The 321st Missile Squadron is a United States Air Force unit.  It is assigned to the 90th Operations Group, stationed at Francis E. Warren Air Force Base, Wyoming.   The squadron is equipped with the LGM-30G Minuteman III Intercontinental ballistic missile (ICBM).  Their mission is to operate safe and secure nuclear weapons, maintain mission ready facilities, and on order destroy OPLAN assigned targets.
 The squadron was first organized as the 321st Bombardment Squadron at Key Field, Mississippi in April 1942 as a Consolidated B-24 Liberator unit and one of the original squadrons of the 90th Bombardment Group.  The squadron trained with Liberators in the southeastern United States under III Bomber Command until August.
 The squadron moved to Willow Run Airport, Michigan for conversion training on newly manufactured Ford Liberators. Assigned to VII Bomber Command with B-24Ds, the unit moved to Hickam Field, Hawaii in September.  The squadron arrived in northern Queensland, Australia in November 1942 and began bombardment missions under V Bomber Command almost immediately.
 The squadron attacked enemy airfields, troop concentrations, ground installations and shipping in New Guinea, the Bismarck Archipelago, Palau and the southern Philippines. The 321st was awarded a Distinguished Unit Citation for its operations in Papua through January 1943. The unit participated in the Battle of Bismarck Sea in March 1943, and earned another citation for strikes on enemy airfields at Wewak, New Guinea in September 1943 despite heavy flak and fighter opposition.
 During 1944, the 321st supported the New Guinea Campaign through the end of June, then made long-range raids on oil refineries at Balikpapan, Borneo, in September and October.  In January 1945, the squadron moved to the Philippines and supported ground forces on Luzon, attacked industrial targets on Formosa, and bombed railways, airfields, and harbor facilities on the Asiatic mainland.  Shortly before the end of the war in the Pacific, the 90th moved to Okinawa, from which it would be able to strike the Japanese home islands.
 After VJ Day, the squadron flew reconnaissance missions over Japan and ferried Allied prisoners of war from Okinawa to Manila.  It ceased operations by November 1945. The squadron was inactivated in the Philippines in early 1946.
 The squadron was reactivated in July 1947 as a very heavy unit at Andrews Field, Maryland.  It was a component of one of seven bombardment groups activated at Andrews by Strategic Air Command (SAC) that day.  Most of these units, including the 321st, were inactivated by September 1948 and it does not appear they were manned during this period.
 The squadron was again organized at Fairchild Air Force Base, Washington in January 1951 and equipped with the Boeing B-29 Superfortress.  In February, as part of a reorganization of Strategic Air Command wings, the 90th Bombardment Group was reduced to paper status and the squadron was attached to the wing for operational control.  In June 1952, this organization, which was designed to permit the wing commander to focus on the wing's combat units and the maintenance necessary to support combat aircraft, was formalized as the Dual Deputy Organization and the squadron was assigned to the wing.
 In March 1951, the squadron moved to Forbes Air Force Base, where it served primarily as a training unit.  In May, it began serving as an Operational Training Unit for B-29 aircrews and mechanics of newly-activating units.  The squadron help organize and train the 376th, 308th, and 310th Bombardment Wings.
 In June, the squadron added duty as a Replacement Training Unit, primarily providing individual training for aircrew being assigned to existing Far East Air Forces B-29 units during the Korean War. In November 1952 it also began training replacement crews for the RB-29 reconnaissance model of the Superfortress and SHORAN personnel for Strategic Air Command (SAC).  These training activities continued through November 1953.
 The squadron began to fly strategic reconnaissance missions in September 1953. The following year, it replaced its RB-29s with the jet Boeing RB-47 Stratojet, with the first B-47E arriving on 25 June, although crews had begun training in March. One year later, the squadron and the entire 90th Strategic Reconnaissance Wing deployed as a unit to Eielson Air Force Base, Alaska from 5 May until 31 August 1955, where the wing performed the final mapping of Alaska. In May 1958, the 90th Wing returned to the training mission serving as a combat crew training wing for RB-47 aircrews until it was inactivated on 20 June 1960. The squadron's personnel and equipment were transferred to the 45th Bombardment Squadron, which moved to Forbes on paper from Schilling Air Force Base, Kansas the same day.
 The squadron was reactivated on 9 April 1964 as an intercontinental ballistic missile squadron assigned to the 90th Strategic Missile Wing at Francis E. Warren Air Force Base, Wyoming, and equipped with fifty LGM-30B Minuteman Is, armed with a single reentry vehicle.  The squadron was the third of the 90th Wing's four Minuteman squadrons to activate, as construction on launch facilities continued until the middle of 1964.  Beginning in June 1973, its Minuteman I missiles began to be replaced by LGM-30G Minuteman IIIs, which could carry up to three reentry vehicles. In 2001 in compliance with the Strategic Arms Reduction Treaty, these missiles were limited to a single reentry vehicle
 The squadron won the Samuel C. Phillips Award as the best missile squadron in Air Force Space Command in 2005, 2010 and 2019.
 Download coordinates as:
 41°07′59″N 104°52′01″W﻿ / ﻿41.13306°N 104.86694°W﻿ / 41.13306; -104.86694﻿ (Francis E. Warren AFB)
  This article incorporates public domain material from the Air Force Historical Research Agency.