Aircraft-mounted machine guns were first used in combat in World War I. Immediately this raised a fundamental problem. The most effective position for guns in a single-seater fighter was clearly, for the purpose of aiming, directly in front of the pilot; but this placement would obviously result in bullets striking the moving propeller. Early solutions, aside from simply hoping that luck was on the pilot's side with an unsynchronized forward-firing gun, involved either aircraft with pusher props like the Vickers F.B.5, Royal Aircraft Factory F.E.2 and Airco DH.2, wing mounts like that of the Nieuport 10 and Nieuport 11 which avoided the propeller entirely, or armored propeller blades such as those mounted on the Morane-Saulnier L which would allow the propeller to deflect unsynchronized gunfire. By mid 1915, the introduction of a reliable gun synchronizer by the Imperial German Flying Corps made it possible to fire a closed-bolt machine gun forward through a spinning propeller by timing the firing of the gun to miss the blades. The Allies had no equivalent system until 1916 and their aircraft suffered badly as a result, a period known as the Fokker Scourge, after the Fokker Eindecker, the first German plane to incorporate the new technology.