Airplanes had been around for just a decade when WWI started, and while they had obvious potential for combat applications as an aerial platform for bombs and machine guns, it wasn’t quite clear how the latter would work, since the propeller blades got in the way. In the first attempt, the U.S. Army basically tied the gun to the plane (pointing towards the ground) with a leather strap, and it was operated by a gunner who sat beside the pilot. This was not ideal for aerial combat and inconvenient because it required two airmen to operate. Another solution was mounting the gun well above the pilot, so the bullets cleared the propeller blades, but this made it hard to aim. After the Swiss engineer Franz Schneider patented his idea for an interrupter gear in 1913, a finished version was presented by Dutch designer Anthony Fokker, whose “synchronizer,” centered on a cam attached to the propeller shaft, allowed a machine gun to fire between the blades of a spinning propeller. The Germans adopted Fokker’s invention in May 1915, and the Allies soon produced their own versions. Schneider later sued Fokker for patent infringement.