Re: IJN and sound velocity profile


"Jack Linthicum" <jacklinthicum@xxxxxxxxxxxxx> a écrit dans le message de
news: 1146236647.927647.292980@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Christophe Chazot wrote:
Hello, this is a serious question.
I'm looking for information about possible exploitation of sound velocity
profile (SVP) or bathythermography (BT) by the Japanese during WW2.
As far as I know, no IJN surface warship had any device to measure SVP or
BT, and convoy escorts simply ignored sound propagation conditions when
they
tried and establish a screen around a convoy, leading to irrelevant
position
of sonar-equiped ships. On the other hand, IJN submarines did exploit
temperature gradients to escape from detection, in 1944-45 at least but
maybe earlier. So what ? Did they never exchange their experiences, or
did
they but lacked time / means to inforce relevant tactics in surface
forces?
Has anyone some relevant info ?

Regards,
Christophe Chazot

The Japanese Submarine Force and World War II says the I-400s and
I-13/I-14 had anechoic coating, suggesting the idea was there.

You have clear photographs of this coating on pages 92 - 93 of "I-400,
Japan's secret aircraft-carrying strike submarines" and a short explanation,
but this coating gives no indication that the Japanese knew how SVP or BT
layers had an impact on sound propagation through water.

Later quote "The IJN had very little concern for the protection of
Japanese shipping lanes or ASW tactics and operations. There was no
Japanese navy policy for countering enemy ASW....their lack of fully
modern electronic sensors, slow submerged speed, shallow maximum test
depth and bad manuerverability...made them easy targets for astute ASW
forces"

In December 1942 or January 1943 (my sources are not very clear), the 12th
department of the Naval HQ issued a "doctrine related to the protection of
communication lanes of the great east Asia", which was the first "ASW
policy" of IJN. It was pretty irrelevant at this time but was improved
several times. In October 1944 it had become more consistent, recommending
close cooperation between aircraft and escorts and with search patterns for
MAD-equiped and radar-equiped planes, but rather strangely it does not
mention anything about sound velocity profiles or anything close that could
have helped omptimizing sonar operation or escorts positioning around
convoys. That's why I suspect they hardly had an idea of it. Other clues are
that I've never heard or read anything about a dedicated bathythermograph,
that none of the numerous requisitionned crafts acted as ocean survey ship,
and that US subs frequently noticed that IJN escorts seemed to have no idea
of the role of temperature layers, as far as they could judge from the
reactions of escorts.
But I do not understand how IJN sub captains (or, at least, some of them)
knew that they could hide under layers. Did they learn it from their German
counterparts ? and why didn't they inform the 12 dept.?

BTW, thanks for your answer and cooperation.
Regards,
Christophe Chazot


.

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