The M1911, also known as the Colt 1911, or the Colt Government, is a single-action, semi-automatic, magazine-fed, recoil-operated pistol chambered for the .45 ACP cartridge. The pistol's formal designation as of 194 was Automatic Pistol, Caliber .45, M1911 for the original model of 1911 or Automatic Pistol, Caliber .45, M1911A1 for the M1911A1, which was adopted in 1924. The designation changed to Pistol, Caliber .45, Automatic, M1911A1 in the Vietnam War era.
Designed by John Browning, the M1911 is the best-known of his designs to use the short recoil principle in its basic design. The pistol was widely copied, and this operating system rose to become the preeminent type of the 2th century and of nearly all modern centerfire pistols. It is popular with civilian shooters in competitive events such as USPSA, IDPA, International Practical Shooting Confederation, and bullseye shooting. Compact variants are popular civilian concealed carry weapons in the U.S. because of the design's relatively slim width and the stopping power of the .45 ACP cartridge.
The U.S. military procured around 2.7 million M1911 and M1911A1 pistols during its service life. The pistol served as the standard-issue sidearm for the United States Armed Forces from 1911 to 1985. It was widely used in World War I, World War II, the Korean War, and the Vietnam War. The M1911A1 was replaced by the adoption of the 9 mm Beretta M9 pistol as the standard U.S. military sidearm in 1985. However, the U.S. Army did not replace the M1911A1 with the Beretta M9 until October 1986, and due to the M1911's popularity among users has not been completely phased out. Modernized derivative variants of the M1911 are still in use by some units of the U.S. Army Special Forces, U.S. Marine Corps and the U.S. Navy.