It can trace its roots back to the "21st Pursuit Squadron", which was activated on 1 February 1940 at Moffett Field, California. It took part in the combat in the Philippine Islands, from 8 December 1941. Being inactivated on 2 April 1946, later being activated as the "21st Helicopter Squadron", and inactivated again. Then activated for the Vietnam war on 30 June 1967, assigned to Tactical Air Command, later being redesignated the "21st Special Operations Squadron" on 1 August 1968. The squadron took part in both Operation Frequent Wind, and the Mayaguez incident. In addition to its combat duties, the unit has taken part in a number of humanitarian aid operations.