P = ------ - 1.5
d² 400

[TEX: P = \frac{w \ v}{d^2 \ 400} - 1.5]

for plates more than two and one-half inches thick.


If [theta] be the angle between the path of the projectile and the
face of the plate, then v in the above formulæ becomes v sin [theta].

When we come to back the plates, their power to resist penetration
becomes greater, and our formula changes. The Gavre formula, given
above, is used to determine the velocity necessary for a projectile to
pass entirely through an iron plate and its wood backing.

Compound and steel armor are said to give about 29 per cent. more
resisting power than wrought iron, but in one experiment at the
proving ground, at Annapolis, a compound plate gave over 50 per cent.
more resisting power than wrought iron.

The Italian government, after most expensive and elaborate comparative
tests, has decided in favor of the Creusot or Schneider all-steel
plates, and has established a plant for their manufacture at Terni,
near Rome.

The French use both steel and compound plates; the Russians, compound;
the Germans, compound; the Swedes and Danes use both. Spain has
adopted and accepted the Creusot plate for its new formidable armored
vessel, the Pelayo; and China too has recently become a purchaser of