Surface Ships defences
Within two weeks of the first Accoustic Torpedo (Gnat) attack, counter measures became available. It was code named "Foxer," and was a noise maker towed astern of an Escort to attract and then detonate the homing Torpedo. However "Foxer" could not adequately be used above speeds of 15 knots, and it did interfere with "Asdic," operations. The Canadians improved on "Foxer," producing a system known as "Cat." It made a screeching noise, not unlike a circular saw.
From German records, 464 Gnats were fired, to give 77 hits. This is only a 16.6 percent success rate, but these bits did include 8 which had their "Foxer's," streamed.
(b) Zig Zagging
The tactic by Convoys of "Zig Zagging," when sailing within U-Boat infested waters, and on moon lit nights, did assist to frustrate stalking Submarines trying to work ahead of a Convoy, to get into a favourable firing position in order to set loose their Torpedoes.
(c) Support Groups
By May 1943, Western Approaches had organised a number of Support Groups which could augment the Convoy ocean escort when a specific Convoy was threatened, and at times an Escort Carrier was included.
By October 1941, high Frequency Directional Finding equipment had been installed aboard Convoy Escorts, and at Coastal Stations. It could be tuned into U-Boats at sea when they broadcast radio messages to Donitz's Head Quarters. Thus Convoy Escorts were given advance warning of U-Boats in the vicinity. By means of cross bearings, the position of the U-Boat could be fixed.
(e) 10cm Radar
July 1942 found Escorts being fitted with the new lOcm Radar, which allowed the position of a surfaced U-Boat to be made up to 4 miles away.
As U-Boats tended to surface at night to charge batteries, or carry out surface attacks on Convoys or Escorts, to assist in combating this phenomenon, the illuminant, christened "Snowflake," said to turn night into day, was developed, and fitted to surface Escorts.
(g) Enigma and Bletchley Park
In the battle against the U-Boats, Enigma played a vital role.
The Government Code and Cipher School, eventually housed at Bletchley Park (at its peak 10,000 people were involved,) had a major task to penetrate the German Cipher System, and specifically crack the "Enigma," machine, around which German codes were built. Intelligence gleaned, would be sent to senior Commanders prefixed with the code word "Hydro," but in June 1941, it was changed to "Ultra."
On the 16th. of August, 1939, Polish intelligence, having constructed a version of "Ultra" passed on a machine to British intelligence.
A Catalog of Electronics Aboard A US Submarine This highly technical page gives a good description of the type of electronic equipment available onboard a US submarine during WW II
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