A recent British study provides a statement of the general principles
governing the attack of, and defense by, spaced armor. The essential points
bearing on the use of spaced armor by the enemy, that follow, are taken from
the British report.
* * *
Two separated homogeneous plates attacked by A.P. shot, or 2 separate
plates in loose contact, are less effective in defense than a single plate of the same
total thickness. This is because there is no shearing resistance over the internal
A front cemented (face-hardened) plate separated from a rear homogeneous
plate attacked by A.P.C. (armor-piercing capped) shot will, for the same reason,
offer less resistance than a single cemented plate of the same total thickness.
A front homogeneous plate separated from a rear cemented plate offers
increased resistance to A.P.C. shot as the front homogeneous plate destroys the cap
of A.P.C. shot and so diminishes the effectiveness of the projectile against the
cemented surface of the rear plate. The important point in this construction is that
by the use of spaced plates the cemented face can be made to be an interior surface
of the system, and so afford protection against an A.P.C. shot de-capped by the
For the same reason a rear cemented plate offers increased protection
against a tungsten carbide cored shot, unless the core is very well protected by a
cap and some form of cushion.
A rear cemented plate will also offer greatly increased protection against
an A.P. shot because the nose of the A.P. shot will be partly damaged by the front
homogeneous plate, and so will have a still further diminished power against the
cemented surface of the internal plate.
From the point of view of attack, the effectiveness of capped (A.P.C.) and
uncapped (A.P.) projectiles varies in different calibers owing to a differing balance
of advantages and disadvantages. Though a cap tends to preserve the point of the
ogive (the curved and pointed head of the projectile) during perforation of the front
plate, the cap itself is destroyed by the same action, and thus kinetic energy is
wasted. In one caliber the reduction of energy due to loss of the cap before reaching
the interior plate may result in failure to perforate, whereas in a larger caliber the
loss may have a less pronounced effect on the ultimate performance, resulting in
perforation of 2 plates of the same quality and equally well matched.
It is true that an A.P. or A.P.C. shot tends to turn towards the normal
on perforating a plate, but in the case of spaced armor any advantage which might
be gained thereby is likely to be neutralized by the acquisition of a transverse
angular velocity which may result in increased yaw. For this effect to be
appreciable, plates should be separated by a distance of at least one caliber.