Applications
The Vulcan was first used in the F-104 Starfighter. The gun was also used in the F-105 Thunderchief in combat against Soviet-designed MiG fighters over Vietnam. It was installed in the Air Force's A-7D version of the A-7 Corsair II where it replaced the Naval versions' standard dual cannon, and subsequently adopted by the Navy on the A-7E and in future fighters. Significantly it was designed into the F-4E Phantom II; no previous F-4 had a cannon as it had been believed that missiles had made guns obsolete. Combat experience in Vietnam showed that a gun could be more effective than guided missiles in many combat situations, and that an externally carried gun pod was less effective than an internal gun.
The Vulcan was later fitted into the weapons bay of some F-106 Delta Dart models and the F-111 Aardvark. It was also adopted as standard in the teen-series air superiority fighters, the F-14 Tomcat, the F-15 Eagle, F-16 Fighting Falcon and F/A-18 Hornet. Other aircraft include the Italian/Brazilian AMX International AMX (on Italian aircraft only), and the F-22 Raptor. It was fitted in a side-firing installation on the AC-119, some marks of the AC-130 gunships, and was used in the tail turrets of both the Convair B-58 Hustler and Boeing B-52H Stratofortress bombers. Japan's Mitsubishi F-1 carried one internally mounted JM61A1 Vulcan with 750 rounds.
Two gun pod versions, the SUU-16/A (also designated M12 by the US Army) and improved SUU-23/A (US Army M25), were developed in the 1960s, often used on gunless versions of the F-4. The SUU-16/A uses the electric M61A1 with a ram-air turbine to power the motor. This proved to cause serious aerodynamic drag at higher speeds, while speeds under 400 miles per hour (640 km/h) did not provide enough air flow for maximum rate of fire.
The subsequent SUU-23/A uses the GAU-4/A self-powered Vulcan, with an electric inertia starter to bring it up to speed. Both pods ejected empty cases and unfired rounds rather than retaining them. Both pods contained 1,200 rounds of ammunition, with a loaded weight of 1,615 pounds (733 kg) and 1,720 pounds (780 kg) respectively. During service in the Vietnam War the pods proved to be relatively inaccurate: the pylon mounting was not rigid enough to prevent deflection when firing, and repeated use would misalign the pod on its pylon, making matters worse.
A variant with much shorter barrels, designated the M195 was also developed for use on the M35 Armament Subsystem for use on the AH-1G Cobra helicopter. This variant fed from ammunition boxes fitted to the landing skid and was developed to provide the AH-1 helicopter with a longer-range suppressive fire system before the adoption of the M97 Universal Turret mounting the M197 cannon.
The M61 is also the basis of the US Navy Mk 15 Phalanx CIWS system and the M163 VADS Vulcan Air Defense System (the M168 variant is used).
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