PRINCIPLES OE GUNNERY. 
455 
The different materials used in the construction of armour-plates— Materials 
e.g., cast-iron, wrought-iron, and steel—will next be considered with armour! 
respect to their comparative advantages or disadvantages for resisting plates, 
the fire of heavy guns. 
There are two methods of destroying armour-plates, which may be 
employed according to circumstances—viz., punching and racking . 
For punching, a high velocity is given to the projectile, of a com¬ 
paratively small diameter, in order to drive it completely through 
the armour-plate, when the fragments of the projectile take effect on 
the guns, &c., behind it, and make a hole which if near the water-line 
of an iron-clad ship soon places it hors de combat. If, however, the 
armour-plate is so thick that it cannot be perforated, racking may be 
resorted to— i.e., expending the energy of the projectile on cracking 
the armour and shaking it from its supports. This may be done most 
effectually with projectiles of comparatively large diameter and low 
velocities; the object being in this case not to penetrate but to break 
up the armour. It will be seen (p. 457) that wrought-iron plates 
yield to punching and resist racking, while steel plates of similar 
thickness yield to racking and resist punching. 
The effect of projectiles on a cast-iron target is very destructive: cast-iron, 
the cast-iron cracks and flies, and in its ordinary condition it is not 
suitable for employment for defensive purposes. Chilled iron armour 
may be used in some places, where it is not likely to be subjected to 
continued bombardment, but the thickness required to resist fracture 
is much greater than that required by wrought-iron under similar 
circumstances. 
The effect produced by a projectile on a wrought-iron target is less wrought- 
destructive than upon cast-iron. Owing to the superior toughness iron * 
and malleability of wrought-iron, there is not such a tendency to crack, 
and break up into fragments. A large number of experiments have, 
from time to time, been carried out at Shoeburyness in order to test 
the requisite thickness of wrought-iron plates to resist perforation.* 
Iron plates are made either with the requisite thickness of iron in a 
single solid plate, or the thickness is made up of two or three iron 
plates interlined with wood. The former are called solid plates, the 
latter laminated plates. 
There are differences of opinion as to the relative merits of the two 
systems, when applied to the protection of ships or batteries. On the 
one hand, it appears that the laminated plate is more easily perforated 
than a solid plate of the same thickness. Colonel Inglis, li.E., con¬ 
siders that the resistance of arm our-shields 7 ins. thick, composed of 
one, two, or three equal layers, are respectively as 100, 96, and 89 ; 
and that a single plate 17-| ins. thick is about equal to three 6|-in. 
plates separated by 5-in. layers of teak. On the other hand, the 
laminated plate system admits the employment of a wider plate; the 
plates themselves being more easily and soundly manufactured. In 
Vide “ Extracts from the Proceedings of the Department of the Director of Artillery.” 
