Mortar (weapon)

American soldiers firing a 120 mm mortar

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.

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Function

81 mm high explosive, white phosphorus and illumination mortar rounds

A mortar is relatively simple and easy 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.

These attributes contrast with the mortar's larger siblings; howitzers and field guns, which fire at higher velocities, longer ranges, flatter arcs, and sometimes using direct fire.

In the 19th and early 20th centuries very heavy immobile siege mortars were used, of up to one metre 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.

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. 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 be transported over any terrain and is not burdened by the logistical support needed for artillery.

Heavy mortars are typically between 120-300 mm caliber[1]. 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 heavy mortar can be mounted on a towed carriage, or permanently vehicle-mounted as a self-propelled mortar. Twin-barrelled self-loading mortars — such as the Patria AMOS PT1 — are the latest evolution of these heavy mortars and are mounted on platforms such as armored personnel carriers, tank chassis, and coastal patrol boats.[2]

Design

Most modern mortar systems consist of three main components: a barrel, a base plate, and a bipod.

Modern mortars normally range in caliber from 60mm (2.36 in) to 120mm (4.72 in). However, mortars both larger and smaller than these specifications have been produced. An example of the smaller scale is the British 51 mm Light Mortar which is carried by an individual and consists of only a tube and a base plate. Conversely, a large example is the Soviet 2S4 M1975 Tyulpan (tulip flower) 240mm self-propelled mortar.

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.

Ammunition for mortars generally come in two main varieties: fin-stabilised and spin-stabilised. The former have short fins on their posterior portion which control the path of the shell in flight. Spin-stabilized mortar shells rotate as they travel along and leave the mortar tube. This action stabilizes them in much the same way as a rifle bullet. Both types of rounds can be either illumination (infra-red or visible illumination), smoke, or high explosive.

Spin-stabilised rounds require a rifled barrel. Since mortars generally are muzzle loaded, the mortar shell has a pre-engraved band, called an obturator, that engages with the rifling of the barrel. The increase in accuracy is offset by an increase in loading time and accounting for drift; a peculiarity of rifled systems that causes the round to "drift" perpendicular to the spin axis; this Magnus effect is common to any spinning projectile, and is, for example, what makes it possible for pitchers to throw curve balls.

One of the advantages in the use of mortars is the volume efficiency of their casing. While this doesn't hold true for rifled mortars, the smooth-bore models (as they do not have to withstand the rotational forces placed upon them by rifling) can be designed with much thinner skins, increasing the explosive load they can carry. Due to the difference in available volume a smooth-bore mortar of a given diameter will have a greater explosive yield than a similarly sized artillery shell. An excellent example is the comparison of a 120 mm mortar and a 155 mm artillery shell which have almost identical explosive capabilities.

Mortars come in a variety of calibers. The French 81 mm mortar became standard for many countries. The Soviets took advantage of this by standardising on 82 mm mortars. This allowed troops using Soviet mortars to use mortar ammunition of other countries found on the battlefield, albeit with less accuracy, while their own would be too large for their opponents. This advantage was used during the Vietnam War and at other times.

Georgian-era portable Trench Mortar.

Spigot mortar

Spigot mortars are a particular type of mortar consisting of a mostly solid rod or spigot, and a hollow tube in the projectile into which the spigot fits, inverting the normal tube mortar arrangement. At the top of the tube in the projectile is a cavity containing propellant such as cordite. There is usually a trigger mechanism built into the base of the spigot, with a long firing pin running up the length of the spigot activating a primer inside the projectile and firing the propellant charge.

The advantage of a spigot mortar is that the firing unit (baseplate and spigot) is smaller and lighter than a conventional mortar of equivalent payload and range. It is also somewhat simpler to manufacture.

The disadvantage is that the mortar projectile requires additional material to contain the propellant gases during firing. While most mortar shells have a streamlined shape towards the back that naturally fits a spigot mortar application well, using that space for the spigot mortar tube takes volume and mass away from the explosive warhead payload and fragmentation mass of the projectile. If a soldier is carrying only a few projectiles, the projectile weight disadvantage is not significant. However, the weight of a large quantity of the heavier and more complex spigot projectiles offsets the weight saved due to the spigot mortar being lighter than a conventional mortar.

A near silent mortar can be made using the spigot principle. Each round has a closely fit but moveable plug in the tube that fits over the spigot. When the round is fired, the projectile is pushed off the spigot, but before the plug clears the spigot, the plug is caught by a narrowing at the base of the tube. This traps the gases from the propelling charge and hence the sound of the firing. Post World War II the silent Belgium Fly-K spigot mortar was accepted into French service as the TN-8111.

Spigot mortars are generally out of favor in modern usage, replaced by small conventional mortars.

Mallet's Mortar with 36 inch shells which would have contained 480lb (217kg) of gunpowder.
A 1377 made chinese Bombard
Mortar of the Knights of Saint John of Jerusalem, Rhodes, 1480-1500, fired 260 kg cannon balls.
An 1832 "Monster Mortar" invented by Henri-Joseph Paixhans.
19th century mortar, facing the sea, in the walls of Acre.

Military applications of spigot mortars include

Nonmilitary applications include use of small-caliber spigot mortars to launch lightweight, low-velocity foam dummy targets used for training retriever dogs for bird hunting. Extremely simple launchers use a separate small primer cap as the sole propellant (similar or identical to the cartridges used in industrial nailguns).

Other advantages

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. For example, conventional long-range artillery could not shell a target 1 km away and at an elevation disadvantage of 30 metres (100 ft), but shelling the target by mortar would be easy.

History

Mortars have existed for hundreds of years, first seeing use in siege warfare. However, the early incarnations of these weapons were large and heavy, and could not be easily transported. Simply made, these weapons were no more than iron bowls reminiscent of the kitchen and apothecary mortars from where they drew their name.

An early transportable mortar was invented by Baron Menno van Coehoorn (Siege of Grave, 1673[3]). Coehorn-type mortars of approximately 180 pounds (82 kg) weight were used by both sides during the American Civil War.

During the Russo-Japanese War, Leonid Gobyato for the first time applied deflection from closed firing positions in the field and with General Roman Kondratenko designed the first mortar that fired navy shells. However, it was not until the Stokes trench mortar devised by Sir Wilfred Stokes in 1915, that the modern mortar transportable by one person was born. The Germans also developed a series of trench mortars or Minenwerfer in calibers from 7.58cm to 25cm during World War I, though these were rifled.

Extremely useful in the muddy trenches of the Western Front, mortars were praised because of the shell's high angle of flight; a mortar round could be aimed to fall directly into trenches where artillery shells, due to their low angle of flight, could not possibly go. Modern mortars have improved upon these designs, offering a weapon that is light, adaptable, easy to operate, and yet possesses enough accuracy and firepower to provide the infantry with quality close fire support against soft and hard targets more quickly than any other means.

Largest mortars

The largest mortars ever developed were the French "Monster Mortar" (36 french inches; 975 mm; developed by Henri-Joseph Paixhans in 1832), "Mallet's mortar" (36 inches; 910 mm; developed at the Woolwich Arsenal, London, in 1857) and the "Little David" (36 inches; 910 mm; developed in the United States for use in World War II). All three mortars had a caliber of 36 inches, but only the "Monster Mortar" was used in action (at the Battle of Antwerp in 1832).[4]

Improvised mortars

Improvised, or "homemade", mortars have been used by insurgent groups, usually to attack fortified military installations. Some of the best examples were those used by the Provisional Irish Republican Army during the 1970s, 1980s and 1990s. These were known as "barracks busters" and were usually constructed from heavy steel piping of 3-4 inches in diameter mounted on a steel frame. This could be constructed easily inside a van such as the MK 1 Ford Transit. Bombs were also home-made and had simple propellant fuses.

The mortars were usually deployed as a battery of four or six welded onto the same steel frame. 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 short delay. This allowed the mortar gunner to escape even before the mortar is fired.

A famous use of this weapon was an IRA assassination attempt on 7 February 1991. The terrorists mortared 10 Downing Street as a Cabinet meeting was in session. However the bomb landed in the back garden of the British Prime Minister's residence and only shattered the rear windows. Prime Minister John Major was forced to move to Admiralty House while repairs were effected.[5]

Currently, mortars are used by Palestinian guerrillas in the Gaza Strip against Israeli targets, including towns in Israel near the border with Gaza. A partial list of these attacks can be found in the List of Qassam rocket attacks article.

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See also

Citations and notes

  1. ↑ Vesa Toivonen, 2003, From Tampella to Patria, 70 Years of Finnish Heavy Weapons Production, Tampere, ISBN 952-5026-26-4
  2. ↑ Toivonen, 2003
  3. ↑ BARON VAN MENNO COEHOO... - Online Information article about BARON VAN MENNO COEHOO
  4. ↑ "Largest Mortar". Guinness World Records. Retrieved on 2006-04-04.
  5. ↑ http://www.keesings.com/search?kssp_a_id=38019n03uki&kssp_selected_tab=article Mortar attack on 10 Downing Street

Recommended reading

External links