When the Gulf War began in 1991, the US military deployed over 132 Thunderbolt II close air
support aircraft armed with a powerful 30-millimeter GAU-8 Avenger rotary cannon with a fire rate
of over 3,900 rounds per minute.
The GAU-8 is so powerful that it requires a meticulous approach to operate correctly.
As footage from the US military shows, the ammunition feed system is double-ended, and
allows spent cases to return to the munitions drum without affecting the aircraft's center
of gravity.
A pilot could empty the 1,350-ammunition drum in less than 20 seconds, and despite knowing
the tremendous firepower he had at his hands, Captain Robert Swain could not believe what
he did over the skies of Kuwait on February 6, 1991.
As the captain encountered several Iraqi helicopters close to his location, he engaged them without
hesitating.
In fact, one single burst of his Avenger cannon was enough to tear apart any Soviet-made helicopter…
The A-X Program On September 8, 1966, General John P. McConnell,
the Chief of Staff of the Air Force, expressed his desire to develop a specialized close
air support aircraft.
By December, a Requirements Action Directive or RAD was issued for a dedicated CAS close
air support aircraft for the Air Force.
This led to the creation of the AX or Attack Experimental program office.
The Vietnam War was in full swing at the time, and the Army and the Marines desperately needed
all the air support they could muster to fight off the Viet Cong guerrilla and the well-disciplined
North Vietnamese Army.
The Air Force eventually realized that this new aircraft would also be needed if a war
broke out with the Soviet Union in opposition to the Warsaw Pact.
In that case, NATO countries would need to respond with an aircraft capable of attacking
infantry formations, armored transports, and tanks under any weather conditions.
This led the Air Force to issue a more detailed request for proposal for the AX Attack Experimental
aircraft in early May of 1970.
And one essential component was to have a gun capable of tearing apart advancing Soviet
armor.
GAU-8 Rotary Cannon While the defense contractors were hard at
work developing the CAS aircraft, the US Air Force issued another request for proposal
and competition to establish the main armament of the AX platform: a gigantic 30-millimeter
rotary cannon.
If successful, the AX would become one of the few combat aircraft fitted with such a
heavy and powerful armament, and the reasoning behind it was directly related to the ongoing
Vietnam War.
The 20-millimeter M61 Vulcan cannons mounted on numerous fixed-wing and rotary-wing aircraft
of the Navy, Air Force, Army, and Marines had proven successful against enemy aircraft
and ground targets, but it was not without issues.
The Vulcan lacked the required power to put armored targets out of commission, including
the Soviet and Chinese tanks employed by the North Vietnamese military and other armored
vehicles.
Based on that combat experience, a more significant caliber weapon was required to destroy hostile
armor and a specific range from which the aircraft could fire accurately.
Consequently, the RFP specified that the 30-millimeter cannon had to have a desired fire rate of
over 4,000 rounds per minute and high muzzle velocity.
Of all the defense contractors, only Philco Ford and General Electric offered competing
designs in June of 1971.
The prototype gun was designated GAU-8, and the USAF called for the additional development
of four different types of ammunition for the cannon: Armor Piercing Incendiary, Target
Practice, High Explosive Incendiary, and Semi-Armor Piercing High Explosive rounds.
Testing the Rotary Cannon The first in-flight testing of the GAU-8 cannon
took place in February of 1974.
It was followed by a second test in June of 1974, when it was fired for the first time
with combat ammunition.
More than 40,000 rounds of different types of ammunition were fired during 60 test flights
to thoroughly analyze the cannon’s performance, and it was also tested with different flight
profiles to study how it fared for the CAS role.
Moreover, the GAU-8 was also tested during aircraft maneuvers such as rolls, pitches,
and yaws.
The mighty cannon was tried at altitudes ranging from just 100 feet to over 25,000 feet, with
up to five Gs.
The gun was also fired at 155 miles to 477 miles per hour.
The trials were successful and helped engineers improve the performance of the rotary cannon.
The GAU-8 only jammed once due to residue buildup on the canopy and other minor issues
with the gun’s ingestion into the engines.
When the GAU-8 became operational in 1977 with Republic’s A-10 Thunderbolt II -the
result of the AX platform- the cannon was dubbed the Avenger.
Inspiration The design of the GAU-8 was inspired by the
Gatling Gun, which was used for the first time during the last days of the American
Civil War, and it has seven barrels mounted around the periphery of a cylinder.
Still, while the 19th-century Gatling Gun was hand-cranked, the GAU-8’s cylinder is
rotated by two hydraulic motors, making it a repeating weapon with lethal firepower.
The rotary cannon measures 19.5 feet from the muzzle to the rear of the ammunition system,
which measures 34 inches in diameter and is 71 inches long.
Plus, it weighs 620 pounds, but the drum and the feed system with maximum ammunition increase
the load to over 4,030 pounds.
Firing the Avenger The Avenger can hold up to 1,174 rounds, and
its power is provided by twin hydraulic motors that allow it a fire rate of 2,100 rounds
per minute under its low setting and 4,200 rounds per minute as its maximum.
Still, the Avenger is almost fixed to a fire rate of 3,900 per minute to prevent overheating
and other mechanical issues.
The gun’s fire rate is so fast that the magazine runs dry in over 18 seconds of sustained
fire.
Pilots are trained to fire one- and two-second bursts to preserve ammunition and avoid overheating.
This firepower puts enormous stress on the seven barrels of the GAU-8.
The expected barrel life is over 20,000 rounds, and the entire weapon system, from the gun
barrels to the motors and magazine system, must be meticulously checked after every operation
to ensure there are no problems with the double-ended feed approach.
In addition, the gun requires strict maintenance, especially when it comes to loading it with
new ammunition.
Footage taken from the Idaho Air National Guard 124th Fighter Wing shows the process
with high fidelity.
The servicemen of the 124th Aircraft Maintenance Squadron are seen unloading the GAU8 ammunition
from a Thunderbolt and inspecting it, and the maintenance squadron then loads the GAU8
feed system with fresh ammunition.
Besides the incredible rate of fire of the Avenger, it is also highly accurate and can
hit all its targets within its effective range of 4,000 feet with more than 80 percent accuracy.
Its muzzle velocity is 3,320 feet per second, but it varies according to the type of ammunition
used.
In addition, the gun is mounted laterally off-center, near the port side of the fuselage
centerline, to keep the balance of the aircraft and prevent the Avenger’s recoil from pushing
off the aircraft from its target when firing.
Finally, the barrel is located below the Thunderbolt II’s center of gravity to further stabilize
the aircraft, and the average recoil force is over 10,000 pounds of force.
To this day, over 700 Thunderbolt IIs have been produced, and the aircraft remains in
service.
Its effectiveness and acclaim lay primarily on its impressive GAU-8 Avenger 30-millimeter
cannon.
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