Armor-Plate, the metallic sheathing of a ship-of-war or of a fortification, used as a protection against artillery fire. It is claimed that John Stevens at Hoboken, New Jersey, was the first to suggest the use of armor, but the first practical use was in 1855 by the French on their ships-of-war. Armor-plate manufacture has gone through several stages. The first plates were made of wrought iron, but the invention of rifled cannon made it possible to pierce any single thickness of wrought iron that could be then made. In 1873 C. Cammell & Co. invented the compound plate, which was prepared by pouring liquid steel on to hot iron plates. Then Schneider & Co., of Creusot, France, demonstrated that steel plates are preferable. About 1890 experiments made by the United States government at Annapolis showed that a plate made of an alloy of steel and nickel is far superior to the simple steel. More recently, the resisting power of steel armor-plate had been increased 25 per cent, by the process invented by Harvey, an American. This consists in face-hardening the plates, by causing the outer layers of the metal to take up a greater percentage of carbon. The Krupp firm of Essen, Germany, discovered a new process, which is kept secret, for hardening both steel and nick-steel plates, by which a product of unexcelled quality is turned out. Its resistance is 20 per cent greater than that of harveyized steel. One foot of the best armor made to-day has more endurance than two feet of the best armor in 1880. It is said that the principal armor-plate makers of America, England and France are now using this process, under agreement with Krupp. The steel is subjected, while hot, to hydraulic forging. This renders the whole mass more homogeneous than old methods, making it stronger and freer from flaws. It is next sawed or planed into plates of the required size, and then harveyized by cementation, hardening and tempering. Krupp’s process carries the hardening deeper into the plate, because chrome, probably, as well as nickel is used in the steel. Hardening the steel increases the brittleness and the liability of the plate to crack, but its back remains extremely though, and so the risk of cracking is lessened. Krupp plates resist ordinary projectiles better than Harvey armor does, but Harvey plates resist capped projectiles better and not are liable to crack. Krupp armor 12 inches thick withstands and smashes 12-inch shells, though dented four or six inches, but is cracked by 1,800-lb. torpedo shells. On May 27, 1908, the 11-inch armor plate of the Florida, a United States monitor, successfully resisted 12-inch shells containing a new high explosive. The first plates used were less than five inches thick. By 1876 solid steel plates of 22-inch thickness had been produced. Fully 4,000 tons of armor-plate are used on the exposed sides and turrets of some modern battleships.