Hi,

I will be using term "hydrophones" for passive listening equipment and "sonar" for active listening equipment.

Generally, during the war, Germans U-Boats were fitted with hydrophones, so called GHG (Gruppenhorchgerät). It consisted of set of sound receivers, fixed to the bottom part of the U-Boat bow. The signals from the receivers were transmitted to the set of delay lines in the phase compensator. By turning the hand-wheel, the delay lines were so adjusted with receivers to receive the loudest signal.

It was sonic device.

The range of this version was up to 20 km to individual ships and up to 100 km against convoys. Accuracy less than 1 degree.

The GHG was later improved to so called Balkon-gerät.

For a short time Germans fitted U-Boats with so called KDB (Kristall-Dreh-Basis), the set of receivers installed on the trainable head on the upper deck, at the bow of the U-Boat. You can see it on the Buchheim's photos of U 96.
It was quickly abandoned due to vulnerability to damages from depth-charges.

Germans also developed the active equipment. One of the reason for modifying type VIIB U-Boat into VIIC version was a requirement of the greater space in control room, to accommodate new sound equipment. The active equipment was designated as S-gerät. There were few versions: with trainable head with transmitters/receivers retractable from the keel (manually or electrically driven), or with set of transmitters/receivers fixed to the stem of the U-Boat

This latter version was used for searching and avoiding naval anchor mines.

Some of the U-Boats were fitted with S-gerät, however commanders did not use it frequently due to fear of betray own position. It was general problem of German commanders, because they relied on the passive observation: visual as well as acoustic. When U-Boats were fitted with Radars (Germ. FuMO), they do the same: did not use them, relying on enemy radar receivers (Germ. FuMB ).

So unused active acoustic equipment was removed and not installed on newly built U-Boats.


US submarines were fitted at the beginning with ultra-sonic, sharp-beam hydrophones in the form of receivers installed at the trainable T-shaped support, at the upper deck. It was called JK, and similarly as German KDB, it was vulnerable to depth-charges. It has listening range up to 5 miles and accuracy up to few degrees. Quickly it was modified by adding transducer, to provide echo-ranging feature.

Americans did not make passive-array (i.e. fixed) listening equipment that time, because they did not solve the difficult problem of phasing elements.

When Allies captured U 570 in the summer of 1941, they discovered the GHG device. US Navy stated that they did not have similarly effective sonic device (until 1944, when they introduced sonic equipment type JP, by this time however, Germans had considerably improved their own passive listening arrays).

After war, when Americans evaluated U 3008 (type XXI U-Boat) fitted with Balkon-gerät, they installed the passive acoustic array in the USS Cochino. After trials, they copied German device as BQR-2 sonar, and then as BQR-4 (enlarged version) and installed it in the their GUPPY and other SSK submarines.


So summarizing, Germans had developed hydrophones (sonic GHG) as well as sonars (super-sonic S-gerät), but in general usage were only hydrophones.

Americans had developed hydrophones (passive part of super-sonic JK device and sonic JP equipment) as well as sonar (JK equipment).

The main difference is that initially Americans used super-sonic listening, while Germans: sonic. And Germans used fixed arrays (due to solved problems of phase compensation), while Americans had to use trainable heads with receivers.


There was also a German device called "Nibelungengerät": sonar, intended for usage with type XXI U-Boat torpedo fire control system, to conduct blind (without periscope) torpedo attacks with Lut pattern running torpedoes. Because type XXI U-Boat was not used in combat, I skipped the further description.

--
Regards
Maciek


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