A mortar is a muzzle-loading indirect fire weapon that fires shells at low velocities, short ranges, and high-arcing ballistic trajectories. It typically has a barrel length less than 15 times its caliber. This trajectory allows the shells to travel over obstacles to hit a target. Shells are loaded through the muzzle into a short barrel. They carry a charge that propels them from the barrel of the mortar. Mortars are particularly suited to warfare in difficult terrain. They are easily transported and simple to operate.
A modern mortar consists of a tube into which gunners drop a shell. A firing pin at the base of the tube detonates the propellant and fires the shell.
Light and medium mortars are portable, and usually used by infantry units. The mortar is an excellent infantry support weapon, as it can be transported over any terrain and is not burdened by the logistical support needed for artillery.
Heavy mortars are usually towed or vehicle-mounted, sometimes breech-loaded, and normally employed by infantry units attached to battalion through division level. Even at this size, mortars are simpler and less expensive than comparable howitzers or field guns.
A mortar can be carried by one or more men (larger mortars can usually be broken down into components), or transported in a vehicle. An infantry mortar can usually also be mounted and fired from a mortar-carrier; a purpose-built or modified armoured vehicle with a large roof hatch.
A heavy mortar can be mounted on a towed carriage, or permanently vehicle-mounted as a self-propelled mortar. Twin-barrelled self-loading mortars are the latest evolution of these heavy mortars and are mounted on platforms such as armored personnel carriers, tank chassis, and coastal patrol boats.
Most modern mortar systems consist of three main components: a barrel, a base plate, and a bipod. Modern mortars normally range in caliber from 60 mm to 120 mm. Smaller mortars (up to 81 mm) are commonly used and transported by infantry based mortar sections as a substitute for, or in addition to, artillery.
An additional advantage of the mortar is its ability to drop shells on targets close to the mortar, due to the lobbing nature of the ballistics. This feature also makes it possible to launch attacks from positions lower than the target of the attack. Mortars are also very effective behind relatively concealed positions, such as the natural escarpments on hillsides or from woods, especially if observers are being employed in strategic positions to direct fire.