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

    1. a. A system for detecting the presence of objects at a distance, or ascertaining their position or motion, by transmitting short radio waves and detecting or measuring their return after being reflected; also (secondary radar), a similar system in which the return signal consists of radio waves that a suitably equipped target automatically transmits when it receives the outgoing waves.

1941 N.Y. Times 18 Nov. 8/4 The Navy undertook a special enlistment campaign today to recruit men for training in maintenance of the radio device known as ‘Radar’, which is used to locate ships and aircraft that are hidden by fog or darkness. 1943 News Chron. 9 Feb. 4/6 He described Radar as ‘probably the most dramatic new weapon to come out of this war’. 1943 Times 24 June 4/6 It is expected also to improve ‘radar’, the device for detecting enemy aircraft and ships. 1946 Electronics Apr. 130/3 Frequency-modulation radar determines the distance to a reflecting surface..by measuring the frequency shift between transmitted and reflected waves. 1957 Economist 7 Sept. 831 (Advt.), The performance of modern aircraft must be matched by the radio, radar and Doppler navigational aids necessary for their safe and efficient operation. 1959 K. HENNEY Radio Engin. Handbk. (ed. 5) xxv. 34 Secondary radar, or the ATC radar-beacon system, solves the problem of identification of the individual aircraft in air-traffic control. 1960 J. D. HAIGH Radiolocation Techniques xiv. 213 Another advantage of secondary radar is that if the ‘responding’ transmitter is made to radiate on a frequency different from that of the ‘interrogating’ transmitter, the received picture will be completely free from all permanent echoes and no targets other than those with responding transmitters will be seen. 1962 R. M. PAGE Origin of Radar i. 15 The name ‘radar’ was coined from the words Radio Detection And Ranging by two U.S. Naval officers, F. R. Furth and S. M. Tucker. 1971 D. W. SCIAMA Mod. Cosmol. i. 2 The distance of the Sun is determined most accurately by radar. 1977 C. MCCULLOUGH Thorn Birds xvii. 451 The field which had fascinated him since he first got acquainted with radar: electronics.