List of British Asdic systems

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Asdic was invented by the British at the end of World War I as a means to detect submarines by their reflection of sound waves. By the start of World War II in 1939, most British destroyers and smaller vessels were fitted with it in a variety of different sets.

Name Date of Introduction Dome Notes
Type 112 1920 Fitted to some V and W-class destroyers and small escorts like P and PC-class sloops
Type 119 1930 B-class destroyers
Type 121 Tested 1931 in Woolston First production retractable dome Fitted in D, E, F, and G-class destroyers, some cruisers and the sloop Enchantress
Type 122 Detachable Designed for trawlers and other auxiliaries with a turbo alternator
Type 123 1934 Detachable Replaced Type 122, designed for ships with a high-frequency motor alternator
Type 124 1934 Retractable C, H, I, J, K, and Tribal-class destroyers, some sloops and older destroyers. First system with a range recorder
Type 127 1937 As per Type 122 Designed for sloops, but widely fitted in frigates and older destroyers. Electronics as per Type 123
Type 128 Tested 1937 in Acheron Retractable A, L, and Hunt-class destroyers
Type 141  ? No dome, but some modified with British dome as Type 141A American QCJ/QCL system in Lend-Lease Town-class destroyers, modified with British range and bearing recorders
Type 144 Trials in Kingfisher in 1941 Retractable First set specifically intended for ahead-throwing weapons like Hedgehog
Type 145 1942? Detachable Like Type 144, but intended for slower escorts
Type 147 Sea trials aboard Ambuscade, May 1943  ? Designed to work with Squid
Q attachment 1943 NA Depth-measuring set with 3° horizontal beam, modification to existing systems



  • Brown, David K. (2007). Atlantic Escorts: Ships, Weapons & Tactics in World War II. Annapolis, Maryland: Naval Institute Press. ISBN 978-1-59114-012-2.