When the U.S. entered World War I, the semiautomatic M1911 Pistol was the standard military sidearm. The Army asked manufacturers to produce revolvers that could fire the .45 ACP ammo used in the M1911. Smith & Wesson based their M1917 on their Second Model .44 Hand Ejector Revolver. They patented half-moon clips to hold the rimless .45 ACP ammo securely and eject empty cartridges from the cylinder. The Army persuaded Smith & Wesson to allow Colt and others to use the half-moon clips due to the wartime emergency.