Skynight

Tail Warning Radar didn't allow aircraft to fire at someone trailing them, they simply told the pilot that he had someone on his tail.

However, this lead to the enemy developing receivers that could home in on the transmissions the radars produced (the Germans did this to the British, in WWII http://en.wikipedia.org/wiki/Monica_radar).

Modern combat aircraft reverse this tactic. They have receivers that allow them to detect enemy radar transmissions coming from anywhere around them.

See http://en.wikipedia.org/wiki/Radar_Warning_Receiver for more information.