Artillery Types

Artillery is generally divided according to size into light artillery, medium artillery, and heavy artillery. It can also be categorized by the trajectory, it imparts to the projectile. The size of an artillery weapon is usually expressed in terms of its caliber (the diameter of its bore) measured in millimeters or inches and fractions of inches. (In large guns, especially naval guns, the term caliber is also used as a measure of length. For example, a 6-inch 25-caliber gun is one with a bore diameter of 6 inches [152 mm] and an inside length 25 times the bore diameter.) The size of guns is occasionally expressed by the weight of the ammunition fired; thus a "six pounder" fires a projectile weighing six pounds (2.7 kg).

Army Artillery

Traditionally, artillery weapons were called cannon and three kinds were recognized—guns, howitzers, and mortars. They are defined by the kind of trajectory (path) followed by their projectiles. Guns and howitzers not mounted on tanks, ships, or aircraft are often called field pieces, or field artillery.

Field artillery is utilized to support infantry and armored forces. Generally, these weapons are dragged behind tractors or trucks or boarded on vehicles for their speedy execution. The size of the weapons ranges from guns firing 1-pound (0.5-kilogram) projectiles to those firing 350-pound (159-kilogram) projectiles. The caissons which were once used to carry ammunition for field artillery are now being replaced by ammunition trailers and tractors. The size of weapons is measured in millimeters, ranging from 75 to 125 millimeters. These weapons are put on tanks and tank destroyers. Field artillery is supplemented by surface-to-surface guided missiles.

Antiaircraft artillery refers to the bursting shells fired rapidly from antiaircraft artillery at a high angle. Generally, these guns are aimed at a target by electronic automatic fire control systems. The shells are exploded with the help of special fuses especially in the area of target. Antiaircraft guns are supplemented by surface-to-surface guided missiles.

Artillery also sometimes refers to the cannons on airplanes, helicopters and naval vessels.

A Gun

is a weapon that has a low, or nearly flat, trajectory—it fires projectiles in a nearly straight or gently curving line. A gun's barrel is long in relation to its diameter. Guns are used against airplanes and tanks and as long-range bombardment weapons. The main weapon of a tank is usually a gun. Guns used by the U.S. Army include the 20-mm automatic cannon (a type of rapid-fire gun); the 75-mm and 90-mm antiaircraft guns; and the 90-mm, 105-mm, and 120-mm tank guns. The United States armed forces no longer use guns as field pieces.

A Howitzer,

usually used as a field piece, has a higher trajectory than a gun—its projectiles follow a more pronounced curve. Guns have greater range than howitzers firing similar ammunition, but are less adaptable to firing over the heads of friendly troops or to reaching targets protected by hills.

The U.S. Army uses a variety of howitzers: the 105-mm towed field piece; the 155-mm field pieces, towed and self-propelled; and the 203-mm self-propelled field piece.

A Mortar

has a very high trajectory; its shells are fired high into the air and plunge almost straight down. Most mortars, unlike guns and howitzers, are loaded from the muzzle (front end of the barrel) rather than from the breech. Since they have short, smoothbore barrels (that is, barrels without rifling), they are short-range weapons of limited accuracy.

Until World War I, mortars were large weapons manned by artillerymen. In that war the trench mortar was developed, and it became an infantry weapon. This mortar, the type now used, consists of a tube resting on a heavy metal base. The shell is dropped down the muzzle. When it hits the bottom of the tube, an explosive charge that fires the shell is set off. The United States armed forces use 60-mm and 81-mm light mortars and a 120-mm heavy mortar.

These three traditional types of artillery weapons are still in use, but other kinds are now used as well. These include missiles, rockets, and recoilless rifles.

Missiles and Rockets

are of many types—from the infantryman's bazooka to nuclear-armed intercontinental ballistic missiles designed to destroy entire cities. Between these extremes are a variety of surface-to-surface missiles, such as the U.S. Army's Lance, which are used as conventional artillery. Missiles, like artillery guns, are also used as antitank weapons. Some are guided by wire and some by computer-controlled infrared devices. There are also many surface-to-air missiles used as antiaircraft weapons.

Recoilless Rifles

are lightweight guns of 50 to 120 mm that can be fired by infantrymen, who carry the rifles either by hand or by vehicles. These rifles fire shells that are the size of small caliber artillery shells. They have little or no recoil, and therefore do not need heavy carriages. The breech of a recoilless rifle is not closed tightly, as is that of a conventional weapon, but is designed to permit some of the powder gases to escape to the rear and thus offset the normal recoil.

Naval Artillery

Although the term artillery is generally limited to land-based weapons, naval guns are of similar design and are used in similar ways. Modern naval cannon are almost always guns, rather than howitzers or mortars. Gunnery at sea is more complicated than on land because the ship doing the firing is always in motion.

Naval guns and missiles are designed for bombardment of ships and shore targets, and for use against aircraft. Naval guns and missiles are used against shore targets for a variety of purposes—to destroy strategic installations such as piers or airfields; to neutralize fortifications prior to an invasion or raid; and to support friendly troops already ashore.

The largest guns normally in service are the 8-inch (203-mm) and 6-inch (152-mm) guns mounted by certain cruisers. Battleships, which have occasionally seen service since World War II, have 16-inch (406-mm) guns. Large guns are housed, usually in groups of three, in a turret, a heavily armored, boxlike enclosure. The turret rotates together with all of its below-deck loading and operating machinery.

Smaller guns, those of 5 inches (127 mm) and less, are housed in rotating mounts which are sometimes enclosed in light armor. Mounts contain from one to four guns. Some of these guns, such as the U.S. Navy's 5-inch 54-caliber gun, can be used against both air and surface targets. Most antiaircraft guns load automatically and are fired remotely by a computer.

Missiles have replaced guns for many purposes on naval vessels; some ships, such as the Polaris submarines, are armed only with missiles. (

Mostly all cannon were cast in brass, bronze, or cast iron until post-American Civil War, 1861-1865. Manufacturers would also add more metal to make the barrel walls thicker in order to make the cannon stronger.

In the late 19th century, manufacturers made larger guns by forging, where workers melt the steel in a furnace, then pour it into a gun or ingot mold so that it cools. Then the metal is reheated to about 2100 degrees F (1150 degrees C) and hydraulic hammers or presses are utilized to forge it into shape.

In today’s times, most gun tubes are made by the mono-block method due to the development of high-strength steels. Here the manufacturers increase the strength of the tube by expanding it under internal pressure until the interior diameter of the tube has been permanently enlarged. When the pressure is released, the outer layers of metal tend to shrink to their original dimensions, but the inner layers tend to maintain their enlarged diameter. This results in a compression of the inner layers. Cold working or autofrettage is another name given to this process. The tube is annealed or tempered after it has been formed by being heated and slowly cooled. The next step is for the workers to machine it to its final specifications.

The gun is rifled after final machining. Workers cut grooves in the finished bore surface of the gun. The grooves are not cut directly into the barrel, but sometimes are cut into a separate tube called a liner, which can be inserted into the barrel. A rifled liner can be replaced with a new liner when it becomes worn, but due to the high cost of construction, their use has been limited.