GAU-8 "Avenger"

The AN/GAU-8 30mm Avenger seven-barrel gatling gun, mounted only on the A-10 attack jet, is a 30mm, 7 barrel gattling
gun used primarily in the air to ground role as a soft target killer and tank buster. This aircraft is used for close-air support in
attacking ground threats such as armored tanks and vehicles, and also serves as a forward air control observer for sighting
ground threats and directing air strikes against enemy targets. The gun, mounted in the fuselage nose of the A/OA-10
Thunderbolt, is produced by [ex General Electric] Martin Marietta Armament Systems. It fires 1,800 rounds per minute, with
the higher 4200 rd/min rate having been deleted in the 1980s.

The gun fires a mix of both high explosive incendiary (HEI) and armored piercing incendiary (API) ammunition. The PGU-13/B
HEI High Explosive Incendiary 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 PGU-14/B API Armor Piercing Incendiary
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 PGU-15/B TP Target
Practice projectile simulates the exterior ballistics and provides a ballistic match to the HEI round and is used for pilot training.

A typical combat load for the GAU-8 would include 1,100 rounds of 30mm high explosive or armor piercing ammunition. The
30mm API is mixed with 30mm High Explosive Incendiary (HEI) at the factory and is called Combat Mix Ammunition. The
ratio of API to HEI rounds in the Combat Mix is 4:1. Combat mix is a sequential mixture of DU and HEI rounds in which 1
HEI round followed by 5 DU rounds are fired by the AN/GAU-8 gatling gun, followed by one DU round. DU is the primary
munition for the A/OA-10 in a combat environment.

Depleted uranium results from the enriching of natural uranium for use in nuclear reactors. Natural uranium is a slightly
radioactive metal that is present in most rocks and soils as well as in many rivers and sea water. Natural uranium consists
primarily of a mixture of two isotopes (forms) of uranium, Uranium-235 (U235) and Uranium-238 (U238), in the proportion of
about 0.7 and 99.3 percent, respectively. Nuclear reactors require U235 to produce energy, therefore, the natural uranium has
to be enriched to obtain the isotope U235 by removing a large part of the U238. Uranium-238 becomes DU, which is 0.7
times as radioactive as natural uranium. . Since DU has a half-life of 4.5 billion years, there is very little decay of those DU
materials. When manufactured as 30mm rounds, each DU projectile contains approximately 4,650 grains [0.66 pounds (lbs)]
of extruded DU, alloyed with 0.75 weight percent titanium. The projectile is encased in a 0.8 mm-thick aluminum shell as the
final DU round.

During Operation DESERT STORM the Air Force fired 30mm Armor Piercing Incendiary (API) munitions using a depleted
uranium [DU] penetrator slug from the GAU-8 Gatling gun mounted on the A-10 Aircraft. The 148 A-10s that deployed to
Saudi Arabia flew 8,077 combat sorties. The Air Force fired a total of 783,514 rounds of 30mm API in the Gulf War. Since
each round contains approximately 0.66 pounds of DU, the Air Force expended a total of 259 tons of DU in the Gulf. The
armor-piercing capability of the DU projectiles fired from A/OA-10s proved exceptionally effective in countering threats from
the Iraqi tanks so that a successful ground offensive could then be achieved.

At times 30mm DU rounds misfire in the A-10’s GAU-8 cannon. These "hangfires" have to be cleared and removed from the
gun barrel, potentially exposing ground crews to airborne DU. Technical data available to maitenance crews does not provide
an accurate means for determining the status of rounds in an unsafe/jammed gun, and revisions are in progress.