An air to surface missile, the Air-Launched Anti-Radar Missle or ALARM was designed by British Aerospace. It was originally ordered by the Ministry of Defence in 1983 and, as is usual with defence contracts, took an age to be delivered. ALARM finally went into active service in 1990, in time for the Gulf War where it was one of the most effective weapons.
Ground based radar operators turn off their transmitters once approaching aircraft have been spotted, before any conventional anti-radar missiles can be launched. A fire and forget missile, ALARM gets round this in a unique way. Once launched, it rises to around 40,000 feet, shuts down its engines and deploys a parachute. It then descends slowly, all the while monitoring a large area with its passive radar seeker. Once any aircraft have disappeared, radar operators would turn their installation on again, ALARM then spots the radar signal (a mighty "Over Here"), and locks on, jettisons the parachute and restarts its engine. ALARM can then home in on the target, remembering the location even if the operator turns off transmissions again.
Modern warfare demands air superiority. In the Gulf War it was the RAF Tornado and Jaguar based ALARM that helped force the Iraqi radar sites to stop transmitting, or be destroyed, thus helping to secure free passage for the Allied aircraft.