ARTILLERY IN COAST DEFENCE. 
413 
Besides battleships and gunboats there are in all navies armoured 
and protected cruisers; the former having vertical, the latter only 
horizontal armour. None of them are likely to engage coast defences; 
in the armoured class the armour is too light to ensure protection 
against the lightest armour-piercing guns, and with very few exceptions 
the armament is entirely unprotected. 
Before we can determine on the rules which should guide us in the 
choice of a method of attacking a ship of given type, we have to con¬ 
sider the powers and uses of our projectiles. 
First, as regards the attack of armour. Armour, as applied to ships, 
is of three kinds, viz., wrought-iron, steel, and steel-faced iron, usually 
called compound; these three varieties behave differently under attack. 
Wrought-iron yields locally; it is punched or perforated, a clean hole 
being made in it. The entire shield is generally capable of resisting 
a subsequent blow as stoutly as it resisted the first. Partial penetra¬ 
tion is practically useless, however often it may be repeated. 1 2 It is 
obviously therefore useless to attack this species of armour unless the 
power of the gun is equal to driving its projectile through the armour. 
A measure of the power to penetrate is given by the rough rule that, 
in order to penetrate its own diameter into wrought-iron, a shot must 
strike with a velocity of 1000 f.s., and its penetration with greater or 
less striking velocity will be in proportion; thus, a 10-inch shot strik¬ 
ing with 1000 f.s. will penetrate ten inches of wrought-iron armour, with 
500 f.s. it will penetrate five inches, and so on. 
This rule gives the penetration which may be expected when the shot 
strikes the plate in a line normal to its surface; when it strikes at an 
angle, the thickness of plate that can be perforated is in proportion to 
the sine of the angle at which it strikes; thus, it may be useful to 
remember that striking at 60 degrees to the surface a shot will 
penetrate roughly six-sevenths of the thickness it would penetrate at 
the normal. Below 50 degrees the shot will glance from wrought-iron; 
from hard armour the shot will glance below 65 degrees. 
Steel-faced and steel, called “ hard ” armour, yields by fracture, the 
plate cracking radially from the point of impact, these cracks extend¬ 
ing through the thickness of the metal in the case of steel (soft steel, 
however, occasionally has been perforated, behaving more like wrought- 
iron). These armours not admitting of perforation, as a rule, 3 can only 
be destroyed by repeated blows, cracking, and stripping off the plate. 
Though a heavy gun with a single shot may not effect much against 
them, repeated blows from lighter guns may succeed in destroying the 
armour and eventually penetrating the ship's side. This, at consider¬ 
able range, or against a ship in motion, would obviously be a difficult 
task to accomplish. In the table of penetrations given in the Tactical 
Manual, a note states that damage equivalent to penetration would be 
effected against hard armour of the same thickness as wrought-iron, 
which would be just penetrated by the gun; it is important to under- 
1 Attack of Armour. Captain Orde Browne. Vol. XV., p. 308. 
2 Major MacMahon, R.A., gives the following rule for ascertaining the penetration of compound 
armour by steel shot. The penetration is equal to four-fifths of the calibre of the shot for every 
1000 f.s. striking velocity. Thus, the steel shot of the 10-inch B.L. gun will penetrate 8-inch 
compound armour with 1000 f.s. striking velocity. 
