For Troops, 'BRRRT' Is Sound Of Music: All About The 'Avenger' In Hormuz

The story of the seven-barrel GAU-8/A Avenger cannon begins with a memo during the Cold War. The A-10 Thunderbolt or 'Warthog' carried the massive cannon to devastating effect in close air support (CAS) roles. Today, it is back in action in the Strait of Hormuz, defying those who wanted to retire it. When fired, the Avenger's signature "BRRRT" sound is instantly recognised by troops who need air support.

Details on the US Air Force (USAF) museum's website said the United States issued a formal request in November 1970 to build a 30 mm rapid-fire cannon for a new CAS platform. The brief said the gun had to kill tanks, punch through hardened positions and survive the low, slow flight regimes expected in contested frontlines.

It wasn't an aircraft looking for a weapon; it was a weapon looking for an aircraft.

By mid-1971, General Electric and Philco Ford had the contract to prototype what was then simply "GAU-8." The gun was only half the job because the USAF also demanded four types of ammo: armour-piercing incendiary, high-explosive incendiary, semi-armour-piercing high-explosive, and a cheaper practice round. Each was meant for a different category of target such as rolling armour, dug-in positions or massed vehicles that needed a short, decisive correction.

The A-X programme that later became the A-10 saw competition between Northrop's A-9A and Republic's A-10A. Before the Avenger was ready, the M61A1 Vulcan was used as a stand-in. A contingency gun also existed, called the GAU-9, which was basically a licensed Oerlikon 304RF built by Hughes. This gun went head-to-head with the GAU-8 in 1973 and lost, while the Avenger stayed.

The GAU-8 first fired in flight in February 1974 and its test crews fired more than 39,000 rounds. The flight envelope was pushed hard from 25,000 feet down to treetop level, with speeds of 135 to 415 knots pulling up to 5 Gs. The aim was to check reliability and survivability on the battlefield.

Later, the Avenger was no longer a gun installed on an airframe, but was the spine of the A-10A. Republic Aviation built the aircraft around the gun, offsetting landing gear, shaping fuselage space, and balancing recoil loads that could nudge the aircraft off its line if the mass ratios were misjudged.

The Avenger went into every production A-10. The earlier Vulcan, useful for testing, became an artifact eventually. Half a century on, the GAU-8/A is back in action in the Gulf of Hormuz. It fires depleted uranium rounds at roughly 3,900 per minute. Redundant hydraulics, a titanium "bathtub" protecting the pilot, and the ability to fly on a single engine give it a survivability that faster, sleeker aircraft could not replicate at low altitude and low speed.