A model for rigid projectile penetration and perforation of hard steel and metallic target plates is suggested. The intended application is in computer programs for assessment of effects and vulnerability. The target material resistance to penetration is assumed to be the sum of nose resistance and friction along the part behind the nose. The nose resistance increases initially with the penetration depth to a constant value, which corresponds to lateral displacement of the material along the projectile trajectory. The friction also increases from the start and becomes constant when the rear end of the projectile passes the front face of the target. When the front end of the projectile is sufficiently close to the rear surface, then the remaining volume of target material in front of the projectile is crushed and forms fragments. At the penetration depth where this occurs the force required for crushing equals the force required for continued lateral displacement of the target material. The fragments are ejected with the same velocity as the projectile.