The Aim-120 AMRAAM (Advanced Medium-Range Air-to-Air Missile) is a modern, Beyond Visual Range (the visual range is about 37 km, or 20 nautical miles), all weather, day-night, Mach 4 air-to-air missile. It started its service as a U.S.A.F. weapon in September 1991, followed by the U.S. Navy in 1993. There is much similarity between the AMRAAM and the Russian R-77 AA-12 Adder (a.k.a. RW-AE), and the French MICA concept missile.
The origins of the Aim-120 lie with the (U.S.A.F.) Medium Range Missile (MRM) Aim-7 Sparrow, and the (U.S. Navy) multiple-launch fire and forget Long Range Missile (LRM) Aim-54 Phoenix. By the 1990s, the USAF reached a decision to manufacture an air-to-air missile for its F-15s and F-16s, that will mimic Phoenix’s multiple-launch and fire-and-forget capabilities, while still being small enough to be equipped onto the F-16’s weapon bays, originally designed for the small Sparrow missile. The AMRAAM was also intended to be the main armament of United States’ future advanced tactical fighter (the F-22 Raptor), and replace the Navy’s existing Phoenix missiles to be used by the fleet’s new air defense aircraft- the F/A-18 Hornet.
Development of the Aim-120 AMRAAM went according to the 1980 “Family of Weapons” agreement- an agreement of collaboration between the U.S. and several NATO nations (expired in 1990). The United States and its other partners worked together on a next-generation air-to-air missile by sharing technology, allowing the United States to develop its desired medium range missile (the AMRAAM), while Europe worked on a short range missile (the ASRAAM). The development of United States’ AMRAAM went according to plans, and it was already deployed in September 1991, firstly utilized by United States’ F-15s. Unlike the AMRAAM, ASRAAM’s project came to a halt when the leaders of the program- Germany and Britain could not agree on its design. This led to the creation of the U.S. Aim-9X Sidewinder, and the European (mostly German) IRIS-T, while Britain continued the development of the ASRAAM on its own, for itself.
The AMRAAM is a fire-and-forget Beyond Visual Range missile, which enables its aircrew to aim and fire multiple missiles at multiple targets simultaneously with no need to guide them to their targets, so the sending aircraft is free to perform any needed evasive maneuver while the missiles fly.
Just before being launched, the AMRAAM receives data from the sending aircraft, which informs it about the target’s location, direction and speed. This information is immediately put to use after launch by the missile, which starts guiding itself towards the target using its inertial navigation system (INS). The INS is a navigation system which calculates the position and velocity of the missile (or other mobile object) in which it operates. It uses acquired data from the beginning of its initiation (in that case, received by the sending aircraft) and with the updated data from its motion sensors, it computerizes on its own its location and velocity. The INS is immune to jamming since it doesn’t depend on external references during motion, however, most AMRAAM missiles can receive periodic updates from the sender (or surrogate) about the target’s location and vector. These guiding updates were proven essential for BVR engagements because the missile’s own active radar works well only in short distances due to its weak power and short range, so until the missile gets close enough to its target it needs the updates.
The Aim-120 made its first kill in December 27, 1992, when a U.S.A.F. F-16C downed with it (in one launch) an Iraqi MiG-25 which violated the southern no-fly-zone. 2 Additional AMRAAM kills took place in 1993 and 1994, each took only one launch. The 100% accuracy of the Aim-120’s first three launches gave it the informal name “Slammer” (though the fourth launch missed, as well as some of the other following launches).
The current operative AMRAAM missiles are the Aim-120A and Aim-120B, which are at the end of their service life, the Aim-120C, which is a special F-22 version missile, with smaller control surfaces, and the Aim-120D, which is the most advanced AMRAAM version (entered full production just recently). The Aim-120 is expected to serve at least until 2020; the approximate year for the deployment of the Joint Dual Role Air Dominance Missile (JDRADM)-United States’ next air-to-air missile which will replace the AMRAAM.