The GAU-8(right) is the primary weapon used in the A-10. It can fire up to 4200 rounds per minute. The GAU-8 is capable of firing a family of 30mm ammunition type, including High Explosive Incendiary and Armor Piercing Incendiary rounds.
The gun, which was to become the M-61(below), trailed the development of the M-39, but was ready for operation by 1956. The M-39 represented a substantial improvement over the .50-caliber. The M-39 delivers fifty percent more rate of fire than the .50-caliber, but the M-61 delivers four times the number of rounds in the same amount of time. Equally important, the old machine guns and the M-39 use a reciprocating motion whereas, the M-61 gained reliability in air-to-air operation by employing a rotary motion.
The only aircraft to come close for the air superiority role in conventional warfare was the F-100, which came along too soon for the M-61, therefore was equipped with four M-39s. The F-104 and F-105 were the first two planes equipped with the M-61 Gatling gun. The F-4 was brought into the Air Force inventory for the air superiority role without a gun, but by the onset of the Vietnam War the fighter employed the M-61 Gatling gun carried externally in the SUU-16 pod.
The 40mm Bofors Light Anti-Aircraft Gun(right), based on a Swedish design and built in Canada, served in a number of different theatres during the Second World War. A derivative design is mounted on the AC-130 gunship, with a shortened barrel and a bell-shaped blast deflector. A flexible hood closes the gun mechanism from the outside and allows for cabin pressurization. Starting in November 1969 gunships deployed in Vietnam had two 40mm guns in place of the two aft 20mm Vulcans which originally equiped these aircraft. By 1972 the aft 40mm was replaced by a fixed-mounted 105mm Howitzer on many aircraft.