of a centerline torpedo mount was never more than +/-45deg of directly abeam. One interesting feature is that the solution is "technically" range independent - the only consideration is whether the interception point is within the running range of the torpedo. The process is, of course, rather more complicated. since the torpedo officer is usually setting up his firing solution for some future moment, then waiting for the target to reach the desired target bearing before launching the torpedoes.

FWIW

B

Dod Grile
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Posts: 23
Joined: Wed Feb 12, 2014 4:31 am

Re: IJN above-surface torpedo doctrine

Postby Dod Grile » Wed May 21, 2014 7:38 pm

Hello B,

Thx again. I see what you are telling me and that makes sense...but, I wanted to be sure that we understood that the mount MUST move some for the proper sight angles needed. What you wrote confirms this.

"The lead angle is basically applied by putting the torpedo mount on a suitable bearing relative to own ship heading, making sure that the selected bearing lies within the arc of fire of the torpedo mount itself (assuming no use of gyro offset). The arc of fire of a center-line torpedo mount was never more than +/-45 deg of directly abeam."

It might be worth knowing that early (interwar) DD doctrine preferred firing their torpedoes as far astern as feasible. This apparently had a beneficial effect on how well they ran...and I do not doubt it.

Some basic grasp of the trigonometry involved is indeed very useful in understanding how above-surface torpedo attacks unfolded & developed during the PacWar, certainly.

And yes, I've looked at the R. Crenshaw Tassafaronga book you mentioned. What is fascinating to me is that the official IJN charts of the action--in their primary source documents--make no attempt at all to show the torpedo tracks...and I have to think this is due to the confused and complex nature of the action that night.

DG


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