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. It was widely used in World War I, World War II, and the Korean War. The pistol's formal designation as of 1940 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.