The F-102 Delta Dagger fighter aircraft was part of the backbone of the United States air defenses in the late 1950s. Entering service in 1956, its main purpose was to intercept invading Soviet bomber fleets. However the project was troubled and by the early 1960s the plane was being replaced by F-101 Voodoos and F-4 Phantom IIs. Many of the F-102s were transferred to United States Air National Guard[?] duty by the mid- to late-1960s and the plane left service altogther in 1976.