High Quality Content by WIKIPEDIA articles! The XII Bomber Command is an inactive United States Air Force unit. Its last assignment was with the Twelfth Air Force, based in Corsica, France. It was inactivated on 10 Jun 1944. The United States Air Force (USAF) is the aerial warfare, space warfare, and cyberwarfare branch of the U.S. armed forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on 18 September 1947 under the National Security Act of 1947.