Allied forces built the chain home radar in 1938 to detect German air activity during WWII. Radar, an acronym for radio detection and ranging, provided a new means of identifying enemy air and ground units at long distances through fog, smoke and darkness. Radar provided information as to the distance, speed, and direction of its target. In the 1990's researchers developed a way to neutralize the effect of radar. Stealth planes minimized reflective surfaces, rendering them invisible to radar.