It served as the standard-issue sidearm for the United States Armed Forces from 1911 to 1986. It was widely used in World War I, World War II, the Korean War, and the Vietnam War. The pistol's formal designation as of 1940 was Auto Pistol, Caliber .45, M1911 for the original model of 1911 or Auto Pistol, Caliber .45, M1911A1 for the