High Quality Content by WIKIPEDIA articles! An armor-piercing (AP) shell is a type of ammunition designed to penetrate armor. From the 1860s to 1950s, a major application of armor-piercing projectiles was to defeat the thick armor carried on many warships. From the 1920s onwards, armor-piercing weapons were required for anti-tank missions. Furthermore it is used to defeat concrete, ballistic vests, bulletproof glass, and other defenses.