The U.S. Air Force is testing the internal integration of a four-barrel Gatling gun into the F-35A Joint Strike Fighter.

The first phase of ground testing began last month on an F-35 test aircraft -- the AF-2 -- at the Edwards Air Force Base Gun Harmonizing Range. Flight tests could begin in late September.

The Gatling gun is the GAU-22/A, which fires 25 millimeter rounds, the Air Force said.

"As an Air Force pilot, it's going to be one more thing that I can select to either strafe air-to-ground targets or shoot as an air-to-air weapon," said Maj. Andrew Rollins, 461st Flight Test Squadron, assistant director of operations. "The GAU-22/A uses a 25mm shell, which is significantly more powerful than what I've been used to in legacy aircraft, the F-16 the F-15E, F-15C - all those aircraft use a 20mm shell."

The first shots fired in initial testing were non-exploding PGU-23/U practice rounds. An operational gun capability will be added with a future block of software, which is in the beginning stages of testing at Edwards.

"The tricky part about this test phase is that the gun will never operationally fire on the ground," the Air Force said. "To conduct the test, they have to use software to bypass interlocks and "fool the aircraft to make it think it's in the air."

The use of the GAU-22/A Gatling gun on an F-35 is not new. Navy and Marine Corps F-35 variants carry the gun externally as a weapons pod. Internal carrying of the weapon helps to keep the stealth jet hidden from radar detection.

AF-2, the F-35A test aircraft that famously lost the dogfighting trials against an older F-16 fighter earlier this year, is now used for ground tests of its GAU-22/A automatic cannon, mounted above its port air inlet.