A mortar is a smoothbore, muzzle-loading artillery piece that fires indirect shells (bombs in the UK) at low velocities, short ranges, and high-arcing ballistic trajectories. These attributes contrast with the mortar`s larger siblings, rifled howitzers and field guns, which fire at higher velocities, longer ranges, and flatter arcs. Typically a modern mortar consists of a tube into which is dropped a mortar shell (bomb) onto a firing pin resulting in the detonation of the propellant and the firing of the shell.
In the 19th and early 20th centuries very heavy immobile siege mortars were used, of up to 1 m calibre.
A mortar can also be a launcher for fireworks, a hand-held or vehicle-mounted projector for smoke shells or flares, or a large grenade launcher.
Mortars are relatively simple and easy to operate artillery pieces. Light and medium mortars are man-portable, and are usually used by infantry organizations. The chief advantage a mortar section has over an artillery battery is its small size and its mobility. It is able to fire from the protection of a trench or defilade. In these aspects the mortar is an excellent infantry support weapon, as it can travel over any terrain and is not burdened by the logistical support needed for artillery.
There are also heavy mortars of 120 mm to 240 mm calibre. These are usually towed or vehicle-mounted weapons, sometimes breech-loaded, and normally employed by artillery units attached to battalion through division level. Even at this large size, mortars are simpler and less expensive than comparable howitzers or field guns.
A mortar can be carried by one or more people (larger mortars can 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 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.
An unusual support weapon is the Soviet/Russian 2B9 Vasilek 82 mm automatic mortar, also manufactured by the People`s Republic of China`s Norinco as the Type W99 mortar. This is a fully-automatic weapon, capable of a high rate of fire. It can also be used in a direct fire mode, and can fire a HEAT round for use against light armoured vehicles. Another interesting recent development is the emergence of the Lacroix Defense`s Samourai Urban Warfare Weapon, described as a man-portable, shoulder-fired mortar.