a German aircraft with a machine gun for the first time and the era of air combat was underway as more and more aircraft were fitted with machine guns. Evolution of fighter aircraft The pusher solution As early as 1912, designers at the British firm Vickers were experimenting with machine gun carrying aircraft. The first concrete result was the Vickers Experimental Fighting Biplane 1, which featured at the 1913 Aero Show in London. and appeared in developed form as the FB.5 in February 1915. This pioneering fighter, like the Royal Aircraft Factory F.E.2b and the Airco DH.1, was a pusher type. These had the engine and propeller behind the pilot, facing backward, rather than at the front of the aircraft, as in a tractor configuration design. This provided an optimal machine gun position, from which the gun could be fired directly forward without an obstructing propeller, and reloaded and cleared in flight. An important drawback was that pusher designs tended to have an inferior performance to tractor types with the same engine power because of the extra drag created by the struts and rigging necessary to carry the tail unit. The F.E.2d, a more powerful version of the F.E.2b, remained a formidable opponent well into 1917, when pusher fighters were already obsolete. They were simply too slow to catch their quarry. Machine gun synchronisation The forward firing gun of a pusher "gun carrier" provided some offensive capability—the mounting of a machine gun firing to the rear from a two-seater tractor aircraft gave defensive capability. There was an obvious need for some means to fire a machine gun forward from a tractor aircraft, especially from one of the small, light, "scout" aircraft, adapted from pre-war racers, that were to perform most air combat duties for the rest of the war. It would seem most natural to place the gun between the pilot and the propeller, firing in the direct line of flight so that the gun could be aimed by "aiming the aircraft". It was also important that the breech of the weapon be readily accessible to the pilot so that he could clear the jams and stoppages to which early machine guns were prone. However, this presented an obvious problem: a percentage of bullets fired "free" through a revolving propeller will strike the blades, with predictably destructive results. Early experiments with synchronised machine guns had been carried out in several