Lineage. Constituted as Air Base Squadron, 22 Air Base Group, on 20 Nov 1940. Activated on 15 Jan 1941. Redesignated: 21 Air Base Squadron on 17 Jan 1941; 21 Base Headquarters and Air Base Squadron on 13 Jan 1942. Disbanded on 1 Apr 1944. Reconstituted, and redesignated 21 Mission Support Squadron,