Heavily armored vehicles used by a military force. Also refers to a branch of the US Army that fights primarily with such vehicles, chiefly tanks and, to a lesser extent, armored personnel carriers.

Armor warfare has been important to armed forces around the world since World War I, when it was effective against entrenched ground troops. World War II was the scene for massive tank battles, especially on open steppes of the Eastern Front and in the deserts of North Africa. Armor was also used in support of infantry operations, even in dense jungles and city fighting in the Vietnam War.

Armor units can advance quickly and break through enemy lines to wreak havoc on supply and command and control units in the rear. Soviet strategy in Cold War Europe depended heavily on breaking through thin Western lines, attacking with huge masses of armor.

Armor units are fought with air power and other armor units. Infantry is also usually equipped with anti-armor weapons, such as small, shoulder-mounted missiles. Mines, though no longer used (officially...) in warfare can also destroy or immobilize armored units. Modern tank-hunting helicopters (the US Army's AH-64 Apache, for instance) and aircraft (A-10 Warthog) are specially designed to kill tanks.

Facing a tank must be scary as hell if you're an infantryman. Watch the last battle scene from Saving Private Ryan to get an idea.