A mortar is a gun firing at a high angle (more than 45°), to perform indirect fire. The curved, bell-shaped trajectory of the projectile makes it possible to reach an objective placed behind an obstacle, which a gun cannot engage because the trajectory of its projectile is tense. The energy produced by the recoil is directly absorbed by the ground or the reinforced platform of a vehicle. The weapon has a short, generally smooth barrel with no rifling. In most cases, it is muzzle loaded, the ammunition being fired by falling on a fixed firing pin. However, the higher calibers and longer barrels have sometimes made it necessary to adopt breech loading for this type of weapon, and therefore the use of a percussion mechanism. Another little used variant of the mortar is the so-called spigot one, where the projectile envelops the launcher then reduced to a simple guide rod.
Born as a siege weapon in the 17th century, the mortar became, during the 20th century, an essential support weapon for the infantry, providing it with the possibility of attacking an entrenched enemy with a piece of equipment. much more mobile and requiring less logistics than conventional artillery.
Siege Mortars
The mortar was born in the 17th century, from the need for artillery capable of firing against hidden targets during a siege. Indeed, the generalization and the increase of the guns, had made evolve/move the works of defense towards thick embankments of ground, unassailable by a ball in tense shooting. We then had the idea of sending a new projectile, the curved shot bomb over the fortifications to reach the defenders, who had been sheltered until then. The projectile arriving slower and less able to rebound, had to be adapted, a hollow body filled with powder and ignited by a rocket was used. The use of the latter requiring a difficult and dangerous double ignition, the projectile then the propellant charge, as well as scholarly calculations for the trajectory, the mortar remained a weapon handled by specialists. In addition, its large caliber and the absence of a wheel on its mounting, made it a piece that was not very mobile and useful only during sieges; to practice masked shooting on the battlefield, an intermediate piece between the cannon and the mortar was invented and used, the howitzer.
The appearance of concrete fortifications at the end of the 19th century led to the appearance of even more powerful siege mortars firing special armor-piercing ammunition to overcome the roof of the casemates. Developed until the Second World War, this type of mortar will eventually disappear during it, for lack of objective requiring its use. The pinnacle will be the German Karl self-propelled mortar with a caliber of 600 millimeters.
The infantry mortar
The modern mortar was born in the mud of the trenches of the First World War, the infantry needed a weapon to reach their opponent in the trench opposite. We are going to develop a series of weapons practicing curved shooting, such as torpedo launchers or grenade launchers. In 1915, Sir Wilfred Stokes developed his trench mortar, literally trench mortar, which became the first modern mortar. Called crapouillot by French soldiers, this weapon and its derivatives were used throughout the war with great success. Indeed its curved trajectory makes it easier to reach the enemy trenches than the artillery which shoots far behind the front. After the war these weapons are improved and will give the mortar as it exists today. It is made dismountable and transportable by small teams and the ammunition is made extremely effective by the use of the percussion fuse, exploding on impact. It was the Brandt company that would set the standard for the infantry mortar, with its two models designed in the 1920s, the 81 mm and the 60 mm.
This new weapon is very mobile because it disassembles into three parts, a base, the tube and the bipod, all three of which can be transported by a man on foot. Its ammunition, the 81 mm shell, is terminated by a finned tail, around which is fixed the propellant charge. It is easy to use:just drop it in the tube and, reaching the bottom, the primer, located at its rear end, is ignited by a fixed firing pin at the bottom of the tube. This principle is simple, the tube has no moving parts that are complicated to manufacture and a trained shooter manages to fire between twenty and twenty-five shells per minute. The pointing and battery operations remain simple and do not require a large number of personnel or specific equipment like conventional artillery pieces, the range is adjusted by tilting the tube more or less with a crank located on a bipod and adding and removing portions of the propellant charge. Observation and adjustment of shooting can be carried out with binoculars. This weapon will quickly impose itself and be adopted or copied in a more or less modified way by most nations. The USSR, for example, chose to use the 82 mm caliber, which had the advantage of being able to use 81 mm ammunition, with a loss of precision, but making the reverse impossible.
The heavy mortar
It is the latter which will develop the approach mortar and during the Second World War, in 1938, it puts into service a heavier model with a caliber of 120 mm, intended for the regimental level. Driven by their lack of conventional artillery, following the terrible losses of the summer of 1941, the Soviets will invent a new way of using the mortar by entrusting it to artillerymen deprived of cannons. Their heavy mortars grouped in regiments, even mortar brigades, comprising 108 pieces, will compensate for the lack of howitzers or guns. In 1943, they released an even more powerful 160 mm model, then after the war a 240 mm, whose one hundred kilogammes shell far exceeded the destructive power of a 155 mm howitzer shell. Even if the use is restricted due to the shorter range, this cheap artillery will be extremely effective in preparing the ground for assault units. It weighs 600 kilograms and can fire from 600m up to 12km.
Self-propelled mortars
During the Second World War, although the mortar was quite mobile, to follow the troops on foot, there appeared the need to provide it with automobile support, in order to be able to follow the nascent mechanized units. The first solution found is to use a simple infantry mortar from a vehicle whose floor has been reinforced, then semi-tracked infantry transport, or even simple trucks, but also old-fashioned tanks are used. where the mortar is installed in the turret well, instead of it. The weapon can then be dismantled and served on the ground outside the vehicle. An imposing model, the Sturmtiger on Panzer VI Tiger chassis will see the light of day.
Thereafter, real self-propelled mortars will appear where the weapon is integrated into the vehicle and can only be served from of this one. One of the pioneering armies in this field will be the Tsahal, which will reuse many heavy tubes of Soviet origin, on chassis like that of the M4 Sherman. The Soviets will follow in their footsteps with models like the 2S4, or the 2S9. Another interesting type is the AMOS, developed by the Finns and Swedes, twin-barrel fires intelligent infrared-guided munitions, to attack tanks from above.
Naval use
Another field of employment, appears during the Second World War, the use against the submarines. Indeed, when attacking a submersible, a ship must at this time navigate above it to use its depth charge ramps, located at the rear. In doing so, he loses the contact maintained thanks to his ASDIC or his sonar. The idea was then born to propel the charges to the front of the building, using mortars. The first test carried out, the Hedgehog, of the Royal Navy will use spigot mortars. Subsequently, a more conventional type of mortar will be used in the Squid and Limbo systems. The Soviets, after having copied the Hedgehog in 1949 by creating the MBU-200, will develop it into the MBU-600, in 1956 which has a more effective range of six hundred meters.