Nellis Air Force Base is a United States Air Force installation located in southern Nevada, within the Las Vegas Valley. Constructed in 1941 as Las Vegas Army Airfield, it has been continuously operational since its activation on December 20, 1941. The base was renamed Las Vegas Air Force Base in 1948 and subsequently Nellis Air Force Base on April 30, 1950. It covers approximately 4,600 hectares (11,300 acres) and is owned by the Department of Defense, operated by the United States Air Force under Air Combat Command (ACC). Nellis AFB is known as the Air Force's center for advanced combat training, hosting air combat exercises such as Exercise Red Flag and close air support exercises like Green Flag-West, which utilize the nearby Nevada Test and Training Range (NTTR). The main unit stationed at Nellis is the USAF Warfare Center, which coordinates training for composite strike forces involving various USAF aircraft types, as well as units from the US Army, US Navy, US Marines, NATO, and allied nations. The base is also home to the 99th Air Base Wing (Host), 57th Wing, and the United States Air Force Thunderbirds air demonstration squadron, which moved to Nellis in 1956. The base features two concrete runways: 03L/21R, measuring 3,084.5 meters, and 03R/21L, measuring 3,063.5 meters. Nellis AFB employs approximately 9,500 military and civilian personnel and supports operations at Creech Air Force Base, Tonopah Test Range, and the Nevada National Security Site.