In the Wilson process & Co.), molten steel is poured on a white-hot iron plate, this adding one-third to the thickness of the plate, which is afterwards rolled. In the Ellis process (Brown & Co.) a wrought - and a rather thin, hard steel plate are separately made. The lower plate is placed in the furnace; iron bars arc placed around the edge forming a berm, and the steel plate laid on the bars. After they are raised to a welding heat, molten steel is poured into the space between the plates, welding all together. There are other systems of com pound plate manufacture, but these have at tained the greatest eminence, if extent of use is a criterion, and they exemplify the type. The first really successful compound plates appeared in 1877, and from that date they competed with steel plates on apparently-equal terms until 1889, when Schneider brought out his first nickel-steel plate. The trial of this plate took place in but it was not until the next year that attention was fully drawn to the importance of the new metal. The United States naval authorities, having purchased in Europe a compound plate from Calomel] & a steel plate and also one of nickel steel from Schneider et Cie., held a competitive test at the naval proving-ground, Annapolis, in September, 1890. The compound plate was ignominiously defeated, both by the steel plate and by that of nickel steel. Indeed, the defeat was so complete and convincing that it stopped the mannfacture of compound plates at once. The Navy Department had already corn itself to the manufacture of steel armor, and large contracts for it had been given out sonic Years before. The wisdom of the decision in fat.or of steel had been questioned in Con gress and in the public press, and the trial was instituted to convince the doubters; the occa sion also served to effect a trial of a nickel-steel plate which had been acquired on account of the promising results obtained by Messrs. Schnei der et Cie the year before. The important re sults of this trial had hardly appeared when a second trial of like revolutionary character took place. A year or two before, Air. Harvey, a manufacturer of fine-grade tool steel, was at the Washington gun factory. In a conversation with him, Captain Folger, the superintendent of the naval gun factory, suggested the attempt to adapt the Harvey system of hardening tool steel to armor plate. After considering the matter, Mr. Harvey decided to make some experi ments looking to surface hardening armor; and the result was the Harvey process of surface carburization- and hardening. In this process the plate is placed on the floor of a suitable furnace in a bed of refractory mate rial, leaving the surface to be hardened upper most. This is covered with carbonaceous mate rial, which is rammed clown upon it; over the carbon is put a layer of sand covered in with fire-brick. The temperature of the furnace is then raised to about the temperature of melting cast iron and kept so for several days, until the required additional carborization—usually about 1 per cent.—is effected. The plate is then removed, and, when cooled to a dull cherry red, is hardened by a water jet or immersion in run ning water. The trial of the first plate made by the Harvey process took place February 14, 1891, and was very successful. The popularity of the new armor was immediate, and the muse is not far to seek, for in its construction it embodied the combined views of armor theorists.
Supporters of compound armor accepted the defeat of the year before with reservations. They still adhered to the idea of a hard face and soft back ; and they were right in so doing. The ad vocates of a single. practically homogeneous plate were also satisfied ; they held. very properly, that. the strength of iron armor plate most not lie solely in defeating the projectile by breaking it up, lint in keeping it out by the toughness of the plate. A third class of critics—more or less in sympathy with the compound armor people, but not cmpletcly so, and declaring that no armor is tit to put on a ship which breaks up under attack and leaves the side bare after wards, even if it stops that particular projectile, —were also satisfied. In England, the Harvey system was adopted almost at once, but notions of misplaced economy and the difficulty of work ing the resulting metal caused the rejection of nickel in steel. lint this view was held only a few years. The next improvement, in 1895, was effected by the Carnegie Company, which found that a reforging of plates after carburizing con siderably improved the quality. Soon after the
appearance of Harveyized armor, Krupp, Schnei der, the Terni Works, and several other Euro pean makers began experiments along the same lines. The ones mentioned alone produced any noteworthy results, and it is to be remarked that all three adopted the method of carburization by means of gas rich in carbon. Of these three kinds, the product of Krupp is generally re garded as the best. Krupp armor differs from that previously made, not only in the process of manufacture, but in its chemical constitution. Its exact character is a jealously guarded trade secret. which has been sold at a high price to nearly all the great armor manufacturers of the world, but that it contains a small amount of chromium as well as carbon is now generally understood. Previous attempts to produce chrome steel armor had not been successful, though the trials had been numerous and per sistent. Nearly all of the armor now applied to ships, except very thin plates, is made by the Krupp process. The Terni Works in Italy. and Schneider in Frame, have continued the devel opment of their own processes, which give nearly equal results.
The object of having a hard face to armor is to break up projectiles by shock, or so to strain or deform them as to reduce their penetration. It is particularly effective on oblique impact i.e. where the projectile strikes at an angle with the plate). To combine hardness with toughness was the aim of armor makers for a quarter of a century, and success was not ob tained until the advent of nickel steel. Ilad not the improvement of projectiles and gtms kept pace with the development of armor. ships could now be made invulnerable; but both have improved so that the relation of guns and armor is now less favorable to the latter than at almost any time in its history. Nevertheless, armor is absolutely indispensable to the protection of ships and their crews against all classes of gun fire. The power of good Harvey nickel-sleel ar mor to resist penetration is about equal to that of double the thickness of wrought iron, and the resisting power of Krupp armor is 10 to 15 per cent. greater. These figures arc for attack by ordinary armor-piercing projectiles. Pro jectiles of this type which are fitted with soft caps (see PROJECTILES) penetrate about as deeply in Krupp as in Ilarvey armor, and the gain by the of caps is equal to a reduction in thickness of S to 10 per cent. in Harvey armor and 15 to 20 in Krupp—that is to say. a capped projectile will perforate a Harvey plate 8 to 10 per cent. thicker, or a Krupp plate 15 to 20 per cent. thicker, than will a projectile not provided with a cap. The penetration in armor of the latest United States guns is seen in the aceompanying table: The principal armor makers in the United States are the Carnegie Works at Pittsburg and the Bethlehem Steel Company of South Bethle hem. Other companies have furnished thin plates.
Another form of armor, not used for ships, but only fur fortifications, is made of chilled cast. iron, and was developed by Gruson, whose works were located at Magdeburg-Duckau. Herr Gruson died in 1893. and his establishment was then purchased by Krupp. The metal was a specially excellent low carbon east iron. chilled in the casting on its outer surface, without ap parently weakening its tenacity. It is designed and shaped to be used in cupolas of special dome like form covering one or more guns. Where weight is of no importance it is a very effective defense. Works for its manufacture in the United States have been established near Phila delphia.
A full account of the early development of armor by Lieut. E. W. Very, U. S. N., is found in the United States Naval Institute, vol. ix., No. 3 (1883). Numerous other papers of less length. but of much value, appear in later num bers of the Proceedings. For additional informa tion, see Armor and Its Attack by Artillery, Lon don, 1887, by C. Orde Drown; also, the Annual of the Office of Naral Intelligence, U. S. Navy, especially for the years 1891 and 1S92; and Text Rook on Ordnance and Gunnery for Use at the Naval Academy, by Commander R. R. Ingersoll, U. S. N.
For further information in regard to armor, see BALLISTICS (under Ballistics of Penetra tion) ; SNIPS, ARMORED; also PROJECTILES and C UN S, NAVAL.