AIM-4F
The Falcon AIM-4F was the first operational air-to-air guided weapon to enter service with the USAF, becoming operational in 1955. Production began in 1952, and 10 versions were produced for use onF-89, F-101, F-102, F-106 and F-4 aircraft. Over 50,000 Falcons had been built when production ended in 1963. The Super Falcon series was developed to meet mission requirements of the F-106 interceptor.A small number of interim AIM-4E missiles entered service in 1958, but were replaced by the AIM-4F and AIM-4G, which were introduced simultaneously in 1960. These missiles had a higher speed and ceiling,longer range, better seeker systems and more powerful warheads than their predecessors. The AIM-4F has an improved radar guidance system with greater accuracy and increased resistance to enemy jamming.

AIM-4G
The AIM-4G is the infrared-seeking counterpart to the AIM-4F, with a more effective infrared detector.

History
Development started in 1946, when Hughes was awarded a contract to study a subsonic short-range air-to-air missile under project MX-798. The requirement was soon changed to a supersonic missile, to be launchedfrom bombers for self-defense, and development continued under project MX-904 in 1947. At this time, the missile designator AAM-A-2 was also assigned. The first experimental XAAM-A-2 missiles were tested in1949, and in 1950, the missile's platform was changed from bombers to fighters. Now named Falcon, the AAM-A-2 was to become a missile for use by fighter interceptors (F-89, F-102) against relatively slow flyingbombers. In 1951, the USAF began to assign aircraft type designations to its guided missiles, and interceptor missiles were designated as "Fighters". The Falcon became the F-98. The initial XF-98 was designed foruse by subsonic interceptors (like e.g. the F-89), and because of the burn characteristics of its rocket motor wasn't capable of launch from supersonic aircraft. Development of the XF-98 was eventually dropped infavor of a supersonic-launch variant, which was briefly designated XF-104 before it became the XF-98A. The XF-98A prototypes were ground-launched aerodynamic and propulsion test vehicles, while the YF-98A testmissiles were generally air-launched and incorporated a guidance system. After several years of testing, the first production-representative F-98A was eventually delivered in 1954. In 1955, the USAF stopped usingaircraft designations for missiles, and the Falcon was again re-designated. The XF-98A, YF-98A, and F-98A became the XGAR-1, YGAR-1, and GAR-1, respectively.

The GAR-1 was a semi-active radar homing short-range (8 km / 5 miles) intercept missile. It had a Thiokol M58 solid-fuel rocket motor and a rather small 3.4 kg (7.6 lb) high-explosive warhead. It didn't feature aproximity fuse, so the missile had to hit its target to explode. This was not considered a problem for the intended use against large and slow bombers. The GAR-1 became operational with F-89H/J and F-102Ainterceptors in 1956, and about 4000 GAR-1's were produced. The XGAR-1A was a variant of the GAR-1 with a slightly larger airframe and improved motor, and was eventually developed as the GAR-3. The XGAR-1B used thesame airframe as the GAR-1, but was infra-red guided. This version was re-designated as GAR-2. The GAR-1C was a projected variant using the airframe of the -1A and the infrared guidance of the -1B. As such, it wasthe same concept as the later GAR-4.

The GAR-1D was an improved GAR-1, which had better maneuverability because of much larger control surfaces, fitted separately from the wing behind the trailing edge. Its speed was also slightly higher that that ofthe GAR-1. The GAR-1D was the main production model of the original SARH Falcon, with about 12000 missiles built.

The GAR-2 was very similar to the GAR-1D, but used infrared homing instead of SARH, which had the obvious advantage of making the GAR-2 a "fire-and-forget" missile. Like the GAR-1, it became operational in 1956.Normally, interceptor aircraft were equipped with both types of missile, and it was not unusual for a pilot to fire one missile of each variant on a two-missile salvo, to increase the chances of a kill should oneguidance method fail. The GAR-2A variant had an improved IR seeker which could lock on targets in a wider range of background temperatures. More than 26000 rounds of the GAR-2/2A were built.

The GAR-2B was the final development of the infrared Falcon, and is discussed below under its later designation of AIM-4D.

In 1958, Hughes introduced an improved Falcon derivative, initially called the Super Falcon. The first Super Falcon to be developed was the SARH version, designated GAR-3. It had a longer-burning solid-fuel rocketmotor for increased range and higher performance, and a slightly larger airframe with wing-root strakes. The HE warhead was also more powerful, but available sources provide widely differing weight data (between3.9 kg (8.6 lb) and 13 kg (29 lb)). After only 300 GAR-3's had been built, it was superseded in 1959 by the GAR-3A (AIM-4F). The GAR-3A had a new dual-thrust (boost/sustain) M46 rocket motor, and improved SARHguidance with increased accuracy and higher ECM resistance. About 3400 GAR-3A's were produced, and replaced the GAR-1D on most platforms.

The XGAR-4 was the IR homing equivalent of the GAR-3 Super Falcon. It was not built, however, and all IR Super Falcons were produced as GAR-4A (AIM-4G), with the same dual-thrust motor as the GAR-3A. Compared tothe GAR-2/2A, the GAR-4A had an improved IR seeker, which enabled it to lock-on to smaller targets at greater distance. GAR-4A became operational in 1959/60, and about 2700 missiles were built. The GAR-4A replacedall earlier GAR-2/2A missiles.

The XGAR-5 and XGAR-6 were projected nuclear-armed Falcon derivatives, which are briefly discussed in the chapter about the GAR-11/AIM-26 Falcon.

In 1963, all existing GAR-1, -2, -3, and -4 missiles were re-designated in the AIM-4 series, as follows:

The assignment of the plain AIM-4 designator (without suffix letter) to the GAR-1 did not conform to the regulation, which clearly required suffix letters for all variants. I have no explanation why this was done,especially because the new suffix letters didn't match the old ones anyway. The AIM-4D, already briefly mentioned above as GAR-2B, was the final operational development of the AIM-4 Falcon. It combined the smallerairframe of the GAR-2A/AIM-4C with the more modern IR seeker of the GAR-4A/AIM-4G, and was the only Falcon missile designed for use against fighters. About 4000 AIM-4D's were produced, and it became operational in1963. Many earlier AIM-4A/C rounds were also converted to AIM-4D standard.

The AIM-4D was used in combat in South-East Asia by some F-4D Phantoms, which were equipped with special LAU-42/A launchers for this purpose. However, it became soon apparent that the AIM-4D was ill-suited for theclose-range dogfights encountered over Vietnam, and only 5 kills were achieved with the Falcon. The main problem of the missile was seeker cooling. The limited amount of on-board coolant meant that the seeker couldnot be pre-cooled for any length of time, which in turn meant that it had to be cooled more or less shortly before firing, i.e. when close-range combat had already started. This cooling, however, took up to 5seconds which is like eternity in a dogfight, so that most targets were out of reach again when the missile was finally ready. Moreover, when the coolant was exhausted after several aborted launches, the Falcon wasjust useless dead weight, which had to be brought back to base for servicing. Another problem of the Falcon was the lack of a proximity fuse, which made it effectively a hit-to-kill missile. Part of the blame forthe abysmal combat record of the AIM-4D has been given to the fighter pilots, who did not make good use of the Falcon's relatively long lock-on range (9.6 km / 6 miles), which would have made BVR kills possible.However, this blame is somewhat unjustified, because combat rules required visual identification of essentially every potential target before engagement, making the deployment of the Falcon in Vietnam questionableat best. The AIM-4D was gradually withdrawn from use beginning in 1969, and by 1973, the AIM-4D was no longer operational with the USAF.

The final variant of the Falcon was the experimental XAIM-4H, of which only 25 were built in 1970/71. It was an improved AIM-4D with an active laser proximity fuse, a new warhead, and enhanced maneuverability. Theproximity fuse consisted of 4 laser beams in the nose, perpendicular to the missile axis, which effectively created a disc-shaped detection zone around the missile nose. However, because of the Falcon's generalproblems, and because the AIM-9 Sidewinder proved to be an increasingly successful and versatile IR homing missile, the AIM-4H project was aborted in 1971.

AIM-4F Weapon System Evaluator Missile (WSEM): The WSEM is an item of test equipment that is used to evaluate the performance of the fire control system during an airborne simulated attack. This is done bypermanently recording the missile preparation signals on a light-sensitive oscillogram. The signals that are recorded on the oscillogram are recorded in normal missile prelaunch time sequence as either an analog ordigital trace. When the oscillogram is developed, the analysis of these traces verify the correct timing and magnitude of the signals. The prelaunch signals supplied to the WSEM may either perform the identicalfunctions as in a tactical missile, or may be used to serve particular functions in the recording unit of the WSEM. In either case, these signals are recorded on the oscillogram.

"So, In a missile attack, how long will the rails actually stay extended prior to launch. Would the missile stay aboard long enough to acquire?"
According to John Hughes: "The missile electronics are "locked on" the target while the missile is internal. The timing of the firing sequence can change a little, but basically here's how it goes:
* Doors open
* +1 sec, rails extend
* +1.0-1.5 sec, parameter squibs fire followed immediately by rocket motor ignition about 2 seconds later rails retract
* 1 second after that, doors close.
So, the entire sequence from "doors open to doors close" is around 6.0 to 6.5 seconds. Here's a WSEM tape, maybe it'll be clear enough to see the sequence, each vertical solid line is 0.5 seconds."