The M1911 is a single-action, semiautomatic handgun chambered for the .45 ACP cartridge. It was designed by John M. Browning, and was the standard-issue side arm 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. Its 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, adopted in 1924. The designation changed to Pistol, Caliber .45, Automatic, M1911A1 in the Vietnam era. In total, the United States procured around 2.7 million M1911 and M1911A1 pistols during its service life.

The same basic design has also been offered commercially and has been used by other militaries. In addition to the .45 ACP (Automatic Colt Pistol), models chambered for .38 Super, 9 mm Parabellum, .400 Corbon, and other cartridges were also offered. The M1911 was developed from earlier Colt designs firing rounds such as .38 ACP. The design beat out many other contenders during the government's selection period, during the late 1890s and 1900s, up to the pistol's adoption. The M1911 officially replaced a range of revolvers and pistols across branches of the U.S. armed forces, though a number of other designs would see some use in certain niches.

The M1911 is the most well-known of John Browning's designs to use the short recoil principle in its basic design. Besides the pistol being widely copied itself, this operating system rose to become the pre-eminent type of the 20th century and of nearly all modern pistols. Source: Wikipedia.org