AIM-4 Falcon

The Hughes AIM-4 Falcon was the first operational guided air-to-air missile of the United States Air Force. Development began in 1946; the weapon was first tested in 1949. The missile entered service with the USAF in 1956.

Produced in both heat-seeking and radar-guided versions, the missile served during the Vietnam War with USAF McDonnell Douglas F-4 Phantom II units. Designed to shoot down slow bombers with limited maneuverability, it was ineffective against maneuverable fighters over Vietnam. Lacking proximity fusing, the missile would detonate only if a direct hit was scored. Only five kills were recorded.

With the AIM-4's poor kill record rendering the F-4D ineffective at air-to-air combat, the fighters were modified to carry the AIM-9 Sidewinder missile instead, which was already carried on USAF F-4Cs, USN and USMC F-4 Phantom II and F-8 Crusader jet fighters. The Sidewinder was more effective in the fighter vs fighter role on the F-4 platform, and improved versions continue to serve the armed forces of the United States and numerous allied nations to this day.

Development of a guided air-to-air missile began in 1946. Hughes Aircraft was awarded a contract for a subsonic missile under the project designation MX-798, which soon gave way to the supersonic MX-904 in 1947.

The original purpose of the weapon was as a self-defense weapon for bomber aircraft, which would carry a magazine of three missiles in the rear fuselage, and fire them through a long tube that led through the area that normally held the tail turret. In the case of the B-52, the missile contained a tuner for the bomber's A-3 rear-facing radar, and would follow the signal being reflected off the target aircraft using a semi-active radar homing (SARH) system.

At the same time that the original MX-798 had been released, a specification for a forward-firing missile for fighter aircraft had been released as MX-799. This had progressed to the point of testing prototype rounds, as the AAM-A-1 Firebird, when its subsonic speed and manual guidance were realized to be serious problems.

The project was cancelled, and the recently released MX-904 was redirected to replace Firebird in the anti-bomber role. At this stage the weapon was still designed to be fired out of a tube, now leading from a weapon bay behind the nose-mounted radar with the launch tube exiting below the radar antenna. Instead of a magazine with multiple missiles, three missiles were placed in the tube tip-to-tail.

Housing in a tube presented several problems, but primary among them was that there was no way for the missile's seeker to lock-on before launch. The original concept would be firing against interceptor aircraft that were slowly approaching the B-52 and would be somewhere fairly close to directly behind the aircraft. In the case of a fighter, the target might not be so conveniently located, and with no way to know if it could see the target while inside the tube, this meant it might never lock-on properly.