The Air Launched Anti-Radiation Missile (ALARM) is designed to destroy or suppress the use of enemy ground-based air-defence radar systems.
The BAE Systems weapon was selected ahead of the US High-Speed Anti-Radiation Missile (HARM) following a two-way contest for the MoD order during the 1980s.
It first saw service during the Gulf War of 1991 and has been in the weapon inventory of the Tornado ground attack aircraft ever since, including the latest GR4 model.
Combinations of between two and seven missiles can be carried on each aircraft. Since its original entry into service, radars have become increasingly more sophisticated in their ability to avoid detection and attack by anti-radiation weapons such as ALARM; consequently, the missile has been upgraded and the improved capability ALARM has entered service with the RAF's Tornado squadrons.
The ALARM operates by homing onto the radar energy being emitted by the target radar in several ways. If the target is active and emitting radiation when the missile is launched, the ALARM will fly direct to the target. If the targeted radar is quiet when the missile is launched, the ALARM will fly to a pre-set point above the target and loiter under a parachute in the area until the radar switches on. It will then eject the parachute and home onto the target. In Area Suppression mode the missile can be fired in the direction of radars whose positions are unknown and it will engage the highest priority target for attack. In Direct mode the missile is pre-programmed with threat radars and executes a box-search for them after launch, homing onto the highest priority target.
The missile can be pre-loaded with a prioritised file of hostile radars, for which it will search after launch.
Some Tornado F3s were modified to carry ALARMs for operations over Iraq during 2003.