The first cannon were clumsy and comparatively inefficient. They were made of wooden bars held together with iron hoops, and they shot balls of stone. Cannon of bronze were next made, and in the latter part of the fifteenth century iron cannon came into use. The next improvement was the production of cannon of steel, and for some years past the best artillery has been made of this material. After stone balls ceased to be used, round balls of iron were utilized. These in time gave way to cylindrical projectiles of steel. Originally cannon were loaded at the muzzle, but in recent years breech-loading devices have been developed, so that now all of the best modern guns are loaded from the rear.
Within the last twenty-five years, rapid-fire guns have been developed. These have a mechanism by which the breech is opened and closed again by a single motion of a lever. The loading with projectile and powder is also done with one motion. The rapidity of firing varies from two hundred shots per minute in the smallest guns to one shot in two minutes in the largest. The largest British cannon are nearly eighteen inches in calibre (diameter of bore), weigh a hundred tons, are thirty-five feet long, shoot a shell weighing nearly a ton, consume at each charge 450 pounds of powder, and have the power of penetrating solid iron armor plate to the depth of almost two feet, at a distance of one thousand yards. At least a year and a quarter is required for making one of the great, heavy guns, and often a longer time. The cost of constructing one of the largest English cannon is about $117,000, and it costs about $175 to fire the gun once. Some of the most powerful cannon may be relied upon to hit an object ten feet high at a distance of about nine thousand yards. In battle, however, owing to conditions of atmosphere and the limitations of human vision, fire would rarely be opened at a greater distance than three thousand yards, or not quite two miles.
Guns discharged by machinery have been introduced within the last half-century. The fire from machine guns is practically continuous. Several kinds have been invented and improved by various persons. One of the best types of this kind of ordnance is the Gatling gun, invented in 1860 by Dr. R. J. Gatling, of Indianapolis. It consists of a number of parallel barrels, usually ten, grouped around and fastened to a central shaft. Each barrel has its own mechanism for firing. As the barrels revolve, loaded cartridges are fed into them by machinery and the empty cartridges are ejected. By means of an automatic mechanism, the bullets may be scattered over such an arc in front as may be desired, or concentrated upon a narrower range. The Gatling gun can fire at the rate of 1200 shots per minute; it literally hails bullets.