Maitland's latest formula, now used in England, is
General Froloff, Russian army, gives
for plates less than two and one-half inches thick, and
for plates more than two and one-half inches thick.
If θ be the angle between the path of the projectile and the face of the plate, then v in the above formulæ becomes v sin θ.
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.