List of British Asdic systems
was British version of sonar developed at the end of World War I based on the work of French physicist Paul Langevin and Russian engineer M. Constantin Chilowsky. The system was developed as a means to detect and locate 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 s and small escorts like P and PC-class sloops | |
| Type 119 | 1930 | s | |
| Type 121 | Tested 1931 in | First production retractable dome | Fitted in D,, F, and G-class destroyers, some cruisers and the sloop |
| 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,,,,, and 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 | Retractable | , L, and s |
| Type 141 | ? | No dome, but some modified with British dome as Type 141A | American QCJ/QCL system in Lend-Lease s, modified with British range and bearing recorders |
| Type 144 | Trials in 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, May 1943 | ? | Designed to work with Squid |
| Q attachment | 1943 | NA | Depth-measuring set with 3° horizontal beam, modification to existing systems |