High Quality Content by WIKIPEDIA articles! The North American XF-108 Rapier was a proposed long-range, high-speed interceptor aircraft designed by North American Aviation. Initiated to defend the United States from supersonic Soviet bombers, the program, initially called NA-257, was cancelled in 1959 due to a shortage of funds and the Soviet adoption of ballistic missiles as their primary means of nuclear attack. Only one mock-up was constructed. Had it flown, it would have been the heaviest fighter of its era, surpassing the Soviet Tupolev Tu-128.