The boat has three passive listening devices.
One on the top of the deck ... that is the JP sonic passive hydrophone. JP is the Navy term for sonic listening gear. The J means that it can be used for listening only. The second letter P merely indicates the model.
Sonic gear is useful for picking up targets at great distances because sonic sounds travel farther. Also, on the JP gear sounds appear more natural and are more easily recognized. Therefore, you can identify not only the machinery noises of enemy ships, but also any telltale noises your own submarine is making.
There are two supersonic hydrophones under the boat in shafts that make them retractable.
Supersonic gear picks up sounds too high for the human ear to hear and changes them into sounds which can be heard.
JK/QC is the Navy term for one type of supersonic gear. The JK half of the combination projector is for listening only; the QC half can also be used for sending out sounds into the water.
QB designates the other type. As indicated by the letter Q, the QB projector can send as well as receive sounds.
Supersonic gear is useful for picking up the important supersonic noises that sonic cannot get. Supersonic gear is especially superior for catching the bursts of supersonic sound used by enemy escort vessels in searching for our submarines. (In addition, QB and QC gear can be used to send out sounds into the water to determine the range of an enemy ship.)
It consists of three main divisions: QB, JK/QC, and NM. The QB projector is a spherical hydrophone mounted on the lower end of the starboard training shaft. One face contains rochelle salt crystals, which change shape when a sound wave strikes this face of the projector. The other side is empty.
The JK/QC combination projector is mounted portside. The JK face is just like QB. The QC face contains small nickel tubes, which change size when a sound wave strikes this face. The NM Projector looks some thing like a small steel coffin. It is bolted flush with the bottom of the submarine in the forward trim tank. The NM projector gets the current needed to send out pings from the same driver that is used with the. QC system.
When a submarine is running submerged, normally two men are on sonar watch. One is on the JP in the forward torpedo room. The other is at the WCA stack in the conning tower. The conning officer is at the periscope.
from:
NavPers 16167
Produced for ComSubLant by Standards and Curriculum Division Training, Bureau of Naval Personnel. Submarine Sonar Operator's Manual
June 1944
CONFIDENTIAL
===============
Chapter 5, page 38
"When your submarine surfaces, you will continue searching. While it is running at a slow speed, you will be able to listen efficiently."
http://www.hnsa.org/doc/fleetsub/sonar/index.htm
In the book, U.S. Submarines Through 1945: An Illustrated Design History, By Norman Friedman, page 198 states:
"Only in 1940-1941 did the U.S. Navy encounter British thin-steel domes, which made it possible to operate at about 15 kts."
This made it possible to use passive sonar to 15 kts.
By 1945 a single capital or merchant could be detected at 10,000 yards, a convoy at 15,000 and escorted capital ships at 20,000 yards.
This makes the idea of mods reducing passive sonar levels unrealistic.
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Generic Mod Enabler - v2.6.0.157
RFB_2.0
RFB_2.0_Patch_23April2010
RSRDC_RFB_V575
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