A mortar today is usually a simple, lightweight, man-portable, Muzzleloader cannon, consisting of a Smoothbore (although some models use a Rifling) metal tube fixed to a base plate (to spread out the recoil) with a lightweight bipod mount and a sight. Mortars are typically used as indirect fire weapons for close fire support with a variety of ammunition. Historically mortars were heavy Siege. Mortars launch explosive shells (technically called Bomb) in high arching ballistic trajectories.
The first use in Siege was at the 1453 siege of Constantinople by Mehmed the Conqueror. An Italian account of the 1456 siege of Belgrade by Giovanni da Tagliacozzo states that the Ottoman Turks used seven mortars that fired "stone shots one Italian mile high". The time of flight of these was apparently long enough that casualties could be avoided by posting observers to give warning of their trajectories.
Early mortars, such as the Pumhart von Steyr, 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 whence they drew their name. An early transportable mortar was invented by Baron Menno van Coehoorn in 1701.
The mortar had fallen out of general use in Europe by the Napoleonic era, although were widely used on the coast to launch lines to ships in distress, and interest in their use as a weapon was not revived until the beginning of the 20th century. Mortars were heavily used by both sides during the American Civil War. At the Siege of Vicksburg, General Ulysses S. Grant reported making mortars "by taking logs of the toughest wood that could be found, boring them out for shells and binding them with strong iron bands. These answered as Coehorn, and shells were successfully thrown from them into the trenches of the enemy". Personal Memoirs of Ulysses S Grant, by Sam Grant, Kindle location 12783,
During the Russo-Japanese War, Lieutenant General Leonid Gobyato of the Imperial Russian Army applied the principles of indirect fire from closed firing positions in the field; and with the collaboration of General Roman Kondratenko, he designed the first mortar that fired navy shells.
The German Army studied the Siege of Port Arthur, where heavy artillery had been unable to destroy defensive structures like barbed wire and Bunker. Consequently, they developed a short-barrelled rifled muzzle-loading mortar called the Minenwerfer. Heavily used during World War I, they were made in three sizes: .
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. The Stokes mortar could fire as many as 25 bombs per minute and had a maximum range of , firing the original cylindrical unstabilised projectile.
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;Ruffell 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 with some shell types.War Dept. Technical Manual TM9-2005, Volume 3, Ordnance Materiel – General, Page 17, December 1942 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. These weapons were the prototypes for all subsequent light mortar developments around the world.
There are numerous armoured fighting vehicles and even main battle tanks that can be equipped with a mortar, either outside or inside of the cabin. The Israeli Merkava tank uses a mortar as a secondary armament. The Russian army uses the 2S4 Tyulpan self-propelled heavy mortar which is one of the largest mortars in current use.
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.
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 caseless underbarrel spigot launcher, the Battelle Pogojet has been developed by Armor Development Group.
Spigot mortars generally fell out of favour after World War II and were replaced by smaller conventional mortars. Military applications of spigot mortars include:
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. Simple launchers use a separate small primer cap as the sole propellant (similar or identical to the cartridges used in industrial ).
The Pasilan 2000, the improved version, has been developed with characteristics similar to a rocket launcher. The Pasilan 2000 was a heavy mortar fired from a mobile launcher mounted on a tractor. The shell does not emit constant muzzle flares like artillery or MBRL. This is ideal for LTTE's camouflage and conceals attacking style. Once a round is fired, forward observers/spies/civilian spotters can correct the fire. The way the tube is installed is similar to the positioning of rocket pods. The length and calibre of the barrel indicate Pasilan 2000 system has common features to the Chinese made Type 82 30-tube MLRS (introduced by the Palestinian Liberation Army (PLA) in the early 1980s) rather than rail-guided Katyusha variants such as the Qassam Rocket. The warhead weight is and it is filled with TNT. It had a range of . The rocket has since then undergone some modifications. The Pasilan 2000 was more lethal than Baba mortar. But it was not heavily used for ground attacks during the Eelam War IV.
Operators may fire spin-stabilised 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 are the US M2 mortar and M30 mortar, whose ammunition has a sub-calibre 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.
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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 . The addition of a special sustainer motor increases the range to .
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 IMI Systems. Another Israeli guided mortar is Iron Sting, developed by Elbit. The Russian KM-8 Gran is also laser-guided.
Mortars are short-range weapons and often more effective than long range artillery for many purposes within their shorter range. In particular, because of its high, parabolic trajectory with a near vertical descent, the mortar can land bombs on nearby targets, including those behind obstacles or in , such as light vehicles behind hills or structures, or infantry in or . This also makes it possible to launch attacks from positions lower than the target of the attack. (For example, long-range artillery could not shell a target away and higher, a target easily accessible to a mortar.)
In trench warfare, mortars can use plunging fire directly into the enemy , which is very hard or impossible to accomplish with long range artillery because of its much flatter trajectory. Mortars are also highly effective when used from concealed positions, such as the natural escarpments on hillsides or from woods, especially if forward observers are being employed in strategic positions to direct fire, an arrangement where the mortar is in relatively close proximity both to its forward observer and its target, allowing for fire to be quickly and accurately delivered with lethal effect. Mortars suffer from instability when used on snow or soft ground, because the recoil pushes them into the ground or snow unevenly. A Raschen bag addresses this problem.
Fin-stabilised mortar bombs do not have to withstand the torque placed upon them by rifling or greater pressures, and can therefore carry a higher payload in a thinner skin than rifled artillery ammunition. Because of 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 of a gun or howitzer. For example, a mortar bomb has approximately the same explosive capability as a artillery shell. Also, fin-stabilised munitions fired from a smooth-bore, which do not rely on the spin imparted by a rifled bore for greater accuracy, do not have the drawback of veering in the direction of the spin.
The largest mortars ever developed were the Belgian "Monster Mortar" () developed by Henri-Joseph Paixhans in 1832, Mallet's Mortar () developed by Robert Mallet in 1857, and the "Little David" (910 mm) developed in the United States for use in World War II. Although the latter two had a calibre of 910 mm, only the "Monster Mortar" was used in combat (at the Battle of Antwerp in 1832). The World War II German Karl-Gerät was a mortar and the largest to see combat in modern warfare.
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