Davis–Monthan Air Force Base is a United States Air Force base 5 miles (8.0 km) south-southeast of downtown Tucson, Arizona. The host unit for Davis–Monthan AFB is the 355th Wing (355 WG) assigned to Twelfth Air Force (12AF), part of Air Combat Command (ACC). The base is best known as the location of the Air Force Material Command's 309th Aerospace Maintenance and Regeneration Group (309 AMARG), the aircraft boneyard for all excess military and U.S. government aircraft and aerospace vehicles. Davis–Monthan Air Force Base is a key ACC installation. The 355th Wing (355 WG) provides A-10 Thunderbolt II close air support and OA-10 forward air controllers to ground forces worldwide. The 355 FW is also the sole formal training unit for the A-10 aircraft, providing initial and recurrent training to all U.S. Air Force A-10 and OA-10 pilots, to include those in the Air Force Reserve Command (AFRC) and the Air National Guard (ANG)