When machine guns were first mounted to aircraft at the dawn of aviation, tacticians quickly realized that in order to score kills any weapon needed to get the maximum number of rounds on target as fast as possible. High rates of fire were the natural solution, but they also proved to be bullet hogs.
One German designer, however, found a different approach to the problem. Create two machine guns in one. The result, the 7.92mm Gast Machine Gun.
Looking more like a wheeled hand cart than weapon, the Gast was odd, innovative and actually worked.
Developed towards the end of 1917, the Gast is a double-barreled machine gun fed from a pair of pan magazines, each holding nearly 200 rounds. When fired, the Gast had a rate of fire of 1,300 rounds per minute at a muzzle velocity of nearly 3,000 feet per second.
The single receiver held the two barrels and breach mechanism. When loaded, charged and fired, one Gast barrel would recoil slightly, actuating a lever that loaded a round into the opposite barrel extension. When that round was fired, the second barrel would recoil, levering a new rounds into it's opposite.
Plans were made to create a 13 mm heavy machine gun version of the Gast, but it never saw completion. The Gast in 7.92 mm was initially ordered for 3,000 units and kept entirely in secret. However, it was after World War I, specifically 1921 when a secret cache of Gast guns were found in the Konigsberg fortress, raising the ire of the Allies.
Impressed by the design, the United States test the Gast and vetted its reliability, but never sought to push the design further.