Mortars are smooth-bored indirect-fire infantry support weapons that enable users to engage targets that are outside their line-of-sight. Often referred to as the poor man’s artillery, mortars are as ubiquitous in the arsenals of modern militaries as they are amongst armed groups and guerrilla forces. The main differences between the two is the calibre used.
The defining features of a mortar are its responsiveness, high-angle arching trajectory (above 45°), low velocity and relatively short range. In the theatre of combat, mortars are used to kill military personnel, harass adversaries and prevent the use of ground with interdiction fire. They can also be used to lay smoke screens. (Photo credit: Israel Defence Forces)
What is the history of the mortar?
Early development
Mortars were first developed in the 15th century and are likely to have been used during the siege of Constantinople in 1453. In the mid-19th century, the small portable Coehorn mortar was used along with larger mortars during the American Civil War.
First use
The trench warfare of WWI necessitated high-angle infantry gun support. The modern mortar was born with the development of the Stokes mortar by British engineer Wilfred Stokes. The 76.2 mm muzzle-loading Stokes mortar could fire as many as 25 bombs per minute and had a maximum range of 732m. The much recognised system of sliding the bomb down the tube, with the force of the impact with the bottom of the tube then Initiating the propellant charge, is Stoke’s design.
Mortars usually are made up of three components: barrel (‘tube’; including a sighting mechanism), baseplate and the bipod. A mortar ammunition component consists of a fuze, a cartridge, propellant charges and the fin assembly. A complete round of mortar ammunition contains all of the components needed to get the round out of the tube and to burst at the desired place and time. Modern mortars can be dismounted and launched from the ground or mounted onto a vehicle.
Recent modifications
The most revolutionary development in mortar systems has been the introduction of precision guidance systems. Guided mortar systems claim to allow for precise targeting and increased first-round hit probability. The claim from many militaries is that they greatly reduce the potential for collateral damage and reduce the logistical burden. The reality, however, is that a mortar used in a populated area can produce devastating effects – both in terms of civilian harm and in terms of infrastructural damage.
Figure 1: The M252 81 mm mortar, currently in use by Canada, UK and USA (source: GlobalSecurity.org).
What are the different types of mortars?
The most commonly used calibre of mortars are the 60-mm, 81-mm, 82-mm and the 120-mm.
According to the Geneva International Centre for Humanitarian Demining (GICHD), NATO member states, as well as countries supplied by western manufacturers, tend to use the 81 mm calibre medium mortar. Former Warsaw Pact members, and countries supplied by former Warsaw Pact states and China, tend to use the 82-mm calibre medium mortar. The 81-mm mortar projectiles are often longer and more aerodynamically efficient than the 82-mm versions, and commonly have a further range. The 120-mm calibre mortars are the most common heavy mortars in service globally. It is designed to be towed and is usually mounted on a vehicle, but it can be used as ground-mounted.
Mortars of calibre of less than 100 millimetres are considered ‘light weapons’ by the UN. Mortars capable of engaging surface targets by delivering primarily indirect fire, with a calibre of 100 mm and above are defined as ‘large-calibre artillery systems’.
Mortars have a higher rate of fire than artillery guns, but this is usually reduced as calibres increase in size because loading becomes more cumbersome. The maximum rate for a medium mortar is some 30 rounds per minute; 15 rounds per minute for sustained fire. For heavy mortars, such as those in 120 mm, the maximum rate is approximately 16 rounds per minute, and just 4 rounds for sustained fire.
Figure 1: “Indirect Fire: A technical analysis of the employment, accuracy, and effects of indirect-fire artillery weapons”, ARES
While the exclusive focus of this explainer is on manufactured mortars, improvised mortars were used by the IRA during the Northern Ireland Troubles and first developed by that group as far back as 1920/1921. Their warheads were generally homemade explosive (ammonium nitrate and a fuel) or high explosive Semtex detonated on impact.
What are the dimensions and weight of a mortar (i.e. from largest to smallest)?
The lightest models weigh less than 7 kg and the heaviest models weigh approximately 144 kg. While some light mortars can be carried and operated by a single person, most mortars are crew-served weapons, typically used by at least two operatives. Heavier mortars, such as the 120-mm calibre, are fired by three to five operatives and will require additional team members or light vehicles to transport the munitions. Mortar dimensions are assessed in terms of calibre (the internal diameter of the gun barrel) and range from 60-mm to 240-mm.
What quantity of explosive can a mortar deliver?
Mortar rounds come in a range of sizes that reflect the degree of explosive power they release when detonated. According to GICHD, the most commonly used mortars contain anywhere between 400g and 144kg
What is the range of mortar?
Mortars can engage targets at less than 70 meters to 9,000m from the firer’s position. Medium mortars (61-99 mm) can fire at ranges of 100 m to 5500 m, while heavy mortars (100-120 mm+) have a range of some 500 m to 9,000m. The range of any given mortar systems depends on the cartridge which possesses the maximum range.
The range of any given mortar’s projectiles can be adjusted by the user. This can be done by altering the angle of the mortar barrel, with a higher angle reducing the range and a lower angle increasing it. The user can also increase the propellant load which will in turn increase the mortar’s range.
The high-angle trajectory means that mortars are effective against targets positioned behind elevated ground or tall buildings, dense jungles or narrow streets, thus enabling ground forces to engage adversaries dynamically and at relatively close range, while minimizing their exposure to direct enemy fire.
How accurate is a mortar?
There is little consensus on the (in)accuracy of mortar systems. Despite technological advances, the majority of artillery and mortars are still categorised as area weapons and their inherent inaccuracies remain.
Modern, guided, mortars can be relatively accurate. The 81-mm and 120mm Roll Controlled Guided Mortar (RCGM) have a circular error probable (CEP- the radius of a circle within which half of all the weapons fired are expected to fall or explode) of less than 10 metres. But these are not the mortars of the majority of weapons arsenals. And accuracy means very little in terms of preventing civilian harm if such a weapon is used a populated area. Furthermore, in 2015 the Small Arms Survey observed that no non-state armed groups had access to guided mortar systems, and they were in “limited service” in a number of states.
To put this into starker context: the standard 120-mm mortar only lands within 100m of the target 50% of the time and there was a 38% likelihood of a firing landing between 160m and 480m away from the target.
Mortar accuracy depends on how the systems are used, by whom, their maintenance, and weather conditions. Calculations on the accuracy of a mortar assume that the mortar is correctly aligned. In the theatre of combat – where mortars are frequently deployed by poorly trained, non-state actors – there is no such guarantee.
Increased accuracy also comes at a cost: while mortar systems can be adjusted to increase their accuracy “this is often not done in order to preserve some of the essential characteristics of the system: simplicity and speed”.
Thus, weapon specifications and real-world deployment are two different things. In AOAV’s interview with a former weapons investigator he explained that “generally, if there was a particular house you wanted to target, you would maybe fire five or six mortars and expect one of them to hit”.
Conventional mortars (with the exception of guided mortar systems) typically require two or more rounds to be fired in order to stabilize the firing platform and make corrections for weather effects etc. They are commonly ‘walked up’ to the target; each time a round is fired and misses, a forward observer is nearby to report where the rounds have landed so that the mortar crew can make necessary adjustments. Thus, while the first shot of a mortar, especially at maximum range, could be characterised as highly inaccurate, sustained fire accuracy may improve over multiple shots or salvos. Such ‘improvement’ however, in a city or town, can be devastating.
Claims of more accurate firing systems have been made by Alliant Techsystems (ATK) (now part of Northrop Grumman), such as the APMI 120mm mortar which employs GPS targeting. It boasts a CEP of 10m, though 4m is the average. The shells used for the AMPI, though, are $10,000 each.
The question of the accuracy or inaccuracy of mortars has had serious legal implications as to whether civilians and civilian infrastructure is directly targeted or the unintended victims of an indiscriminate attack.
How precise is a mortar?
As noted, the precision of indirect-fire weapons is generally expressed using CEP. So, if a mortar system had a CEP of 100m, this would mean that, if eight mortar rounds were launched at a target in the middle of a circle measuring 100m, only four would land inside. In this hypothetical example, the other four outliers could land immediately outside that distance or far away.
Despite technological advances that have improved the precision of the most expensive and capable models, most conventional, unguided mortar systems have relatively high CEPs for such a short firing range. Conventional NATO High Explosive 120-mm mortar bombs have a CEP of 136m at their maximum ranges, if an advanced fire control system is not used.
High precision is not always the intended effect of a mortar. Optimal precision (see below) results in a natural dispersion so that not all munitions strike the centre of the desired target
Who are the biggest manufacturers of mortars?
Mortars are extremely widely used and produced. According to the Small Arms Survey, nearly 50 countries have manufactured one or more types of mortars – with 30 continuing to do so as of 2008 – making it the most widely produced light weapon. A 120-mm towed smoothbore mortar costs around $370,000 per system.
Where are mortars used?
Data from AOAV’s Explosive Violence Monitor reveals that the five countries with the most mortar attacks – Syria, Iraq, Pakistan, Afghanistan and India – accounted for around 72% of all mortar attacks worldwide.
Who typically uses mortars?
According to the Geneva International Centre for Humanitarian Demining (GICHD), ‘Mortars are found in the inventories of almost all state armed forces, and a majority of larger non-state armed groups’. Mortars are inexpensive to manufacture and simple to operate, rugged, portable, light, inexpensive and versatile. Given the low cost, availability and ease of operation of mortars, they have found favour among non-state armed groups.
AOAV data indicates that 40% of all incidents of mortar harm in the last decade have been perpetrated by non-state actors. State actors account for 20% of mortar attacks and the perpetrator status is unknown for 38% of incidents.
Different actors employ different mortar calibres. Mortars of a 60-mm calibre and less are largely regarded as obsolete by state armed forces. Medium mortars of 81-mm or 82-mm calibre, are in service with most armed forces and many non-state armed groups. Heavy mortars, such as the 120-mm system, are also used by many major state armies (though not by the British military who use the L118 105 mm Light Gun).
What types of injury do mortars cause?
According to AOAV EVM data, between 2011-2020, 13,385 civilians were killed and injured by mortars, at least 514 were women and 1,418 were children. During the same period 1,598 armed actors were casualties of mortars. For every mortar attack an average of 8.5 civilians are killed or injured.
Mortars have the capacity to induce the four mechanisms of blast injury. As is the case with other high explosive munitions, the majority of injuries are caused by fragments that are released on impact, or from secondary fragmentation produced when debris breaks off nearby structures (secondary and tertiary blast injury).
We know that buildings reflect and magnify blast waves – at times up to 8 or 9 times – rather than allowing them to dissipate. As such, whilst permanent structures are likely to provide protection from fragmentation, they increase the risk of suffering serious, or fatal, blast injuries.
If someone is close enough to a high explosive round from a larger mortar (120mm or bigger) and they aren’t already shredded from the fragmentation, the pressure from the blast may also cause damage; especially if the bomb detonates in a confined space.
Weapons manufacturers are developing “preformed fragmentation” in mortar bombs, with the potential to increase a mortar’s area effects and offensive capability. Saab produces a mortar round called THOR, a 120-mm calibre bomb which contains 4,250 steel balls in the casing to produce high lethality upon detonation.
Mortar rounds have a very high lethality. In 1994, a single round from a 120-mm mortar killed 68 people and injured 144 when it was fired onto a marketplace in Sarajevo. Mortar injuries are primarily caused by the velocity of fragmentation and this is exacerbated when detonated in densely built up areas which reflect the blast, as was the case in the 1994 Sarajevo explosion.
What patterns of harm do mortars cause to surrounding environments and infrastructure?
AOAV data shows that in the last decade 76% of mortar attacks took place in populated areas, 30% of these in urban residential locations. Indeed, military analysts regard mortars as “an essential weapon system” in Military Operations in Urban Terrain (MOUT). However, the inaccuracy of mortar fire means that when mortars are deployed in populated areas the effects cannot be reliably contained within the target area. Housing, schools, hospitals, markets, and places of worship are all too often caught in the firing line.
Modern, high-explosive, mortar rounds are listed as both anti-personnel and anti-material weapons. The 120-mm mortar is powerful enough to penetrate buildings and destroy field fortifications. Rudimentary structures will often be completely destroyed by the initial blast wave, and provide little protection from fragments – allowing them to travel far greater distances.
The angle at which a munition impacts the target has a significant bearing on the size and shape of the lethal area. Put simply, the higher the angle (toward vertical 90°) of fall, the larger the lethal area will be. The shelling of Sarajevo’s Markale market in 1994 shows the destination caused by firing a single munition at a high angle.
The large amount of heat given off at the initial point of detonation may also cause fires in areas with an abundance of flammable material. Unexploded mortar shells can block roads and restrict access to areas in need.
Mortar shelling of industrial facilities in eastern Ukraine has caused significant environmental damage, with chemical spills contaminating large surrounding areas. In May 2015, the OSCE reported that a coke-chemical plant in Avdiivka was hit by 45 artillery and mortar rounds creating fires and an ammonium leak. Mortar rounds typically contain elements such as lead, antimony, dinitrotoluene, trinitrotoluene, and hexahydro1,-3,5-trinitro-1,3,5-triazine (RDX) which are ‘generally resistant to biological treatment and remain in the biosphere’ – the contamination often has toxic environmental effects and can result in harm to human health.
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