Re: IJN and sound velocity profile


"Jack Linthicum" <jacklinthicum@xxxxxxxxxxxxx> a écrit dans le message de
news: 1146308816.682750.138950@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

(snip)

Redacted to remove excess, Japan seems to have been interested in
ultrasound for flaw detection but seems to have also dropped all
research for WWII. The basic idea seems to have been an outgrowth of
radar and used water as the transmission medium. You need lots of
researchers, each starting from one basic observation, to need to reach
out into other applications. The thermocline phenomena probably was
found empiraclly but some Japanese submarine commanders but the
"attack" doctrine of the Japanese submarine force may have precluded
sharing the knowledge officially.

---- (common answer to all contributors)

In fact, IJN did have two types of active sonar device on some of its DD and
CL:
- Type 93 Sound detection apparatus
- Type 93 mod 1 Sound detection apparatus

The first one was approved in 1933 as indicated by its name but was
apparently not installed on DD until 1935. Extensively tested (at least)
during naval maneuvers in 1938, it did not seem to give full satisfaction.
Some reasons for this disappointment might have been the technical shortages
of this device (range 4000 yd at best against a target under 90 degrees,
bearing discrimination 5 to 3 degrees - that was no that bad for the time),
by the fact that IJN task forces usually transited at speeds which were
incompatible with ASW listening (14kts or over in transit, 18kts at
economical speed in operations), or by the bathythermic conditions in
central Pacific, with a sharp negative temperature gradient in the first 20
or 40 meters.
Tested again during anti-submarine maneuvers in homeland waters in 1940,
Type 93 did nothing to prevent IJN subs from perpetrating a virtual carnage
among the commercial ships.

Type 93 mod 1 was an improvment of the previous, with increased range and
much better angular discrimination. It had been developed with German
assistance. It was first installed in Yugumo class DD, the first units of
which were just rolling out of the docks at the time of Pearl Harbor. It
became the standard active detection device throughout the war, despite its
installation was not generalized on escorts (smaller than DD, I mean
Kaibokan, moderinzed 2nd-line DD and patrol boats) until 1943. Mass
production had been ordered at the beginning of 1943 AFAIK, but the device
suffered quality problems for several months until its industrialization and
testing process were improved. Japanese officers themselves did not consider
that it had reached maturity until the summer of 1944.
Then the Japanese experienced bitter disappointment when they discovered
that this promizing device had what they called a "random functionning", and
in late 1944 US submariners noted that the Japanese seemed to ignore the
effects of layers.

Thus my question. I know that there was no computers on ships at this time,
that neither Sound Velocity Profiles nor Temperature Profiles were exploited
to model acoustic propagation and to predict ranges. But a rough correlation
(at least) between seawater temperature and noise level heard from SONAR had
obviously been made by IJN submarine captains (and by German ones too), and
was exploited in escape maneuvers.
USN did install a BT box from 1944 onwards on its subs to record temperature
on paper, and that's apparently all they did aboard operational subs during
the war. I just wonder if Japanese ASW teams aboard surface vessels took
benefit from what had been found by their submariners.

Japan also had a passive set, known as Type 0 sound detection device, that
had been discussed several months ago on this newsgroup. It was installed on
all surface units from 1940 onwards, including the Yamato and Zuikaku
classes (and subs, of course). On surface warships it was found to become
deaf at speeds over 6 to 10kts except on "high" frequencies (high for the
time), according to the mother ship, and was therefore considered usable
just during channel entrance and clearance maneuvers, or as a
torpedo-warning device, not as a fully operationnal anti-submarine detection
device.

Regards,
Christophe Chazot

(snip)


.

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