Designed 1949 with goal to perfect F-86 design and, with significantly more powerful engine, make supersonic. First production aircraft to go supersonic in straight and level flight. Production of 2 prototypes authorized; built 203 of first production series (A model). Operational use delayed by series of accidents 1954 which led to suspension of program and modifications to structure and surfaces of wing and tail. Second series, C, fighter-bomber; first flight 17 Jan 55. Third version, D, first flew 24 Jan 56 with considerable changes to structure and avionics; air- to-air/air-to-ground missiles added to weaponry. Last version, 2-seat F operational trainer, first flew 3 Aug 56. F-100 used extensively in Vietnam.