Artillery includes guns, howitzers, mortars, and missile launchers.
Fixed ammunition, made like the cartridges for small arms, is used in some guns with bore diameters up to 105 millimeters (about 4 inches). In semifixed ammunition, used in some guns of calibers from 75 mm to 120 mm (about 5 inches) and in some 5-inch (127-mm) and 6-inch (152-mm) naval guns, the projectile fits loosely in the case and can be removed to increase or decrease the powder charge. With separate-loading ammunition the projectile is placed in the gun, followed either by a case containing propellant and primer, or by cloth bags of powder and a separate primer.
An artillery projectile made of solid metal is called shot. Several types, known as kinetic-energy projectiles, are designed for penetrating armor plate. These projectiles are made of a dense metal (or with a core of dense metal) and are fired from guns at a very high velocity. Field artillery projectiles range in size from tens of millimeters to a few hundred millimeters, and can weigh from a few pounds (1 kilogram) to hundreds of pounds (hundreds of kilograms).
An artillery projectile that contains an explosive charge is called a shell. A highexplosive shell inflicts damage by the force of the explosion itself, as well as by fragments of the shell casing that scatter widely. One type of projectile designed for use against troops contains bundles of small dartlike fragments called flechettes that scatter in all directions with great force when the shell explodes. Smoke shells contain a chemical used to produce smoke screens. Chemical shells, used in World War I, contained poison gas that was released on impact. Illuminating, or star, shells contain flares attached to parachutes to illuminate targets at night.
Armor-piercing shells are designed primarily for use against tanks. Some, called kinetic-energy shells, use high velocity to penetrate the armor; others, called HEAT shells, use explosives to do so. Armorpiercing incendiary shells are designed to set fires inside tanks. Submunition shells, used mainly against troops, contain explosive devices (usually grenades or mines) that are ejected when the shell lands.
The explosive charge in an artillery projectile is usually TNT, amatol, a picric-acid compound, or ammonium picrate.
The explosive charge is set off by a fuze. The rotation of the projectile in the gun barrel unlocks the fuze mechanism so that it is “armed” and ready to set off the main charge. The fuze may act directly on the main charge, or, more generally, it may detonate a small quantity of another explosive, such as lead azide. A series of two to four successive split-second explosions (called the explosive train) takes place in the firing of many types of rounds.
Impact fuzes are designed to detonate the projectile on striking an object. Some fuzes contain a short delay element (normally compressed black powder) which allows the shell either to penetrate the target or to ricochet into the air for a fraction of a second before bursting. Time fuzes explode the shell at a preset time after it leaves the gun. Some time fuzes use a mechanical watchlike device; others are operated by the slow burning of a train of compressed black powder. The proximity fuze contains an electronic device that explodes the projectile at a preset distance from the target. Other types of fuzes may be set to detonate the explosive charge at a given altitude.
Artillery is fired by friction primers, in which a strip of metal is drawn through mercury fulminate or some other priming material; by electric primers, ignited by a spark; and by percussion primers like those used on small-arms ammunition. The propellant is usually a slow-burning smokeless powder. Smokeless powders are forms of nitrated cellulose.
The ammunition used in recoilless rifles has a perforated case to allow part of the propellant gases to escape to the rear of the gun, thus eliminating recoil, or “kick.”