Davis–Monthan Air Force Base is a United States Air Force base 5 miles southeast of downtown Tucson, Arizona. It was established in 1925 as Davis–Monthan Landing Field. The host unit for Davis–Monthan AFB is the 355th Wing assigned to Twelfth Air Force (12AF), part of Air Combat Command (ACC). The base is best known as the location of the Air Force Materiel Command's 309th Aerospace Maintenance and Regeneration Group, the aircraft boneyard for all excess military and U.S. government aircraft and aerospace vehicles.