MORTAR AND BOMBS

A mortar is an indirect fire weapon that fires shells at low velocities, short ranges, and high-arcing ballistic trajectories. It is typically muzzle-loading and has a barrel length less than 15 times its caliber.

A mortar is relatively simple and easy to operate. A modern mortar consists of a tube into which gunners drop a shell, which is usually referred to as a bomb. The shell contains a quantity of propellant. When it reaches the base of the tube it hits a firing pin, which detonates the propellant and fires the shell. Some larger caliber mortars have a string operated firing pin instead of a fixed one. The tube is generally set at between 45 and 85 degrees angle to the ground, with the higher angle giving shorter firing distances.

From the 18th to the early 20th century very heavy, relatively immobile siege mortars were used, of up to one metre calibre, often made of cast iron and with outside barrel diameter many times that of the bore diameter. Smaller and more portable designs were introduced during the First World War, primarily for trench warfare, which took place at relatively close ranges. Mortars continue to be in use to the present day.

Light and medium mortars are portable, and usually used by infantry units. The chief advantage a mortar section has over an artillery battery is the flexibility of small numbers, mobility and the ability to engage targets in the defilade with plunging fires. Mortars are 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 be transported over any terrain and is not burdened by the logistical support needed for artillery.

Heavy mortars are typically between 120- and 300-mm caliber. These weapons 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 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. Heavy mortars can be mounted on a towed carriage, or permanently vehicle-mounted as a self-propelled mortar.

Improvised, mortars have been used by insurgent groups, usually to attack fortified military installations. As each tube fired only one round, mortars were usually deployed as a battery of four or six welded onto a steel frame. This was often concealed inside a van such as a Ford Transit. The idea was that the improvised propellant fuses could be set once the mortar carrier was aimed roughly at the target and the mortars would automatically fire after a delay – this allowed the mortar gunner time to escape before the rounds were fired. After firing, a timer-operated incendiary device could set the vehicle on fire in order to destroy any forensic evidence it contained.