USAF Guide to Aviation Safety Investigation - Paperbackby U. S. Air Force (Created by) The United States Air Force (USAF) is the aerial warfare service branch of the United States Armed Forces. The USAF was initially a part of the U. S. Army, but was formed as a separate branch of the military in 1947 under the National Security Act. Although it is the most recent branch of the U. S. Military to be formed, the USAF is the most technologically advanced air force in the world. The Air Force e Publishing