Page:1902 Encyclopædia Britannica - Volume 25 - A-AUS.pdf/725

 ARM OUR 671 cases ; for example, the armoured belt of a cruiser and that iron back or foundation. This armour possessed the of a battleship. The former is the thinner, and more liable advantage of a harder face, than “ all steel ” plates of that to be overmatched by a shot, but a cruiser is not likely to date, combined with a tenacious back, and was adopted be long exposed to attack. The thick belt of a battleship and largely made on the Continent; but long courses of is less likely to be overmatched, but the vessel is more competitive trials eventually proved that the “ all steel ” likely to be kept in continuous close action ■ consequently plates made by Schneider, and subsequently by other the belt of the cruiser might preferably be made harder makers, were superior to the compound, mainly because than that of the battleship • and though such a distinction the soft wrought-iron foundation gave insufficient support, has never been recognized, and may be regarded as a though in one trial at Shoeburyness when fixed on granite refinement, it may have had influence, especially in re- a remarkable result was obtained. tarding the adoption of nickel in medium armour, noticed In 1890 important competitive experiments in Eussia hereafter. The power of guns to destroy hard and soft and America brought out the value of two features of an armour is greatly affected by the fact that the former entirely different character: first, a hard surface, and requires to be shattered, the latter perforated. So far as secondly, the ingredient nickel in steel. These are so the shot holds together on impact, shattering depends on important that they deserve to be dealt with separately. its striking energy, while perforation depends directly on The steel face of the compound plate was, as above the energy, but nearly inversely on the calibre of the shot noticed, harder than that of early “all steel,” but this and consequent size of hole to be made. Thus for many hardness was due to the employment of a front plate of years a new type 6-inch and an old type 10-inch gun were harder steel throughout its mass than was deemed suitable on board the Settle at Portsmouth. The energy of the for the foundation. Efforts were now made to impart latter was about double that of the former, and its shatter- excessive hardness to the actual surface or skin of a plate ing power was probably proportionately greater, i.e., about by the application of water-jets on a system proposed by double; but its velocity was less, and the perforating Captain Tresidder, who found that water thus projected power of the two projectiles was nearly the same. Thus against hot metal came in actual contact with it, and against Gruson’s shields the old heavy gun would deliver produced a degree of hardness which was prevented in far the heavier blow, Avhile the new type light gun would ordinary plunging by the formation of steam. About the perforate any ship’s side that was open to the attack of same time Harvey in America perfected a process of the 10-inch gun. carbonization applied to the front of armour plates. This As noticed above, British coast armour is made of could be extended to some inches in depth, and with it wrought iron, and is consequently liable to some evils was associated an application of water to the face, but of a from which Gruson’s chilled iron is free • that is to say, it less perfect kind than on the Tresidder plan. It was found is conceivable that it might be perforated, though it is that a shot which would perforate a plate with an ordinary made thick enough to make this unlikely. Bolts might untreated face might be completely broken and defeated fly under a heavy blow, and injury might be done by these by a very hard skin. Successful resistance apparently deand other pieces of metal, or debris forming what is termed pends on the fracture of the shot point or extreme tip on “ longridge.” On the other hand, the plate upon [date or first contact. On the fracture of the tip, penetration sandwich system lends itself to future alterations and becomes much more difficult, Avhile the shot is still laterally additions that are impossible with Gruson’s armour, which unsupported, so that the latter may break outAArards on has finality stamped on it, and might become a trouble- the same principle as an arch may yield laterally under some hindrance. Every preparation is, in fact, made for pressure applied to the centre. Palliser chilled shot indeed the addition of extra front plates to the armour on British often broke on ordinary plates so completely that white coast forts, which can be removed, altered, or strengthened radiating splashes were made by the minute particles flying with the least conceivable labour. The best armour now across the plate face. At the date when Harvey and made is intermediate between hard and soft, but generally Tresidder plates came in steel projectiles had superseded yields by perforation more than fracture. Steel armour those of chilled iron. These steel projectiles had tough plates, although tried from time to time, long proved bodies, AArith heads hardened by water or oil, and combined brittle, and gave little promise of success. In October the penetration possessed by a hard point Avith considerable 1876, however, was commenced at Spezia a series of trials power to remain intact, so that steel shot would strike an which undoubtedly led to the immediate adoption of steel ordinary steel plate at a fairly high velocity, penetrate to in one or another form by the principal Powers. In these a considerable depth (perhaps more than a calibre), then trials targets representing the proposed belts of the Italian bound back a long way towards the firing point, and yet battleships Duilio and Dandolo (then under construction) suffer such inappreciable deformation or internal injury as were erected. All were made of the same thickness, i.e., to be capable of being repeatedly fired at armour, and of nearly 22 inches of metal, but differed in the fact that iron repeatedly behaving in the manner described. and steel were used by different makers. These shields On faces hardened by the Harvey and Tresidder prowere attacked first by 10-inch, and subsequently by 17 '7 2 cesses, Avhich soon became combined, excellent steel inch (100-ton) guns. The lighter projectiles lodged harm- projectiles not only broke, but became so completely lessly in the soft iron, but produced serious cracks and disintegrated at times that the white splash mentioned as fractures in the steel. On the other hand, the enormous characteristic of the defeat of chilled iron shot was seen; 2000-lb projectiles of the 100-ton gun passed through the and a very curious device has been adopted to enable the wrought-iron plates very easily, while the steel plates shot to hold together, namely, a wrought-iron or steel cap stopped them, though at the cost of their own complete applied to the shot point. It had been discovered accidestruction. The resisting power of steel was seen to be dentally at Shoeburyness in 1877 that a chilled shot which so disproportionate to that of iron that its adoption in was defeated by a certain compound shield would perforate some form was a mere question of time. In England the it when an additional plate of wrought-iron 2| inches liability to fracture was thought so objectionable that great thick was added in front of the shield, the explanation efforts were made to secure toughness in some form; and being that the additional resistance afforded by this soft the Sheffield makers, Cammell and Brown, brought forward plate by no means compensated for the fact that the shot what are termed compound or hard-faced plates, each kind point entered easily, and was well supported and saved consisting of a hard steel face cemented to a soft wrought- from fracture before it encountered the steel. Colonel