A mortar is a high-trajectory fire weapon in which the recoil force is passed directly to the ground by means of a base plate. The conventional mortar, as used by the armies of most countries, is muzzle loading and has a smooth bore. It fires a fin-stabilized projectile at subsonic velocity and establishes zones of fire by variation of the charge weight. Range is adjusted by altering the elevation. The high trajectory of a mortar allows the weapon to be placed behind hills, in valleys, or in small steep-sided pits and to engage troops in trenches, sunken roads, or behind cover.
The mortar was one of the earliest forms of artillery and is known to have been used by Mohammed II at the time of the siege of Constantinople in 1453. Known in Europe as the bombard, it consisted of a metal pot secured to a timber base. It was used for attacking fortresses and cities under siege and also for action against ships close to shore. There was also a naval equivalent. The bombard fell out of favor as other forms of artillery developed and did not come into prominence again until World War I, when a British inventor, Sir Wilfred Stokes, produced a mortar 3 in. (76 mm) in diameter, a caliber that is still in favor today. Probably the largest mortar ever produced was the Little David mortar, which was built in 1944 for the U.S. Army. It had a 36 in. (914 mm) caliber and fired a massive projectile weighing 3,700 lbs. (1,678 kg).
Construction
The great majority of mortars have four main parts: the barrel, the base plate, the mount, and the sight. The barrel is a smooth-bore steel tube, and the exterior is also usually smooth, although some mortars incorporate radial finning to assist cooling. The firing mechanism is incorporated in a breech piece, which is usually screwed into the base of the barrel. In many cases, the firing mechanism is a simple stud, which sets off the propellant charge of the mortar bomb by impact as soon as the latter has fallen to the lower end of the barrel after loading. In some mortars, however, the firing mechanism is a spring-operated device controlled by an external trigger. The base plate is designed to distribute the downward force of the propellant explosion over as large an area as possible to prevent the mortar from being driven downward into the ground. The mounting is normally a bipod, but occasionally, a tripod is used. The mounting supports the barrel and carries the elevating and traversing mechanisms, which are used for aiming. In many mortars, a shock absorber is incorporated in the mounting; it usually consists of one or two cylinders containing springs, although in some heavier mortars a hydraulic system may be employed. These cylinders are interposed between the barrel collar and the bipod, and after the barrel has recoiled and been pushed back by the reaction of the baseplate, the springs ensure that the barrel returns.
The bipod carries a cross-leveling device that enables the sights to be kept upright regardless of the slope of the ground on which the mortar is situated. Mortar sights have increased in complexity as the years have passed. Initially, they were very simple and consisted of an aiming tube and a flat plate, which allowed the gunner to relate the direction in which the mortar was pointing to some arbitrarily selected reference point. The modern mortar sight allows the target bearing to be determined and also allows the range and bearing to be recorded so that once a target has been attacked, it can be reengaged without going through the entire process again.
In today’s armies, handheld computers give the mortar an impressive ability to hit a target after a single ranging shot. Speed has become of great importance, as modern mortar-locating radars can detect a mortar’s position after a few rounds, so it can then be put under attack itself.
