321st may refer to: * 321st Air Expeditionary Group (321 AEG), a provisional United States Air Force Air Combat Command unit * 321st Air Expeditionary Wing, a United States Air Force unit assigned United States Air Forces Central (USAFCENT) * 321st Air Refueling Squadron, an inactive United States Air Force unit * 321st Division (Imperial Japanese Army), active 23 May 1945–1945 * 321st Engineer Battalion (United States), Army Reserve battalion during World War II and Operation Iraqi Freedom * 321st Field Artillery Regiment (FAR), a field artillery regiment of the United States Army * 1st Battalion, 321st Field Artillery Regiment (1-321 FAR), an inactive field artillery battalion of the United States Army * 2nd Battalion, 321st Field Artillery Regiment (2-321 FAR), an inactive field