The YF-107A was originally designed as a tactical fighter-bomber version of the F-100, and was entered into a competition sponsored by the Air Force. Originally designated the F-100B, the aircraft featured a recessed weapons bay under the fuselage, as well as an all-moving vertical fin and a control system which permitted the plane to roll at supersonic speeds. The aircraft's most distinguishing feature is its Variable Area Inlet Duct, mounted in an unconventional position directly above and just behind the cockpit, which automatically controlled the amount of air fed to the jet engine. The air intake was located overhead and behind to prevent it from interfering with the aircraft's weapon's control and guidance radar. Extensive design changes resulted in its redesignation from F-100B to YF-107A before the first prototype flew.