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30 mm aircraft armament system.

In 1968 General Electric (GE) (now Martin-Marietta
Armament Systems), began work as a private venture on a
cannon specifically designed for killing tanks and
other hard skinned ground targets. Like their earlier
family of Vulcan cannon, the weapon used the same
Gatling gun principle, but the calibre was increased to
30 mm and the number of barrels to seven. From the
outset, because of the cannon's physical size and
power, it was clear that any future close air support
aircraft would have to be virtually designed around
such a weapon.
  In 1971 GE was awarded a contract to develop the 30
mm cannon now designated GAU-8/A in order to provide
the main armament system for the new close air support
aircraft which was at the time in the competitive stage
of development. In 1972 Fairchild won the aircraft
competition, and in 1973 was awarded the contract to
produce prototypes of the A-10 with the GAU-8/A cannon

The GAU-8/A Avenger weapon system, which has been
specifically designed for the A-10 Warthog close air
support combat aircraft, consists of four major
assemblies: the GAU-8/A cannon itself, drive system,
feed and ammunition storage system, and an electrical
control system. The total system is 6.4 m long and when
fully loaded weighs 1723 kg. Access to the system is
through a series of doors in the bottom of the fuselage.
  The GAU-8/A cannon on its own is 2.9 m long, has a
maximum diameter of 356 mm, and weighs 281 kg. It is a
30 mm seven-barrelled, Gatling type cannon having a
rotary action powered from a twin aircraft hydraulic
supply and has a firing rate of 1800 or 4200 rds/min.
All barrels are rigidly clamped together and attached
to the forward end of the breech rotor which rotates in
a stationary housing. Each of the cannon's barrels
fires only once during each revolution of the barrel
cluster, and is attached to the cannon rotor by quick
release interrupted lugs.
  The HEI round employs a standard M505 fuze and
explosive mixture with a body of naturally fragmenting
material that is effective against lighter vehicle and
material targets. The API round has a lightweight body
which contains a sub-calibre high density penetrator of
Depleted Uranium (DU).
  In addition to its penetrating capability DU is a
natural pyrophoric material which enhances the
incendiary effects. The TP projectile simulates the
exterior ballistics and provides a ballistic match to
the HEI round and is used for pilot training and gun
peacetime but is the standard war ammunition used
against armoured vehicles. The muzzle velocities of the
various rounds are as follows: API 1030 m/s and TP and
HEI 1036 m/s.

Calibre: 30 mm
No of barrels: 7
Length: 2.9 m
Weight: 281 kg
Rate of fire: 1800 or 4200 rds/min selectable
Muzzle velocity: 1030 or 1036 m/s depending on
Avenger weapon system
Length: 6.4 m (including cannon barrels)
Diameter: 850 mm (ammunition drum)
Number of guns: 1 x 30 mm barrelled cannon
Ammunition capacity: 1350 rds
Lug spacing: N/A
  (loaded) 1723 kg
  (unloaded) 785 kg