Could this be the forgotten weapon? 

The Pentagon’s F-35 Joint Strike Fighter team of weapons developers is planning for the aircraft's 25mm Gatling gun to be operational this year, officials said

The weapon has been in development for several years and was successfully test fired on Oct. 30, 2015 in California.

(This first appeared several years ago.)

“This milestone was the first in a series of test flights to functionally evaluate the in-flight operation of the F-35A’s internal 25mm gun throughout its employment envelope,” a Pentagon statement said at the time.

The first phase of test execution consisted of 13 ground gunfire events over the course of three months to verify the integration of the gun into the F-35A, the JSF office said.

More recent activities have included a second phase of testing aimed at further integrating the gun into the airframe during various flight conditions. 

The Gatling gun will bring a substantial technology to the multi-role fighter platform, as it will better enable the aircraft to perform air-to-air attacks and close-air support missions to troops on the ground.

Called the Gun Airborne Unit, or GAU-22/A, the weapon is engineered into the aircraft in such a manner as to maintain the platform’s stealth configuration.

The four-barrel 25mm gun is designed for rapid fire in order to quickly blanket an enemy with gunfire and destroy targets quickly. The weapon is able to fire 3,300 rounds per minute, according to a statement from General Dynamics.

“Three bursts of one 30 rounds and two 60 rounds each were fired from the aircraft’s four-barrel, 25-millimeter Gatling gun. In integrating the weapon into the stealthy F 35Aairframe, the gun must be kept hidden behind closed doors to reduce its radar cross section until the trigger is pulled,” a statement from the Pentagon’s Joint Strike Fighter said, following the 2015 test.

The new gun will also be integrated with the F-35’s software so as to enable the pilot to see and destroy targets using a helmet-mounted display.

Kris Osborn became the Managing Editor of Scout Warrior in August of 2015. His role with Scout.com includes managing content on the Scout Warrior site and generating independently sourced original material. Scout Warrior is aimed at providing engaging, substantial military-specific content covering a range of key areas such as weapons, emerging or next-generation technologies and issues of relevance to the military. Just prior to coming to Scout Warrior, Osborn served as an Associate Editor at the Military.com. Osborn previously served at the Pentagon as a Highly Qualified Expert with the Office of the Assistant Secretary of the Army - Acquisition, Logistics & Technology. Osborn has also worked as an anchor and on-air military specialist at CNN and CNN Headline News. This story originally appeared in Scout Warrior.