A cannon is an artillery piece consisting of a metal tube, used to aim and fire missiles propelled by the explosion of gunpowder in the closed end of the cylinder. Cannon, first used in the fourteenth century, were originally made of bronze or iron. Major improvements in the 19th century included the introduction of steel barrels, more powerful chemical propellants, breech-loading mechanisms, and standardized parts. By World War I recoil devices were employed to absorb the shock of firing.