Mortar (weapon)

Wilfred Stokes with example of his WWI mortar and bombs.

It was not until the Stokes Mortar was devised by Sir Wilfred Stokes in 1915 during the First World War that the modern mortar transportable by one person was born. In the conditions of trench warfare, there was a great need for a versatile and easily portable weapon that could be manned by troops under cover in the trenches. Stokes's design was initially rejected in June 1915 because it was unable to use existing stocks of British mortar ammunition, and it took the intervention of David Lloyd George (at that time Minister of Munitions) and Lieutenant-Colonel J. C. Matheson of the Trench Warfare Supply Department (who reported to Lloyd George) to expedite manufacture of the Stokes mortar. The weapon proved to be extremely useful in the muddy trenches of the Western Front, as 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.[10]

The Stokes mortar was a simple muzzle-loaded weapon, consisting of a smoothbore metal tube fixed to a base plate (to absorb recoil) with a lightweight bipod mount. When a mortar bomb was dropped into the tube, an impact sensitive primer in the base of the bomb would make contact with a firing pin at the base of the tube, and detonate, firing the bomb towards the target. It could fire as many as 25 bombs per minute and had a maximum range of 800 yards (730 m) firing the original cylindrical unstabilised projectile.[11]

A modified version of the mortar, which fired a modern fin-stabilised streamlined projectile and had a booster charge for longer range, was developed after World War I;[12] this was in effect a new weapon. By World War II, it could fire as many as 30 bombs per minute, and had a range of over 2,500 yards (2,300 m) with some shell types.[13]

The French developed an improved version of the Stokes mortar as the Brandt Mle 27, further refined as the Brandt Mle 31; this design was widely copied with and without license.[14][15][16]

These weapons were the prototypes for all subsequent light mortar developments around the world.

The German 60 cm Karl-Gerät heavy siege mortar in August 1944

Interior of an IDF M113 mortar carrier showing the placement of an 81 mm mortar

Mortar carriers are vehicles which carry a mortar as a primary weapon. Numerous vehicles have been used to mount mortars, from improvised civilian trucks used by insurgents, to modified Infantry fighting vehicles, such as variants of the M3 half track and M113 armored personnel carrier, to vehicles specifically intended to carry a mortar. Simpler vehicles carry a standard infantry mortar while in more complex vehicles the mortar is fully integrated into the vehicle and cannot be dismounted from the vehicle. Mortar carriers cannot be fired while on the move and some must be dismounted to fire.

There are numerous AFVs and even MBTs that can be equipped with a mortar, either outside or inside of the cabin. The Israeli Merkava tank uses a 60 mm mortar as a secondary armament. The Russian army uses the 2S4 Tyulpan (Tulip) self-propelled 240 mm heavy mortar which is one of the largest mortars in current use.

2B9 Vasilek 82 mm gun mortar

Gun-mortars are breech-loaded mortars usually equipped with a hydraulic recoil mechanism, and sometimes equipped with an autoloader. They are usually mounted on an armored vehicle and are capable of direct fire. The archetypes are the Brandt Mle CM60A1 and Brandt 60 mm LR, which combine features of modern infantry mortars together with those of modern cannon. Such weapons are most commonly smoothbore, firing fin-stabilised rounds, using relatively small propellant charges in comparison to projectile weight. They have short barrels in comparison to guns and are much more lightly built than guns of a similar calibre – all characteristics of infantry mortars. This produces a hybrid weapon capable of engaging area targets with indirect high-angle fire, and also specific targets such as vehicles and bunkers with direct fire. Such hybrids are much heavier and more complicated than infantry mortars, superior to rocket-propelled grenades in the anti-armour and bunker-busting role, but have a reduced range compared to modern gun-howitzers and inferior anti-tank capability compared to modern anti-tank guided weapons. However, they do have a niche in, for example, providing a multi-role anti-personnel, anti-armour capability in light mobile formations. Such systems, like the Soviet 120 mm 2S9 Nona, are mostly self-propelled (although a towed variant exists). The AMOS (Advanced Mortar System) is an example of an even more advanced gun mortar system. It uses a 120 mm automatic twin-barrelled, breech-loaded mortar turret, which can be mounted on a variety of armored vehicles and attack boats.

A modern example of a gun-mortar is the 2B9 Vasilek.

A Blacker Bombard during training

Spigot mortars, a particular type of mortar, consist mainly of a solid rod or spigot, onto which a hollow tube in the projectile fits—inverting the normal tube-mortar arrangement. At the top of the tube in the projectile, a cavity contains 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 tube mortar of equivalent payload and range. It is also somewhat simpler to manufacture. Further, most spigot mortars have no barrel in the conventional sense, which means ammunition of almost any weight and diameter can be fired from the same mortar.

The disadvantage is that while most mortar bombs have a streamlined shape towards the back that fits a spigot mortar application well, using that space for the spigot mortar tube takes volume and mass away from the payload 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 operate using the spigot principle. Each round has a close-fitting sliding 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 it is caught by a constriction at the base of the tube. This traps the gases from the propelling charge and hence the sound of the firing. After World War II the Belgium Fly-K silent spigot mortar was accepted into French service as the TN-8111.

A hedgehog launcher on display. Note the exposed spigot on the lower left launcher

Spigot mortars are generally out of favor in modern usage, replaced by small conventional mortars. Military applications of spigot mortars include:

• The 290 mm petard mortar used on the Churchill AVRE by Britain in World War II.[17]
• The 320 mm Type 98 mortar used by Japan in World War II to some psychological effect in the battles of Iwo Jima and Okinawa
• Anti-tank launchers
  • The Blacker Bombard and PIAT anti-tank launcher used by Britain in World War II utilised a spigot mortar type of launcher.
• Anti-submarine launchers
  • The Hedgehog launcher, used from the deck of a ship, used 24 spigot mortars which fired a diamond pattern of anti-submarine projectiles into the sea ahead of the ship. A sinking projectile detonated if it struck a submarine, and the pattern was such that any submarine partly in the landing zone of the projectiles would be struck one or more times.

Non-military applications include the use of small-calibre 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 nail guns).

Improvised mortars in Batey ha-Osef Museum, Tel Aviv, Israel.

Improvised, or "home-made", mortars have been used by insurgent groups, usually to attack fortified military installations or to terrorize civilians. They are usually constructed from heavy steel piping mounted on a steel frame. These weapons may fire standard mortar rounds, purpose made shells, re-purposed gas cylinders filled with explosives and shrapnel, or any other type of improvised explosive, incendiary or chemical munitions. These were called "Barrack Busters" by the Provisional Irish Republican Army (IRA). They are known as "Hell Cannons" in the Syrian Civil War, where observers have noted that they are "wildly inaccurate" and responsible for hundreds of civilian deaths.[18]

L16 mortar tube, base plate and bipod

Looking down an L16 mortar tube. Note: fixed firing pin

Most modern mortar systems consist of four main components: a barrel, a base plate, a bipod and a sight. Modern mortars normally range in calibre from 60 mm (2.36 in) to 120 mm (4.72 in). However, both larger and smaller mortars have been produced.

The modern mortar is a muzzle-loaded weapon and relatively simple and easy to operate. It consists of a tube into which the gunners drop a mortar round. When the round reaches the base of the tube it hits a fixed firing pin that fires the round. The tube is generally set at an angle of between 45 and 85 degrees to the ground, with the higher angle producing a shorter horizontal round trajectory. Some mortars have a moving firing pin, operated by a lanyard or trigger mechanism.

Ammunition for mortars generally comes in two main varieties: fin-stabilized and spin-stabilized. Examples of the former have short fins on their posterior portion, which control the path of the bomb in flight. Spin-stabilized mortar bombs rotate as they travel along and leave the mortar tube, which 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, high explosive and training rounds. Mortar bombs are often referred to, incorrectly, as "mortars".[19]

Operators may fire spin-stabilized rounds from either a smoothbore or a rifled barrel. Rifled-mortars are more accurate, but slower to load. Since mortars are generally muzzle-loaded, mortar bombs for rifled barrels usually have a pre-engraved band, called an obturator, that engages with the rifling of the barrel. Exceptions to this were the U.S. M2 4.2 inch mortar and M30 mortar, whose ammunition had a sub-caliber expandable ring that enlarged when fired. This allows the projectile to slide down the barrel freely, but grip the rifling when fired. The system resembles the Minié ball for muzzle-loading rifles. For extra range, propellant rings (augmentation charges) are attached to the bomb's fins. The rings are usually easy to remove, because they have a major influence on the speed and thus the range of the bomb. Some mortar rounds can be fired without any augmentation charges, e.g., the 81 mm L16 mortar.

Soldiers standing in front of an M1064 mortar carrier, holding a XM395 Precision Guided Mortar Munition prototype at Fort Benning, Ga., Feb 2006

The XM395 Precision Guided Mortar Munition (PGMM) is a 120 mm guided mortar round developed by Alliant Techsystems.[21] Based on Orbital ATK's Precision Guidance Kit for 155 mm artillery projectiles, XM395 combines GPS guidance and directional control surfaces into a package that replaces standard fuzes, transforming existing 120 mm mortar bodies into precision-guided munitions.[22] The XM395 munition consists of a GPS-guided kit fitted to standard 120 mm smoothbore mortar rounds that includes the fitting of a nose and tail subsystem containing the maneuvering parts.[23][24]

The Strix mortar round is a Swedish endphase-guided projectile fired from a 120 mm mortar currently manufactured by Saab Bofors Dynamics. STRIX is fired like a conventional mortar round. The round contains an infrared imaging sensor that it uses to guide itself onto any tank or armoured fighting vehicle in the vicinity where it lands. The seeker is designed to ignore targets that are already burning. Launched from any 120 mm mortar, Strix has a normal range of up to 4.5 km. The addition of a special sustainer motor increases the range to 7.5 km.

The GMM 120 (Guided Mortar Munition 120; known as Patzmi; also referred to as Morty) is a GPS and/or laser-guided mortar munition, which was developed by Israel Military Industries.[25][26] The Russian KM-8 Gran is also laser-guided.[27]