Two X-31 Enhanced Fighter Maneuverability (EFM) demonstrators flew at the NASA Dryden Flight Research Center to obtain
data that may apply to the design of highly maneuverable next-generation fighters. The program ended in June 1995.

A second program dubbed VECTOR ran 1999-2003 to investigate automatic landings at high angle of attack.
Aircraft #2 made its first flight on January 19, 1991, with DASA chief test pilot Dietrich Seeck at the controls.