458 
PRINCIPLES OE GUNNERY. 
of In order to investigate more fully the question of the penetration of 
armour-plates, it is necessary to consider the form of head and the 
material of the projectiles employed. 
Several forms of head have been experimented with in this country 
—viz., flat, ogival, hemispherical, and conoidal. The ogival head 
struck with a radius of 1| diameters has been adopted for Palliser 
projectiles, as experiment has shown that this is the most suitable 
form for the penetration of armour-plates. An ogival head of two 
diameters has also given good results. The ogival head acts more 
as a wedge, and it consequently gives better results in penetration 
than the flat head, especially with thick solid plates. The flat head 
acts like a punch, driving the material of the armour-plate in front of 
it. This no doubt increases the resistance which a flat-headed pro¬ 
jectile meets with in penetration. 
The flat head is superior to the ogival, (1) when firing through 
water, (2) when firing at extreme angles of oblique fire. In the first 
case, a ship^s side is more likely to be hit below the water-line by a 
flat-headed than by an ogival-headed projectile, since the ogival-headed 
projectile has a greater tendency to be deflected upwards by the water; 
in the second case, the ogival-headed projectile glances off the target 
where a flat-headed projectile would penetrate. A steel flat-headed 
projectile will penetrate at an angle of impact with the surface of the 
plate of about 80°, while the ogival-headed projectile of the best form 
will hardly penetrate at a less angle than about 40°. 
If v is the velocity required for a projectile to pierce an armour-plate 
with right-angled impact AO, its energy per inch of circumference 
2ff . ird 
But if the projectile strikes obliquely, as BO, at an angle of impact 6, 
then, if it turns in on its point and perforates normally, it is readily 
seen that the velocity for perforation must be and consequently 
the energy per inch of circumference for oblique perforation will be 
JFffi 
2 gird . sin a 0 3 
so that in this case the number of foot tons per inch of circumference 
to perforate an armour-plate obliquely is found by dividing the 
