GAU-12 Equalizer

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A GAU-12 cannon as configured for an AV-8B Harrier, with a helmet and two 25mm rounds for size comparison

The General Electric GAU-12/U Equalizer is a 25 mm, five-barrel Gatling gun used by the United States and several other NATO nations.

1 Development
2 Specifications
3 Media
4 External links

[edit] Development

The five-barrel 'Equalizer' cannon was developed in the late 1970s, based on the mechanism of the GAU-8/A Avenger cannon, but firing a new NATO series of 25 mm ammunition.

The GAU-12U cannon is operated by a 15 hp (11 kW) electric motor, in external mounts supplied by a bleed air-drive pneumatic system. Its rate of fire is normally 3,600 rounds per minute, with a maximum of 4,200 rounds per minute.

The Equalizer normally uses PGU-20/U armor-piercing incendiary (API) or PGU-22 or PGU-25 high-explosive incendiary (HEI) ammunition. With a harder-hitting projectile and comparable muzzle velocity, it is more lethal than the older M61 Vulcan, and more effective than the older 30 mm ADEN cannon it replaces.

The current principal application for the Equalizer is the AV-8 Harrier IIs of the U.S. Marine Corps, Italian Air Force and Spanish Air Force. The Harrier II carries the Equalizer system in a pair of pods mounted on the fuselage sides, with the cannon in the port pod and 300 rounds of ammunition in the starboard pod, fed through a bridge at the aft ends of the pods that also contains the drive system for the gun. The complete installation, which includes a double-ended feed system that returns empty cartridges to the magazine, weighs 900 lb (410 kg) empty and 1,230 lb (560 kg) loaded. RAF and Fleet Air Arm Harriers have not adopted the Equalizer for their Harriers. The British had originally planned a pair of ADEN 25 guns (using the same ammunition as the GAU-12/U, but based on the 30 mm ADEN cannon). That gun was canceled in 1999 after protracted development problems, and British Harriers and Sea Harriers have been forced to rely on the older 30 mm gun.

The Equalizer is also used in the AC-130U 'Spooky' gunship (where one cannon is mounted on the port side) and the U.S. Marine Corps LAV AD air-defense vehicle. Other applications have been planned for the GAU-12/U, including a mounting for the AH-1 Cobra attack helicopter.

The latest application of the GAU-12 is for the F-35 Joint Strike Fighter. In the CTOL version of the aircraft it will carry the gun internally, while on the STOVL and CV versions an external podded gun will be available. The major difference between the GAU-12 used on the F-35 and previous applications is the use of a 4-barrel system, rather than the 5 barrels on the standard GAU-12. The 4-barrel version is purported to reduce weight and improve accuracy. This system is currently undergoing testing and qualification.

The weapon's current contractor is General Dynamics Armament Systems.

[edit] Specifications

Type: five-barrel rotary cannon
Caliber: 25 mm (0.98 in)
Operation: electric
Length: 83.2 in (2.11 m)
Weight (complete): 270 lb (122 kg)
Rate of fire: 3,600 - 4,200 rounds per minute
Muzzle velocity: (HEI) 3,400 ft/s (1,040 m/s); (API) 3,280 ft/s (1,000 m/s).
Projectile weight: (HEI) 6.5 oz (184 g); (API) 7.6 oz (215 g)