The 519th Fighter-Interceptor Squadron is an inactive United States Air Force unit. Its last assignment was with the 521st Air Defense Group at Sioux City Municipal Airport, Iowa, where it was inactivated on 18 August 1955. The squadron was first activated during World War II as the 637th Bombardment Squadron, a dive bomber unit, but was disbanded before participating in combat in a general reorganization of Army Air Forces training units. It was reconstituted during the Cold War as a fighter interceptor unit supporting the air defense of the United States. History World War II The squadron was activated in April 1943 as the 637th Bombardment Squadron at Key Field, Mississippi, as one of the original squadrons of the 408th Bombardment Group. In August, along with other Army Air Forces (AAF) single engine dive bomber units, it became a fighter-bomber unit as the 519th Fighter-Bomber Squadron. The squadron did not receive aircraft to begin training until October, after it had moved to Drew Field, Florida. It served as an operational training unit with various aircraft, providing cadres to "satellite groups" and as a replacement training unit, training individual pilots. However, the AAF was finding that standard military units, based on relatively inflexible tables of organization, were not proving well adapted to the training mission. Accordingly, it adopted a more functional system in which each AAF base was organized into a separate numbered unit. In this reorganization the squadron was disbanded in 1944 as the AAF converted to the AAF Base Unit system. It was replaced, along with other units at Woodward Army Air Field, by the 267th AAF Base Unit (Combat Crew Training Station, Fighter) in a reorganization of the AAF in which all units not programmed for deployment overseas were replaced by AAF Base Units to free up manpower for assignment overseas. Cold War air defense During the Cold War the squadron was reconstituted, redesignated as the 519th Fighter-Interceptor Squadron and activated at Sioux City Municipal Airport, Iowa in December 1954, where it was assigned to the 521st Air Defense Group. The squadron replaced the 87th Fighter-Interceptor Squadron, which moved to England from Sioux City. At Sioux City, the squadron flew airborne intercept radar equipped and Mighty Mouse rocket armed North American F-86D Sabre aircraft. The 521st Group was inactivated and replaced by the 53d Fighter Group (Air Defense) in 1955 as part of Air Defense Command's Project Arrow,