Artillery, weapons, including cannon and missile launchers, that fire projectiles larger than approximately one-half inch (13 mm) in diameter. In the United States, any gun or launcher which makes use of ammunition 1 inch (2.5 centimeters) or more in diameter and that is not fired from the hand or shoulder is called artillery. These weapons normally fire high-explosive projectiles that can reach targets far beyond the range of small arms such as pistols, rifles, and machine guns. An artillery battery consists of two or more pieces (the general term used for individual weapons) of the same size and type that are usually controlled and fired together.

Artillery is also the name of the branch of an army that mans such weapons. Artillery is one of the three main combat arms, the others being infantry and armor (tanks). The distinction between these three arms is not primarily one of weapons—since tanks are armed with artillery-size guns and even infantrymen fire such artillery pieces as mortars and recoilless rifles—but of how the weapons are used.

In the artillery, the weapons are placed some distance behind the fighting front and the projectiles pass over the heads of friendly troops. The guns are used to inflict casualties and destroy or damage enemy defensive positions before an infantry or tank attack; to break up an enemy attack before the attackers come within range of infantry weapons; to harass and demoralize enemy troops; and to destroy enemy artillery, tanks, trucks, aircraft, or ships.

Artillery fire is generally more accurate than aerial bombing, and can be kept up day and night in any weather. Accuracy comes from the use of various fire-control instruments—including telescopes, range finders, lasers, and radar—and mathematical calculations based on data obtained with these instruments and the known characteristics of the guns and ammunition being fired. Forward observers, either on the ground or in the air, play an important role in directing artillery fire.

Armor plate, such as that used on tanks and naval vessels, provides some defense against artillery fire. Concrete bunkers and blockhouses are effective, but they limit the mobility of the defending troops. The main defense of the infantryman is usually a foxhole or underground bunker. Helmets and body armor provide some protection against stray shell fragments and flying debris. Active defensive measures include artillery or air attacks on the enemy guns.