The Germans showed the deflector plates to Anthony Fokker, a Dutch designer who was building airplanes in Germany. He quickly saw the drawbacks to the deflector plates, and he and his engineers soon developed an interrupter gear solution that worked. The gun would only fire when the spinning propeller was not in the line of fire. This photo shows an early mounting of a machine gun to a Fokker aircraft. The butt stock and pistol grip on the machine gun make it clear that this is a hasty adaptation of an infantry gun to the airplane, but the open slots in the cooling jacket around the gun barrel are clearly designed for aircraft use. The infantry version of this gun had a water filled cooling jacket. (Wikimedia Commons https://commons.wikimedia.org/wiki/File:Fokker_M.5K-MG_(21251693859).jpg)