Page:1902 Encyclopædia Britannica - Volume 25 - A-AUS.pdf/724

 670

ARMOUR

which, although it has never attracted much attention in England, is used almost universally in European coast forts. It was proposed and made by Gruson of Magdeburg, and consists of massive shields of chilled cast iron, which are easily made of any required form. No backing or bolts are used, the shield being built up of heavy blocks, if possible cast on the spot, which are keyed together, and constitute the entire parapet (see Fig. 3). The metal can be made

by it. Soft armour plates, such as those of good wrought iron, do not break under the impact of shot, but yield by perforation. Thus a projectile Avith sufficient striking energy passes through soft armour, making a more or less clean hole, but leaving the plate practically as strong as before. A shot, however, that fails to perforate, effects nothing, lodging harmlessly in the shield. Hard armour, on the other hand, of which chilled iron furnishes the most extreme example, refuses to yield by perforation, and i disintegrated, the whole mass before long parting in fragments. Hard armour offers a complete defence against a covered by it being entirely protected until their shield is destroyed. On this account chilled iron shields have been used to protect coast artillery from the few rounds that the heavy guns of men-of-war may be expected to deliver during an attack of limited duration. Notable examples of Gruson’s shields and forts are the St Marie battery near Antwerp (see Fig. 3), cupolas at the entrance of the Weser near Bremerhaven, and two turrets defending Spezia harbour, each mounting two 119-ton Krupp guns (see Fig. 5). The joints shown in this figure indicate that the
 * breaks up the shot on impact; but it gradually becomes
 * few rounds from very heavy guns, men and ordnance

Fig. 3. of thickness varying according to the supposed needs of each part of face or roof, and the breech-loading ordnance, at that time existing on the Continent, but not in England, allowed the use of shields sloping down forward at the gun forts in curves well adapted to cause shot to glance off them. In British coast forts vertical walls were adopted, covered with Avrought-iron plates, either applied in a single thickness, or in successive layers sandwiched with wood or concrete (see Fig. 4). Thus British coast

1

Fig. 4. armour differed fundamentally from that employed by other nations, and this difference is maintained to the present time. These two kinds of coast shields deserve attention as furnishing examples of the opposite extremes in character, and as justifying the classification of armour plates into “soft” and “hard” kinds, a distinction which must be kept in view in order to understand the power of artillery fire, and the behaviour of armour when attacked

1 1 t Fig. 5. turret roof is built up of fifteen sector-shaped pieces and tAvo centre plates of semicircular form. Before adoption a sector piece was subjected to three blows from projectiles fired from an Elswick 100-ton breech-loading gun. A fourth round indeed was afterwards delivered, as well as some rounds from 15-cm. (5‘9 in.) guns. This shield was fractured in several directions, but the fragments remained in situ, and the defensive power of the shield was probably but little diminished, and would continue until some large fragments should become displaced. Soft armour, until recently best exemplified by Avrought iron, but now by soft nickel steel, exhibits its capacity most fully in inland fortifications, where it may be called upon to resist the breaching attack of siege guns of such limited weight and power as not to be able to perforate it completely. First-class soft armour might bear such an attack for hours and days, or perhaps even for weeks. The continued breaching attack of inland forts by siege guns of limited weight, and the brief attack of coast shields by the very heavy guns of battleships, illustrate the conditions which bring out most completely the powers of soft and hard armour. Between these lie innumerable