A mortar is an indirect fire weapon that fires explosive projectiles known as bombs at low
velocities, short ranges, and high-arcing ballistic trajectories. It is typically muzzle-loading
with short barrel, generally less than 15 times its caliber.
History Origins
Mortars have existed for hundreds of years, first seeing use in siege warfare. Many historians
consider the first mortars to have been used at the 1453 siege of Constantinople by Fatih
Sultan Mehmed. A European account of the 1456 siege of Belgrade by Giovanni da Tagliacozzo
credits the Ottoman Turks for using seven mortars that fired "stone shots one Italian
mile high". The speed of these was apparently slow enough that casualties could be avoided
by posting observers that gave warning of their trajectories.
Early mortars, such as the Pumhart von Steyr, were also 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. An early use of these more mobile mortars
as field weapons was by British forces in the suppression of the 1719 Jacobite rising
at the Battle of Glen Shiel. Wide angle trajectory mortars held a great advantage over standard
field guns in the rough terrain of the West Highlands in Scotland.
Coehorn-type mortars of approximately 180 pounds weight were used by both sides during
the American Civil War. At the Siege of Vicksburg, General US Grant reported making such mortars
"by taking logs of the toughest wood that could be found, boring them out for six or
twelve-pound shells and binding them with stong iron bands. These answered as coehorns,
and shells were successfully thrown from them into the trenches of the enemy."
The mortar had fallen out of general use by the Napoleonic era and interest in the weapon
was only revived at the beginning of the 20th century. 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 bunkers. The solution they developed
was a short-barrelled rifled muzzle-loading mortar called the minenwerfer, and was built
in three sizes. Recognizing the advantages of the minenwerfer in trench warfare, production
was stepped up and, by 1918, the numbers had increased dramatically to 1,234 heavy, 2,361
medium and 12,329 light minenwerfer. Modern portable mortar
It was not until the Stokes trench mortar 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 undercover 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 and Lieutenant-Colonel J. C. Matheson
of the Trench Warfare Supply Department 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.
The Stokes mortar was a simple weapon, consisting of a smoothbore metal tube fixed to a base
plate 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 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; 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 2500 yards with some shell types.
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.
About 700 Stokes mortars were acquired by Poland between 1923 and 1926. These weapons
were the prototype for all subsequent light mortar development around the world.
Mortars today, while substantially similar in design to the Stokes mortar,are greatly
improved versions; these offer 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", Mallet's Mortar and
the "Little David". All three mortars had a caliber of 36 "inches",
but only the "Monster Mortar" saw action. Improvised mortars
Improvised, or "home-made", mortars have been used by insurgent groups, usually to attack
fortified military installations or to terrorize civilians. The Provisional Irish Republican
Army used some of the best-known examples during the 1970s, 1980s and 1990s. The largest
types came to be known as "barracks busters" and were usually constructed from heavy steel
piping mounted on a steel frame. The largest had a calibre of 320 millimetres and fired
home-made rounds carrying from 80 to 100 kilograms of explosive.
As each tube fired only one round, mortars were usually deployed as a battery of four
or six welded onto a steel frame. This was often concealed inside a van such as a Ford
Transit. The vehicle would be parked, pointing roughly at the target. A timer fired the propellant
charges after a delay – this allowed the mortar gunner time to escape. After firing,
a timer-operated incendiary device could set the vehicle on fire in order to destroy any
forensic evidence it contained. Well-known incidents using these weapons include
the 1985 Newry mortar attack, when nine members of the Royal Ulster Constabulary were killed,
and the Downing Street mortar attack in 1991. The IRA mortared 10 Downing Street as a Cabinet
meeting was in session. Three bombs were launched of which one detonated. It landed in the back
garden of the British Prime Minister's residence and shattered the rear windows. Prime Minister
John Major had to move to Admiralty House while repairs were effected.
Function
The mortar is a relatively simple and easy weapon to operate. A modern mortar consists
of a tube into which assistant gunners drop a purpose-designed bomb. The tube is generally
set at between 45 and 85 degrees angle to the ground, with the higher angle giving shorter
firing distances. The bomb has a small baseline charge and no cartridge case; for extra range
propellant rings are attached to the bomb's fins. When it reaches the base of the tube
it hits a fixed firing pin, which detonates the baseline charge and fires the projectile.
Some mortars have a moving firing pin, operated by a lanyard; others may be fired by a trigger.
These attributes contrast with the mortar's larger siblings, howitzers and field guns,
that fire shells at higher velocities, longer ranges, flatter arcs, sometimes using direct
fire. These weapons are also breech-loaded, while most mortars are muzzle-loaded.
From the 17th to the early 20th century very heavy, relatively immobile siege mortars were
used, of up to one metre calibre, often made of cast iron and with outside barrel diameter
many times that of the bore diameter. An early example was Roaring Meg used during The English
Civil War. Smaller and more portable designs were introduced during the First World War,
primarily for trench warfare, which took place at relatively close ranges. Mortars continue
to be in used by militaries to the present day.
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 cover with plunging fire. Mortars are able
to fire from the protection of a trench or other type of cover. 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- and 300-mm calibre. 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 to operate
and less expensive than comparable howitzers or field guns.
A mortar can be carried by one or more people, 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. Heavy mortars 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 armoured personnel carriers, tank chassis, and coastal patrol boats. 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 .
Design
Most modern mortar systems consist of three main components: a barrel, a base plate, and
a bipod. Modern mortars normally range in calibre from 60 mm to 120 mm. 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
240 mm self-propelled mortar. Smaller mortars are commonly used and transported
by infantry based mortar sections as a substitute for, or in addition to, artillery.
Ammunition for mortars generally comes in two main varieties: fin-stabilized and spin-stabilized.
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, smoke, or high explosive.
Spin-stabilized rounds may be fired from a smoothbore or a rifled barrel. Since mortars
are generally muzzle loaded, mortar bombs for rifled barrels have a pre-engraved band,
called an obturator, that engages with the rifling of the barrel. They are more accurate,
but slower to load. Exceptions to this were the U.S. M2 4.2 inch mortar and M30 mortar,
whose ammunition had a sub-caliber expandable ring that enlarges when fired. This allows
the projectile to slide down the barrel freely, but grip the rifling when fired. The system
is reminiscent of the Minié ball for muzzle-loading rifles.
Mortars are made in a range of calibres. The French 81 mm mortar became standard for many
countries, while the Soviet bloc standardized on the 82mm mortar.
Mortars suffer from instability when used on snow and soft ground, because the recoil
pushes them into the ground or snow unevenly. A solution to this problem is the Raschen
Bag. Distinctive features of mortars
Modern mortars and their ammunition are generally much smaller and lighter than other artillery,
such as guns and howitzers, which allows light and medium mortars to be considered light
weapons; i.e. capable of transport by personnel without vehicle assistance. They are short-range
weapons, and often more effective than other artillery for many purposes within their shorter
range. In particular, due its high, parabolic trajectory with a near vertical descent, the
mortar can land bombs on nearby targets, including those behind obstacles or in fortifications,
such as light vehicles behind hills or structures, or infantry in trenches or spider holes. This
also makes it possible to launch attacks from positions lower than the target of the attack.
higher; a target easily accessible to a mortar.) 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 FO and its target, allowing for
fire to be quickly and accurately delivered to lethal effect.
Fin-stabilised mortar bombs do not have to withstand the rotational forces placed upon
them by rifling or greater pressures, and can therefore carry a higher payload in a
thinner skin than rifled artillery ammunition. 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. For example, a 120 mm mortar bomb has about the same explosive capability
as a 155 mm artillery shell. Also, fin-stabilised munitions fired from a smooth-bore, which
do not rely upon the spin imparted by a rifled-bore for greater accuracy, do not have the drawback
of veering in the direction of the spin. Spigot mortar
Spigot mortars, a particular type of mortar, consist of a mostly 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 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.
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.
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.
Images
See also List of heavy mortars
List of infantry mortars Carcass, used in mortars before the modern
age Military technology and equipment
Chemical mortar battalions of the United States Army
Strix mortar round Hedgehog World War II anti-submarine weapons
Barrack buster M2 4.2 Inch Mortar
2S4 Tyulpan Mortar carrier
Livens Projector References
Notes
External links "Field Manual 3-22.90 - Mortars". Department
of the Army. December 2007. Retrieved 7 January 2013.
"Field Manual 3-22.91 - Mortar Fire Direction Procedures". Department of the Army. 17 July
2008. Retrieved 7 January 2013. "Field Manual 23-91 - Mortar Gunnery". Department
of the Army. 1 March 2000. Retrieved 7 January 2013.
Mallet's Mortar, the largest British mortar ever made.
Defense Update: Modern Mobile 120mm Mortars Defense Update: Advanced Mortar Munitions
Mortars during World War I The Karl Morser, WW II-era German 60 cm self-propelled
mortar. Video