The AGM-136A Tacit Rainbow was a United States military anti-radiation missile program run from 1982 to 1991. The requirement was for a low-cost air-launchable system to aid in the destruction of enemy air defense networks. The proposed unit would combine elements of cruise missiles and UAVs, it would be launched in large numbers by heavy bombers, fighters, or possibly mass ground launch systems. The missiles would fly in advance of manned aircraft up to 450 km (280 mi) to pre-programmed target zones and patrol there until enemy radar sources were detected which would then be destroyed, acting as a loitering munition. This extended patrol time on target ("loiter time") was the key feature of the new system, a persistent anti-radiation missile (PARM) as opposed to a HARM.