Radar (short for Radio Detection and Ranging) is a radio-based method for detecting the existence of distant aircraft. The term was coined at the beginning of World War II. Radar was invented by the British in the 1930s and put in place just in time to win the Battle of Britain in 1940 by spotting the exact location of fleets of Luftwaffe bombers and sending fighters to intercept them. .
Radar works by bouncing radio waves off distant objects (such as aircraft) and timing their reflection. Conventional radar uses wavelengths on the range 40mm-60mm.
Sometimes radar "tracks" are misread, as in the American shooting down of Iran Air Flight 655 in 1988, killing all of the 290 passengers and crew aboard. Airborne dust and the fact that the plane was approaching head-on misled the radar crew. They also claimed the plane was four miles outside the commercial flight path.