The X-14 first flew on 19 February 1957 as a vertical takeoff, hover, then vertical landing. The first transition from hover to horizontal flight occurred on 24 May 1958. In 1959, its Viper engines were replaced with General Electric J85 engines. That year the aircraft was delivered to the NASA Ames Research Center as the X-14A. During the development of the P.1127, Hawker test pilots Bill Bedford and Hugh Merewether visited NASA Ames to fly the X-14 and acquaint themselves with jet V/STOL aircraft handling prior to the first flights of the prototype P.1127. It served as a test aircraft with NASA until 1981.