ARMOR PLATES, slabs of metal with which the sides of war vessels are cov ered for the purpose of rendering them shot-proof. The idea of using slabs of iron or steel for protection against mis siles is not a recent invention. The first attempt to use armor-plate on the sides of ships was made by John Stevens, of Hoboken, in 1812. He built a vessel shaped somewhat similar to the later vessels of the "Monitor" type, and sheathed it along the water line with laminated iron plates. His vessel was offered to the United States Government but was not accepted. The French were the first to adopt armor-plating. In 1854 they sent floating batteries to the Black Sea, sheathed with 4% inches of lami nated iron, which was proof against the fire of the 68-pounders, then the most powerful guns. The British admiralty, following this example, sent out very slow and unmanageable iron-clad batter ies in 1855-1856. These batteries pro tected the ships very well against round balls from the unrifled cannon of the day. It was not, however, till the Ameri can Civil War that armor-plating came into general use. The Confederate ram "Merrimac" was the first practical ar mor-plated vessel in the United States, her sheathing consisting of railroad Her successful opponent, the "Monitor," was heavily sheathed with laminated iron plates extending several feet be low the water line.
Harvey introduced the process of car bonizing the face of armor-plate, great ly increasing its hardness. The plate,
having been placed in a furnace, is cov ered with a layer of carbonizing mate rial about a foot thick, over which is laid a covering of brick to exclude the flame and air from the carbonizing mate rial. The doors of the furnace are bricked up and a high heat maintained for about 100 hours. The plate is re moved and its surface cleared when cold, it is then reheated, and sprayed with cold water, producing an exceedingly hard surface. This Harveyized steel was used for nearly all the American and foreign men-of-war, until, in 1895, a process was discovered at the iron works of Krupp, at Essen, by which the face of the plate was made so hard that it cut glass like a diamond, while the back remained so tough that it would suffer no injury from cracks when struck by a projectile. The Krupp process is somewhat similar to, and an improvement on, the Harvey process.
A Harveyized plate has been pierced to a depth of 14 inches by a 6-inch soft capped projectile, so that the cap showed on the back. The Krupp armor is per forated, but not cracked, by a projectile with a velocity exceeding 2,500 feet per second. The Harvey plate is cracked but rarely perforated at a velocity of less than 2,000 feet per second. The projec tiles used for testing purposes vary from 100 pounds to 850 pounds in weight.