Lineage. Constituted as 321 Bombardment Squadron (Heavy) on 28 Jan 1942. Activated on 15 Apr 1942. Redesignated as 321 Bombardment Squadron, Heavy, on 6 Mar 1944. Inactivated on 27 Jan 1946. Redesignated as 321 Bombardment Squadron, Very Heavy, on 11 Jun 1947. Activated on 1 Jul 1947.