The AIM-120 Advanced Medium-Range, Air-to-Air missile is a new generation air-to-air missile. It has an all-weather, beyond-visual-range capability and is scheduled to be operational beyond 2020. The AMRAAM is being procured for the U.S. Navy, Air Force and allies of the United States. In addition to providing an air-to-air capability, AMRAAM also provides air defense support.
The AIM-120A is the baseline version of the AMRAAM. It is powered by a solid-propellant rocket motor in a WPU-6/B propulsion section. Before launch, the launching aircraft's fire control system programs the missile's inertial autopilot in the WGU-16/B guidance unit to bring it into a homing basket in the vicinity of the target. The autopilot can receive mid-course updates from the aircraft via a data link. The AMRAAM's WCU-11/B control section controls the missile in flight with the four movable tail fins. As soon as the target is within range, the AMRAAM activates its active radar seeker for autonomous terminal homing.
The AMRAAM P3I (Pre-Planned Product Improvement) program led to the AIM-120C. The major new feature of the basic AIM-120C (P3I Phase 1) is its clipped wings and fins. Although this feature was introduced to allow carriage in the internal weapons bays of the F/A-22 Raptor, the missile can also be used from other AMRAAM-capable aircraft. The guidance unit of the AIM-120C is upgraded to WGU-44/B standard.
This upgrade is called P3I Phase 4, formerly known as AIM-120C-8, and it features a two-way data link, more accurate navigation using a GPS-enhanced IMU (Inertial Measurement Unit), an expanded no-escape envelope, improved HOBS (High-Angle Off-Boresight) capability, hardened design for internal weapons bay carriage, and a 50% increase in range. It is a joint U.S. Air Force / U.S. Navy project.