The Hughes AIM-4 Falcon was the first operational guided air-to-air missile of the United States Air Force.

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.

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.

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.

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.

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.

Additionally, freed from the tube, the missile's wings were allowed to grow larger and took on the long delta form that it and its various descendants would carry into the 2000s.

The only other users were Canada, Finland, Sweden and Switzerland, whose CF-101 Voodoo, Saab 35 Draken and Dassault Mirage IIIS carried the Falcon.

All of the early Falcons had a small 7.6 lb (3.4 kg) warhead, limiting their lethal radius.

About 2,700 SARH missiles and 3,400 IR Super Falcons were produced, replacing most earlier versions of the weapon in service.

An effort to address the limitations of AIM-4D led to the development in 1970 of the XAIM-4H, which had a laser proximity fuze, new warhead, and better maneuverability.

The Falcon, already operational on Air Defense Command aircraft, was designed to be used against bombers, and its slow seeker cooling times (as much as six or seven seconds to obtain a lock on a target) rendered it largely ineffective against maneuvering fighters.

[2] (The Falcon was also experimentally fired by the F-102 Delta Dagger against ground targets at night using its infrared seeker.)

The weapon was unpopular with pilots from the onset and was supplemented or partially withdrawn in 1969, to be replaced in the F-4D by the Sidewinder after retrofitting the proper wiring.

Used from 1965 through 1972 in Vietnam, Falcons achieved their only kills during Operation Rolling Thunder (1965–68) , with only 5 successful hits scored after 54 launches in aerial combat.