One common addition to later shells is the use of a softer ring or cap of metal on the nose known as a penetrating cap.

Shells designed for this purpose have a greatly strengthened body with a specially hardened and shaped nose. An armor-piercing shell must withstand the shock of punching through armor plating.

These lightweight shells were fired at very high muzzle velocity and retained that speed and the associated penetrating power over longer distances. In the anti-tank role, as tank armor improved during World War II newer designs began to use a smaller but dense penetrating body within a larger shell. The AP shell is now seldom used in naval warfare, as modern warships have little or no armor protection. AP rounds smaller than 20 mm are typically known as 'armor-piercing ammunition', and are intended for lightly-armored targets such as body armor, bulletproof glass and light armored vehicles. From the 1920s onwards, armor-piercing weapons were required for anti-tank missions. From the 1860s to 1950s, a major application of armor-piercing projectiles was to defeat the thick armor carried on many warships and cause damage to the lightly-armored interior. An armor-piercing shell, armour-piercing shell in Commonwealth English, AP for short, is a type of ammunition designed to penetrate armor.

Force behind a tank shell