General Electric

Gau Weapon System

25mm GAU-12/U Equalizer Gun


The five barrel Equalizer Gun was designed to fire the 25mm Bushmaster familv of ammunition to defeat hard ground targets in close-in-air-support by the U.S. Marines Harrier AV-8B vertical take-off aircraft.

The Equalizer GAU-12/U Gun is of Gatling-

Vulcan vintage and more closely resembles in detail design a more recent predecessor, the 30mm Avenger. The fundamental principle of operation is that of a rotary gun where five barrels form a rotating cluster and one barrel fires at a time in a very rapid succession for high firing rates.

However, the gun bolt assemblies use a rotary bolt

Electric Fired Gun

AV-8 Harrier Armament Sysiem head breech lock like the Avenger. It also uses the Avenger scheme of firing pin control and of back-up reverse gun clearing at the end of each burst.

On the other hand, the Equalizer is just a little heavier and a little longer than the old trusty 20mm Vulcan M61A1. The firing rate is 3600 shots per minute but the ammunition has a significantly greater muzzle velocity and terminal effect than the 20mm M50 family of ammunition.


The Equalizer GAU-12/U 25mm gun is used on the Harrier AV-8B aircraft made bv McDonnell-

Douglas for the U.S. Marines.

One of the prime reasons for the Equalizer being on the Harrier reverts back to the time when the Marines were operating their first Harriers AV-BA's on-board Navy carriers. The AV-8 A had revolver guns, the Aden/Dcfa 30mm. They had an unsolvable problem in that the guns could not be safed against cook-off or Radhaz effects.

The Equalizer happened to be available, almost. It was in preliminary dcsity study, until in April 1978 and Independent Research and Development Project was opened by General Electric for a lightwreight proven design, Vulcan-type gun to fire the more effective Bushrnaster ammunition. The Equalizer fired its first shots in December 1978.

It was demonstrated to the U.S. Navv at China T^ike NAS in February 1979. A little over a year later, in July 1980, the first prototype system was installed in a Harrier and flight-fire tested. Flight tests continued at Pax River, NAS and China Lake, NAS for the remainder of 1980 into earlv 1981.

In June 1981, the U.S. Navy contracted General Electric for the first production quantities of the Equalizer GAU-12/U, 25mm armament systems.

Sixty systems have been produced up to mid 1986, and production is continuing at this time.

Equalizer Operation

Firing Cycle. The Equalizer Gun operates the same

Firing Cycle Showing Breech Bolt Motion

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