The GAU-13 was developed in the late 1970s for use in gun pod applications for fighter aircraft and attack aircraft use, primarily for air-to-ground and anti-tank attacks. The GAU-13/A is a four-barreled rotary cannon based on the mechanism of the larger GAU-8, sharing the same massive 30 mm ammunition. Like the Avenger, it has a double-ended feed system with reverse clearing to remove unfired rounds. Unlike the GAU-8, however, it is pneumatically driven, giving it a rate of fire of 2,400 rounds per minute. Minimum time between stoppages is estimated at 32,000 rounds, making it a very reliable weapon. The GAU-13/A uses the same range of PGU-13High Explosive Incendiary and PGU-14Armor-Piercing Incendiary rounds as the Avenger. Despite its somewhat lower rate of fire compared to the seven-barreled Avenger, it is an immensely powerful weapon. The principal application for the GAU-13/A was the GPU-5/A gun pod. The pod is 4.3 m long and can be mounted on any standard NATO 762 mm suspension lugs. It holds 353 rounds of ammunition, enough for approximately nine seconds of continuous fire. The GPU-5/A weight is 600 kg empty and 841 kg fully loaded. The pod is completely self-contained. The GPU-5/A was intended for carriage on a wide range of U.S. tactical aircraft, including the F-15 Eagle and F-16 Fighting Falcon. In the mid-1980s the USAF considered a specialized variant of the F-16 for the close air support mission, using the GPU-5, as a substitute to or adjunct for the A-10 Thunderbolt II. The GPU-5 pod, however, proved unsatisfactory in service. It was briefly tried on some Air National GuardF-16 Fighting Falcons during the 1991 Gulf War, but was removed from service after barely a day of combat use because of its very poor accuracy. Despite the cannon's impressive ballistic characteristics, the pylon mounting was not sufficiently rigid to prevent deflection, and the weapon's heavy recoil exacerbated the problem by causing pylon misalignment. Further, the GPU-5 was not integrated into the F-16's sighting system. The GPU-5 is no longer in U.S. service, although some ThaiF-5E Tiger II aircraft still carry the weapon; it was also tested on the F-20 Tigershark. In Fall 1995, the U.S. Marine Corps conducted a trial of the GPU-5 on the LCAC-66, as a potential weapon to provide suppressive fire for landing forces. The pod was mounted on a standard MAU-12 bomb rack, itself mounted in a standard cargo container. It was believed that four such containers could then be carried on the LCAC. The resulting combination was referenced as the Gun Platform Air Cushion. By 1997, the Marines had reportedly acquired the USAF's entire stock of GAU-13/A cannons and GPU-5 pods as surplus. Besides the GPAC, the GAU-13/A was also touted as possible armament on ships and ground vehicles such as the LAV-25.
