A U.S. Marine Corps F-35B Lightning II suffered a self-inflicted cannon-shot wound during live-fire exercise in Arizona on March 12. The pilot was unhurt and landed safely, and damage, initially reported as up to $2.5 million, was later reassessed at less than $600,000.
One shell from the fighter’s externally mounted GAU-22 cannon exploded immediately after leaving the muzzle, damaging the stealth fighter’s fuselage. It remains unclear whether the pilot was triggering the GE-designed General Dynamics four-barrel rotating “gatling” cannon at the time, or if the discharge was accidental.
On the F-35B and C naval variants, the 25-mm GAU-22 is mounted on a pod slung under the fuselage, well aft. Meant for both close-in air-to-air dogfighting and ground attack, it fires at a rate of 3,300 rounds per minute and carries 220 rounds—just four seconds’ worth. The U.S. Air Force F-35A carries its GAU-22 internally and fires through an opening above the wing on the left side of the aircraft.
The ammunition in the Marine F-35B was reported by Military.com as PGU-32 semi-armor-piercing high-explosive incendiary tracer, meaning each shell emits a visible glow as it travels toward the target so the pilot can track it. Cannon shells are meant to explode on impact, but this one appears to have detonated prematurely—extremely prematurely. Muzzle velocity of the GAU-22 is reported as 3,280 feet per second, so if the round blew under the fuselage, it would have done so around 1/200th of a second after leaving the muzzle.