It is not yet known whether the thickest armor will resist any shot that can be hurled against it; whether, in other tvords, the thickest practicable armor will overcome, or be overcome by, the heaviest practicable shot. Experiments at enormous cost have been conducted by the government for some years to determine this important question: a natural result has been that cannon are made larger and larger, and armor-plates thicker and thicker, in the struggle between artillery and ship-building. The experiments (so far as England is concernedy have been conducted principally at Shoeburyness, but also on board the Powderer at Portsmouth. The usual mode is, to construct a target resem bling the armed side of one of our iron•clads, and then to try to pierce it with shot fired from guns at various distances. A Warrior target, for instance, consists of a 4.1--im armor-plate, backed by 18 in. of teak, and an inner skin of fin. iron; while a Lord Warden target has 4t in. plate, 30 in. teak, and 1i in. skin. A few examples will serve to illustrate the method of proceeding.
In Aug., 1866, a Warrior target was built up at Shoeburyness—i.e., a target similar in strength and construction to the side of that ship. Alderson's steel shell, Armstrong's conical shell, and Palliser's chilled-iron shell were fired at it from a 7-in, gun at 00 yards: the Palliser shot excelled the others, going clean through the target, armor and all, and bursting behind. On another occasion, a Palliser 115-lb. shot went through the target even at an angle of 30° from the perpendicular. The Lord Warden target has been pierced by 9i and 10-in. shot at a distance of 1000 yards; while the thinner Warrior target was pierced at 2000 yards. The Bellerophon and Hercules targets were more ponderous.
At the end of 1878, the British navy consisted of 64 ships afloat or building, of which 46 were efficient. They were divided into five classes, the first two of which contain only the formidable turret-ships. The armor of the first, class, comprising 4 ships, ranged from 12 to 24 in. in thickness: the Inflexible. has armor from 16 to 24 in. The second class, of 9 ships, has armor from 8 to 14 in. thick. The third, of 16 ships, from 5 to 12 in. The fourth, of 4 ships, from 6 to 10 in. In the fifth class, 13 ships, the armor is from 4i to in. The last class comprises the old iron-dads, the Warrior, Black Prince, and others.
Armor-clad forts are also attracting lAtention. Iron has been used largely in the defenses of Plymouth and Portsmouth. In 1864, a line of iron-clad fort was built up at Shoeburyness, to test several modes of construction. In the same year, the Russian government employed the MbMwcil company to build a shield, as an experiment for the defenses of Cronstadt. The front was made of 12 in. thick of iron in horizontal bars; this was backed by 14 in. of thickness in upright bars; and the whole strengthened with enormous struts, brackets, ribs, and dovetails of iron. The shield • was to form the facing or armor for a battery of three of Krupp's 600-pounder steel guns, and measured 43 ft. by 10. The shield, with its foundation-plate, weighed 140 tons. In
one experiment at Shoebury, a plate 13 in. thick was placed in front of a mass of gran ite 14 ft. thick, and fired at with 200-pounders: four shots cracked the granite, although the plate was not pierced. The Americans made an experiment in Chesapeake Bay, in Sept., 1800, on a temporary fortification, made of enormous granite blocks faced with 10-in. armor; shots of 430 and 690 lbs. were fired from Rodman guns, at a range of 350 yards, and eleven such shots destroyed the whole fabric. The Thu nderer has been fitted up as a target-ship at Portsmouth, partly to test very thick plates at very short dis tances. The plates are fastened to an enormous bulkhead near one end of the ship, and the guns placed near the other end. On one special occasion, a Palliser 115-lb. chille shot, with nu: extra charge of powder fired at 25 ft. off, went clean through a 7-in. plate and 45 in, of teak bulkhead. On another occasion, soon afterwards, a Hercules target, with a 9-in. plate, was fired at with an 8-in. spherical shot at 30 ft.; the shot made a (lent 24- in. deep, but did not further disturb the plate. The 24-ia. armor of the byte xi-. Me is divided into two 12-in. plates, with 9 in. of teak between—the theory of this arrangement being that the outer plate, even if pierced, will shatter the shot, which will then be stopped by the inner armor. Dr. Collis Brown has suggested a system of sloping armored sides which would give a ship armor of 36 in. at any given point in a displacement not exceeding that of existing iron-clads. In the trial of the 190-ton Arm strong gun at Spezzia, a steel armor-plate was fired at, and the shot, though it pene trated the plate, was stopped in the backing.
Regarded as articles of manufacture, armor-plates were at first produced mainly by hammering, several thicknesses of iron being welded one upon another, at a white heat, by blows of a ponderous steam-hammer; but it is now more customary to produce them by rolling than by blinnnering—pressure being considered to produce more satisfactory results than percussion. Whatever the thickness of the slab is to be, operations are commenced with plates about an inch thick: these are heated, rolled, cut, piled up, heated and rolled over and over again, until the required thickness is produced. The rollers are placed further and further apart, as the slab becomes thicker and thicker. Souse of them are truly enormous masses of metal, solid cylinders 8 ft. long by 32 in. diameter. At the Atlas works of Messrs. Brown & Co., Sheffield (the chief manufac tory for armor-plates), there has been produced a rolled slab 17 ft. long, 7 ft. wide, and 14 in. thick, weighing 30 tons. At Gritser, in Germany, some excellent armor-plates of chilled (cast) iron have been manufactured. For armor-plates, the metal is very scrupu lously selected, and every part of the processes conducted with great caution.