Ammunition with penetration or anti-armor capacity called AP (Armor Piercing) is a type of high-speed projectile thanks to its metallic layer that covers the projectile, making it more aerodynamic, making it conserve power even at long distances.
The penetrating capacity of this type of projectile lies in its great inertia, since when it hits at a high speed it causes the external metallic covering to be annihilated thanks to the high kinetic energy, piercing the armor and leaving the projectile intact to penetrate inside the hull by the opening generated by the cover.
Another variant was the ammunition (APHE) that, when penetrating the hull using the same principle as the PH, also exploded since it contained an explosive charge, this being the most destructive and dangerous variant.
The countermeasures that the tanks could adopt was to increase the thickness of the armor, but this was counterproductive and had a limit due to the increase in weight and that was why it ceased to be an option, so a type of hollow armor was developed, formed by a thin layer an empty space and a core that was effective for a time.
Another solution against APHE was reactive armor, which consists of metal plates sandwiched with a plastic explosive that are placed in the vulnerable parts of the armor.