Thunderbolts thereafter. In early 1943, the group added a fourth squadron, the 438th Fighter Squadron. The AAF found that standard military units, based on relatively inflexible tables of organization were proving less well adapted to the training mission. Accordingly, a more functional system was adopted in which each base was organized into a separate numbered unit. The group was disbanded in as a result of this reorganization in 1944 and its personnel, equipment and mission were assumed by the 338th AAF Base Unit (Replacement Training Unit, Fighter). Cold War Air Defense The group was reconstituted, redesignated as the 53d Fighter Group (Air Defense) and activated to replace the 521st Air Defense Group at Sioux City Municipal Airport as part of Air Defense Command's Project Arrow to bring back on the active list fighter units that had achieved memorable records in the two World Wars. The 14th Fighter-Interceptor Squadron (FIS), already at Sioux City transferred from the 521st, while the 13th FIS moved to Sioux City to replace the 519th FIS. Both squadrons flew rocket armed and radar equipped F-86D Sabres. Between August 1955 and April 1960 the 53d served as an air defense unit, participating in North American Air Defense Command (NORAD) exercises and testing automated air defense systems. It also was the host organization for the USAF and was assigned several support units to carry out this function. In the fall of 1957 both of the group's squadrons upgraded their Sabres to F-86L models with data link for interception control through the Semi-Automatic Ground Environment system. In July 1959 the 13th FIS moved to Glasgow AFB, Montana and was reassigned. The group and its remaining components were inactivated in 1960. In 1985, the group was redesignated as the 53d Tactical Fighter Group, but it was never active under that designation. Test and Evaluation The USAF Tactical Air Warfare Center was activated in 1963 to improve use of USAF tactical aviation in support of ground forces by operationally testing weapon systems and tactics for the joint U.S. Strike Command. It employed a cross-section of tactical aircraft from Tactical Air Command (TAC) bases across the country. During the Vietnam War it tested tactical weapons systems and tactics for use in Southeast Asia. After the war it continued operational testing of new tactical aviation weapon systems. In 1977 the center began an annual series of Air Force-wide exercises to improve command, control,