Sonar (O.E.D., on line):
orig. U.S.

   A system for use under the sea in which the audible or high-frequency sound reflected or emitted by an object in the sea is used to ascertain its position, nature, or speed; (an) apparatus used for this; also in extended use, a system in which the position of an object in air or water is ascertained by reflected ultrasound, e.g. as used by bats and in diagnostic medicine.  Freq. attrib. Cf. ASDIC (see quot. 1963).

Examples:

  1946 U.S. Navy Press Release 6 Apr. 1 The word ‘sonar’ was coined from abbreviations for sound, navigation and ranging, and includes various types of underwater sound devices used in detecting submarines and other submerged objects and in obtaining water depths. 1952 [see ASDIC]. 1961 W. N. KELLOGG Porpoises & Sonar (1962) iv. 48 The idea that sonar is systematically used by the great whales and porpoises is..a new and intriguing thought. 1963 Times 2 Feb. 5/2 In order to conform with NATO practice, the name Asdic..has been superseded by the word Sonar, the Admiralty announced yesterday... In future Asdic ratings will be known as Sonar operators. 1968 M. WOODHOUSE Rock Baby xiii. 129 Bats swooped past my head, bouncing their tiny high-pitched sonar echoes off me. 1971 Hi-Fi Sound Feb. 63 (Advt.), The photograph shows Ferrograph recorders at work in the Sonar Room aboard the Hunter Killer nuclear-powered Submarine H.M.S. ‘Churchill’. 1971 New Scientist 3 June 568/1

Comment:

The standard method of detecting submerged submarines is by sonar, either active or passive. 1973 Brit. Med. Jrnl. 6 Oct. 28/1 The ‘in utero’ crown-rump length of the fetus may be determined by sonar in the first trimester of pregnancy. 1974 Sci. Amer. Mar. 120/2 Frequency-modulation sonars..can exploit a Doppler signal to measure speed. 1979 Ibid. Feb. 67/1 (Advt.), These unique sonar cameras send out an inaudible sound signal that bounces off the subject and returns to the camera, in milli-secondsand the lens automatically rotates to perfect focus.

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