12 in. round the turrets. These turrets were 14 in. maximum thickness. During the above period (1859 to 1873) we have noticed that, owing to successive improvements in guns, continuous increase 2 -BREAST WORK 10. COAL COAL. W.L. " 10. had to be given to the thickness of armour protecting the ships, and a stage was at length reached when it was found impossible to cover any large area of a ship's side with armour thick enough to resist the fire that could be brought to bear against it. The next development accordingly consisted in only attempting to protect a portion of the ship with very thick armour, and to depend on deck and other protection for the remainder. The principle acted upon was that it would be better to efficiently protect the midship portion of the ship in way of machinery and heavy guns, than to cover a large area with thinner armour that could not keep out the enemy's fire. This principle was carried to its extremest limit in the Inflexible. FIG. 125A.-H.M.S. Devastation. "Inflexible" (1874). This ship was 320 ft. long and 11,880 tons. The armoured citadel (Fig. 126) was 110 ft. long, with a maximum thickness of 24 in., the armour being in two thicknesses. Forward and aft of this citadel the magazines, etc., were protected by underwater decks, 3 in. thick, and some protection was afforded by the stowage of coal and cables on these decks, with cork packing at the sides and cofferdams, as shown. In this ship the hull armour was still of iron, but the outer thickness of the turret armour, 9 in., was "compound," or steel faced. Figure of Merit of Armour. The resistance of armour to penetration is compared with the penetration of wrought iron as found by some empirical formula. There are a number of these formulæ, the one used in England being that obtained by Captain Tresidder (see "Gunnery Manual"). He found that penetration of wrought iron could be represented by the formula The ratio of the thickness of wrought iron as found by this formula to that of the armour plate tried is termed the figure of merit. The plate EXAMPLE.-A 6-in. armour plate is attacked by a 6-in. 100-lb. Holtzer armour-piercing shot with 2177 ft. per second striking velocity. resists penetration, find the figure of merit we have t2 = 100 × (2177)3 X 1 693,500,000 for wrought iron. By using logarithms t is found to be 157 in., so that the figure of merit is 2.6. Compound Armour.-A compound armour plate consists of a wrought-iron plate artificially attached to a steel face of about half its own thickness, the result being a plate with hardness of steel on the face by which projectiles are broken up, and toughness of wrought iron at the back which prevents cracking taking place. As at first made this armour had a figure of merit of about 14, but improvements in manufacture brought up the ratio to 17. In France all steel plates were used, but experiments showed that this material was lacking in toughness, and trouble was caused by the spontaneous cracking of these plates. Compound plates were Inflexible up to and including the FIG. 127A.-Section Admiral class. used in ships after the Royal Sovereign (1889). Admiral Class.-The next distinctive type of ship was that known as the Admiral class (1880). The various ships of the class differ somewhat in detail, but their main features are the same. The Collingwood, 325 ft. long and 9500 tons (Figs. 127 and 127A), may be taken as a typical ship of the class. The armour belt was 18 in. thick amidships, 7 ft. 6 in. broad, and it extended for a length of 140 ft., or about seven-sixteenths the length of the ship with athwartship bulkheads. No protection save coal was provided above this armour belt. Forward and aft were two sloping barbettes of 11 in., with trunks coming down within the limits of the armour belt as shown. The floor of these barbettes was 3 in. The ends of the ship were unprotected by vertical armour, but underwater decks were worked 2 in. in thickness. The top of the belt was covered in with a level deck 2 in. thick. While this class of ship was building, quick-firing guns and high explosive shell were being developed, and although only 6-pounder shell were projected, yet it was felt that the large areas of unprotected side in these ships was an element of serious danger. The influence of this factor is seen in the Nile and Trafalgar (1886), and in the next main type of ship, the Royal Sovereign class. "Royal Sovereign" (1889).-This ship was 380 ft. long and 14,150 tons displacement. There were eight of the class built, seven with barbette mountings for the heavy guns (Royal Sovereign, Ramillies, Repulse, Royal Oak, Resolution, Revenge, Empress of India), and one with turrets (Hood). The former ships were able to obtain a greater height of big guns above water than the Hood on account of the weight involved in the turrets. In these ships the waterline belt was 8 ft. broad, with a maximum thickness of 18 in., covered in with a horizontal deck 3 in. thick (see Figs. 11 and 128). The length of the belt was 250 ft., or two-thirds the length of ship. Bulkheads, 16 in. and 14 in., closed in the belt at the forward and after ends respectively. The one-sixth of the length at the ends had underwater decks 2 in. thick. Above the 18-in. belt, from middle to main decks, 4-in. armour is worked, with an upper coal-bunker behind. This armour was of nickel steel, and was fitted in order to determine the explosion of shell filled with large bursting charges of high explosive outside the ship, and to prevent the free perforation of the side above the belt by the smaller nature of quick-firing guns. The barbettes mounting the 13-in. guns were pear-shaped and of very substantial construction, the maximum thickness being 17 in., and the armour extending right down to the middle deck. The armour for this class was compound, except the 4-in. side, which was of nickel steel, and the main deck casemates of steel. Harveyed Armour.-The next large group of ships were those of Majestic class, nine in number. In these ships armour made by the Harvey process was adopted. This armour is estimated to have a figure of merit of about 2, as against 17 for compound armour. The development of armour-piercing projectiles of forged steel was the cause of this improvement in armour manufacture. In the Harvey process an all steel plate is used, and the face is cemented, i.e. animal charcoal is placed next the face of the plate (two plates being usually dealt with together, face to face), and the whole is covered in with bricks and run into a gas furnace, where it remains two to three weeks, seven days or so being allowed for cooling. In this way the proportion of carbon on the face is increased, and the front is then capable of being hardened. The plate is first cemented as above, and then bent to the required shape and all necessary holes made in the surface. It is then heated and the face douched with cold water, which makes the front of the plate exceedingly hard. We thus have a compound plate, but the junction between the hard face and the tough back is much more perfect than in the compound plates. The object to be attained was a steel plate, without welds, having such a proportion of carbon in the surface that water cooling would produce a very hard face. As the thickness of the hard steel is practically constant for all thicknesses of plate, it follows that thin plates obtain relatively higher values of the figure of merit than thicker plates. That is, a 12-in. plate is not twice as good as a 6-in. plate. For Harveyed armour a figure of merit of 2 may be taken, for thinner plates (6 in.) 24. Majestic" (1894).-There are nine ships in this class (Majestic, Magnificent, Mars, Jupiter, Hannibal, Illustrious, Victorious, Prince George, Caesar). They are vessels of high freeboard, and are 390 ft. long and 14,900 tons (Figs. 129 and 130). A new departure |