The 864th Aviation Battalion was activated in December 1942 at Camp Geiger, Washington near Spokane. The Battalion served in the Pacific Theater during World War II, earning three campaign streamers for New Guinea, the Bismarck Archipelago, and Luzon. The unit also earned the Philippine Presidential Unit Citation. The unit was deactivated in Japan on 30 June 1946. The army allotted the battalion to the organized Reserves and activated it at Morristown, New Jersey on 14 March 1949. The unit was deactivated the following September. In March 1951, the Army reactivated the battalion at Tulsa, Oklahoma, only to inactivate it a year later. In 1955 the battalion was withdrawn from the Army Reserve and allotted to the Regular Army. The 864th was reactivated at Wolters Air Force Base, Texas on 25 September 1955. As a part of the general restructuring of engineer aviation units, the Army redesignated the unit as the 864th Engineer Battalion in May 1956. In May 1965, the battalion was shipped to Cam Ranh Bay, South Vietnam.