The long gun of modern days is of necessity breech-loading. The development of other elements gave, as a resultant, great length; and this, in turn, required a system of charging which would permit protection for the men while loading, and would obviate the intolerable inconvenience of ramming home powder and shot in a long muzzle-loader—an operation which was, in fact, impossible beyond a certain limit of length. The advocates of the older construction, especially in England, urged long and earnestly its simplicity and the superior strength of a solid breech; but the logic of events was against them, and the breech-loader won a complete triumph. It is worthy of note that it, like rifling and the principle of building up, was but a revival. From the warship Mary Rose, sunk in 1545 in action off Spithead, there were recovered in 1836 a number of guns, some of which are of wrought iron, built-up and breech-loading. There are in use two methods of closing the breech when the gun is loaded from the rear. In French, English, and American ordnance an axial screw-plug is inserted; in the Krupp system a cylindro-prismatic breech-block slides in a horizontal opening cut across the bore. The former, or interrupted screw mechanism, was first set forth in the United States’ patent of 1849 to Chambers. In projectiles the tendency of the modern era has been towards simplification. Bar-shot, chain-shot, and grape have disappeared, while canister and solid shot are becoming obsolete. There remain shrapnel as the “man-killer” of this age, and explosive shell, differentiated into armor-piercing and that for attack on unarmored structures. Lieutenant Shrapnel, in 1796, invented the projectile which bears his name. In its modern form, it consists of a steel case containing lead or iron balls and a light bursting charge of powder, ignited by a time-fuse carried in the head. This projectile is most formidable against bodies of men, boats, and the embrasures of forts, since, when it is ruptured, the balls are dispersed, covering a wide area.