ASDIC
An active acoustic system for detecting submarines; the letters ASDIC stand for "Allied Submarine Detection Investigating Committee", the part of the Admiralty responsible for the work.
WWI Philip Vassar Hunter collaborated with Admiral W. W. Fisher and William Bragg in a three-man committee to guide the work done by the Admiralty on the development of methods of detecting, locating and destroying submarines. The best known and by far the most fruitful product of this association was ASDIC.
Early work on hydrophones was carried out at the Admiralty Experimental Station, first at Aberdour and later at Parkeston Quay where the active technique, involving sending acoustic signals to be reflected off a submarine, seems to have been developed and the term ASDIC seems to have been first used.
The American name SONAR was later more widely used for this technique