Description 4th USAAF The 4th USAAF was originally constituted as the Southwest Air District on October 19, 1940, and activated on December 18, 1940. It was redesignated as the 4th Air Force in early 1941. Initially, the 4th Air Force provided air defense for the western United States until 1943 while also training new units. 4th Air Force Constituted as Southwest Air District on October 19, 1940. Activated on December 18, 1940. Redesignated as the 4th Air Force in early 1941. Provided air defense for the western U.S. until 1943 and simultaneously trained new organizations. Later focused primarily on training replacements for combat units. Assigned to the Air Defense Command in March 1946. Assigned to Continental Air Command in December 1948, focusing on air defense until 1949 and subsequently on reserve and National Guard activities.
