"This work, for the Anti-Submarine Division, was undertaken in utmost secrecy, and used quartz piezoelectric crystals to produce the world's first practical underwater active sound detection apparatus. To maintain secrecy no mention of sound experimentation or quartz was made - the word used to describe the early work ('supersonics') was changed to 'ASD'ics, and the quartz material 'ASD'ivite. From this came the British acronym ASDIC. In 1939, in response to a question from the Oxford English Dictionary, the Admiralty made up the story that the letters stood for 'Allied Submarine Detection Investigation Committee', and this is still widely believed, though no committee bearing this name has ever been found in the Admiralty archives."
During World War II Americans developed a similar underwater active sound detection system which they called SONAR, and this term eventually replaced the British ASDIC.