The first truly successful anti-radiation (or anti-radar) missile was the U.S. AGM-45 Shrike first deployed in 1960. Based on the AIM-7 Sparrow body the Shrike (and its developed counter-part the AGM-78 Standard-ARM heavily used by the U.S. Navy during the Vietnam War) proved highly successful and were subsequently utilised by many foreign nations. However, by the early 1980's the twenty year old Shrike was beginning to show its age compared to modern (mainly Soviet) anti-air weaponry. Therefore in early 1983 the U.S. Department of Defence finally gave the go ahead for full production of the follow on weapon, the AGM-88 HARM, High-speed Anti-Radiation Missile. The system became fully operational in both the U.S. Navy and U.S. Air Force in 1984.

Raytheon/TI HARM © Raytheon

The HARM is based on the basic design of the Shrike however it is significantly longer with an increased diameter. The missile is propelled by a Thiokol dual-burn solid rocket allowing a maximum speed of some 2200km/hr to be obtained. As with any of the current anti-radiation weapons (such as Britain's ALARM) the missile utilises a passive radar homing seeker. During the time frame the weapon was deployed there was no standardised weapons bus architecture (as there is now with the MIL-STD-1553B or -1760) and in many cases the launch aircraft's radar detection capabilities were often less than fantastic. To overcome these problems the HARM utilises its own proprietary interface allied to a Command Launch Computer, CLC. Using the CLC the HARM effectively becomes a sensor platform and enables both the aircraft's on-board sensors and any off-board sources to be combined and displayed to the pilot. This comprises one of the three basic operating modes of the HARM, missile-as-sensor enabling self-contained target recognition and automatic prioritisation even when the launch aircraft has no such system itself.

When used as a weapon the missile can be launched in one of two modes, self-protect and pre-emptive. In pre-emptive mode the weapon can be pre-programmed with set of target criteria. Upon launch the missile scans for matching emissions and homes in on the signal. In self-protect mode the missile is directed against a specifically identified threat.

Although HARM has proved itself highly capable (including use in both the Gulf War and Bosnia theatres with great success) it does possess a number of limitations. Of these one of the most basic is the need for specific aircraft compatibility. Also of importance is the seeker and software which are now beginning to show their age. This later problem will be somewhat overcome in the following few years with a number of upgrades. These will see a new wider frequency capable seeker and the introduction of a GPS unit increasing accuracy and enabling the missile to continue to target should the radar be shut down. However even in these cases the weapon shows shortcomings compared to say the British ALARM which offers a full stand-off and loiter capability. Even with these problems the HARM is likely to be around in various forms for many years to come.

* : Note that all ranges quoted are based on mean figures from various data sources. Actual achievable range will depend on a great number of factors and may be no where near those quoted.