Over The Top

This article is published in our April/May 2016 Issue.

Elbit Soltam smoothbore 120mm mortar
The US Army adopted the Elbit Soltam smoothbore 120mm mortar which is designated M120 in the ground bipod version. It is employed at battalion level. (US Army)

Mortars are a class of artillery. They differ from guns which have a low, flat trajectory best suited for engaging targets by direct fire and howitzers which typically engage targets not seen from the gun position with an arching trajectory.

The mortar fires a projectile at a high angle allowing it to hit targets behind hills, in narrow streets, and inside ravines and trenches; the latter capability made it especially useful in First World War trench warfare. It can be a very simple system: just drop the round down the tube and fire as quickly as the soldier can drop rounds down the tube (20 rounds per minute; one every three seconds is easily possible). Plus, this system is portable, a light mortar can weigh under 23 kilograms/kgs (50 pounds/lbs) and even a heavy towed mortar is but 150kgs (330 lbs) ready to fire which compare favourably to even the BAE Systems M777 155mm lightweight howitzer at 4200kgs (9300lbs). Yet it can reach out to 3.5 kilometres/km (2.1 miles) for light mortars up to ten kilometres (6.2 miles) for the latest heavy weapons.

The mortar started out primarily as a siege weapon that could fire over the walls of fortifications to destroy the guns and structures behind them. Since their re-introduction in the First World War, the British Stokes Mortar saw widespread use during the Second World War, where it took on an important, though often overlooked role in many theatres. In fact, Wehrmacht (Nazi Germany’s combined armed forces) doctrine saw mortars as the primary indirect fire support for the infantry as ‘tube’ artillery would be reserved for the schwerpunkt or ‘main attack’. Here it established itself as the small unit ‘hip packet’ artillery; a role which it generally continues to play today.

Modern mortars fall into three categories: light mortars (generally 60mm calibre) used at platoon and company level, medium mortars (81mm in western or 82mm in Russian/Chinese weapons) used at company or battalion level, and 120mm mortars at battalion and used in direct fire support units. Regarding dismounted infantry, the tendency is to have the 81mm at battalion level whereas mechanized units usually have the 120mm mortar mounted on a vehicle. Today’s mortars are lighter, have longer range, greater accuracy and more lethality than those fielded just fifteen years ago. This is the result of the introduction of new metal and composites in the mortar tubes and base plates, automation and digitization of fire control, and advances in fuses and ammunition. These improvements have enhanced the mortar’s capabilities to fill its direct support roles despite changing dynamics of ground combat with extended frontage, more diverse operations and asymmetrical warfare. In fact, a strong case can be made that these conditions increase the importance and contribution of the mortar to tactical commander.

Light Mortars

Which weapon is most suited for employment as organic to a particular unit level is influenced by two primary factors; first how does it fit within the mission responsibilities of that unit level. In particular, does it match the area of interest and of action responsible to it? Second, is it compatible with the units’ ability to deploy the system; i.e. can they move it and support it? Though there are advantages to have a weapon with longer range, if it requires too many soldiers to carry or additional equipment, it might not be practical. The difficulties of moving the piece and providing sufficient ammunition can negate the value of the additional range. A balance needs to be struck. A general consensus among armies is that the 60mm mortar is the best choice for light infantry company. The US Army FM7-90 Tactical Employment of Mortars manual stresses: “The value of the 60mm mortar … is its immediate responsiveness to the company commander’s orders and the speed at which it can be brought into action.”

The US Army and Marine Corps employ the M224 LWCMS (Lightweight Company Mortar System) with an effective engagement range of from 70m (229ft) to 3489m (12627ft). The minimum range is as important as the maximum as it indicates how close in front of friendly troops the weapon is capable of placing fires. This can be critical in overcoming an assault that is threatening to overrun a position or blasting out an enemy determined to hug friendly positions so as to avoid opposing artillery fires. The M224 and even the 20-percent lighter M224A1 are supplied by General Dynamics Ordnance and Tactical Systems (GDOTS). This weapons family fires High Explosive (HE), Smoke (both white and red phosphorus), Illumination (visible and infrared) and Practice projectiles. Saab meanwhile offers a Multi-Purpose Anti-Personnel Anti-Material round (M1061 MAPAM) which can be used with the M224/A1 and is able to be used more closely to blue forces due to its more controlled fragmentation pattern and the ability to penetrate a roof or even light armour and detonate inside.

The M224 LWCMS is a 60mm system that is carried by its four person crew. It is organic to US Army light infantry and Marine Corps companies providing responsive high explosive, illumination and smoke in support of small unit manoeuvre and defence. (US DoD)

Away from the US, the Hirtenberger M6 Mortar is a 60mm lightweight infantry weapon. In addition to the Österreichisches Bundesheer (Austrian Army) it was adopted by the British Army and Royal Marines as the M6-895 with a maximum rage of 3800m (12467ft). The British fielding reversed an earlier plan that would have eliminated the light mortar in favour of the handheld grenade launcher. However, combat experience during the UK’s intervention in Afghanistan between 2001 and 2013 highlighted the benefits of the light mortar causing the substitution to be rethought. The tripod mounted Automatic Grenade Launcher (AGL) is also sometimes seen as a substitute for the light mortar. However, the flight characteristics of the AGL are closer to the arching fires of a howitzer. This makes it difficult to reach reverse slopes with the AGL. Moreover, they do not have the diversity of other mission rounds such as illumination and smoke.

An aspect of the 60mm mortar is that, though most accurate and long range fires are performed using the bipod and T and E (Traversing and Elevation) mechanism, it can also be handheld and visually aimed for quick engagements. Leveraging this technique, DSG Technology/Mortars has introduced the iMortar, an ultra-lightweight 60mm mortar designed for small unit use. At 5.5kgs (twelve pounds) and 900mm (36 inches/in) in length with integrated aiming, it is well suited to the small team which is also reflected in its short 1.2km (0.7 mile) range.

Medium Mortars

The 81mm calibre (actually 81.4mm) is most common in western armies while the 82mm is found in Russian and Chinese weapons. Although common in Russian units during the Second World War, the 82mm has been replaced by the 120mm in most of Russian Army units. The exception was the use of the 2B9 Vasilek, an automatic 82mm gun-mortar on a wheeled carriage fielded in 1970 and used during the Soviet Union’s intervention in Afghanistan between 1979 and 1989. It is still in use by Russian airborne forces. Unlike conventional mortars, it fires in either a single or automatic mode using four-round clips to a range of 4270m (14009ft) with high explosive, smoke, illumination and anti-armour rounds. The Chinese People’s Liberation Army uses the Type 67, a modernization of the Soviet PM-41 mortar first fielded in 1941. This mortar was widely used in the Vietnam War.

The US has applied technology to improve its 81mm mortars with the latest being the M252. At 42.3kg (93 lbs) it is found at the battalion level in army light infantry and is used by the Marine Corps. The 81mm mortar was also used in the M125 a BAE Systems M113 Armoured Personnel Carrier modified to carry and fire the mortar through a roof hatch. It is also used in the Marine Corps’ General Dynamics Land Systems’ (GDLS) LAV-M Mortar and carried for dismounted support with the GDLS M1129 Stryker mortar carrier. The M252 has a range of 5608m (18398ft) firing the full range of 81mm ammunition.

US Army Stryker units
High mobility is one of the key tactical advantages of the US Army Stryker units. Having an immediately responsive indirect fire capability is critical to maintaining that manoeuvre advantage. (US Army)

The Mo-81mm LLR (Léger Long Renforcé/Reinforced, Light, Long) from Thales TDA Armaments is used by the French and Irish Armies and is offered with a 1.1m (3.7ft) short barrel (Léger Cour) and (Léger long) and with a 1.5m (4.9ft) barrel. It has a standard range of 3100m (10170ft) but special extended range ammunition extends this to 5600m (18372.7ft). Elsewhere in France, Nexter is in the business of supplying mortar ammunition via its Mecar subsidiary which produces a range of mortar ammunition, such as the 155mm MPM (Metric Precision Munition) which has a maximum range of 40km (24 miles), while the company has also developed a version of its VBCI (Véhicule Blindé de Combat d’Infanterie/Armoured Infantry Combat Vehicle) in use by the French Army as a 120mm mortar carrier, although no sales of this version of the vehicle have yet been performed.

All 81mm mortar rounds are fin-stabilized with the most prevalent being the high explosive round. The introductions of multi-option fuses for high explosive allow the gun crew to easily select the detonation of the projectile just prior to firing. Such fuses like the M734 can be set to detonate on impact, delayed (allowing it to penetrate a roof or bunker) or proximity (exploding above the ground which spreads the explosive shrapnel in a wide area from above the target). Illumination projectiles carry an illuminant ‘candle’ that burns at 525,000 candle power suspended from a parachute. The time fuse is set by the crew so that the case separates over the target igniting the illuminate which then burns for 50-60 seconds. The illuminate composition can be configured to provide either visible or infrared light. Smoke projectiles are filled with a composition of red phosphorus pellets that are ignited to burn providing a dense obscuring smoke. White phosphorus is another mortar projectile that produces smoke and does so instantaneously while defeating both visual and thermal imaging. It burns fiercely and can cause burn casualties, but due to its instantaneous effect it is ideal for marking targets.

Heavy Mortars

The 120mm mortar has for over the last 20 years begun to prevail as the calibre of choice in heavy mortars. In some units the heavy mortar is used as an artillery weapon. This is the case with the US Marines’ Expeditionary Fire Support System (EFSS) from GDOTS which equips battalions in the Marine Artillery with this 120mm rifled mortar, derived from TDA Armament’s Mo 120 RT. The EFSS is used to support the vertical assault element as it is designed specifically to be carried inside Sikorsky CH-53E Super Stallion heavylift helicopters and Bell-Boeing CV/MV-22B Osprey tilt-rotors. The EFSS M327 mortar is towed by a specially-designed lightweight prime mover and can be set up in four minutes and fire up to four rounds-per-minute out to eight kilometres (4.9 miles).

Elbit Soltam smoothbore 120mm mortar
The US Army adopted the Elbit Soltam smoothbore 120mm mortar which is designated M120 in the ground bipod version. It is employed at battalion level. (US Army)

The US Army has also moved to the 120mm mortar via its smoothbore M120 Mortar derived from the Elbit Systems’ Soltam K-6. It has a range of 7200m (23622m) but like all heavy mortars the 150kg (330 lb) firing weight dictates that it either be towed or mounted on a vehicle. The US Army mounts the M121 (vehicle version) on its M1064 (M113-based) mortar carrier and on the M1129 Stryker. The Soltam Cardom used on the M1129 takes target acquisition data and translates it to traverse and elevation angles which are automatically sent to the gun to prepare for firing. The Cardom can come into action in under 30 seconds and has a burst rate of 16 rounds-per-minute (rpm) and a four rpm sustained rate of fire.

120mm heavy mortars
Towed 120mm heavy mortars have been adopted by the US Marines to provide a helicopter transportable indirect fire capability to the vertical assault element. The EFSS uses a TDA 120mm rifled mortar with a Growler light prime mover. (USMC)

Providing mobility to the 120mm mortar has been a focus of many efforts over the years and continues today. The approach taken is determined by the end user force; is it a light or armoured force? For light forces one solution is offered by Boeing—a version of its Phantom Badge. This lightweight combat support vehicle has been configured with a 120mm mortar mounted in the back. An accompanying trailer carries ready ammunition. Elbit Systems SPEAR uses a special soft recoil system allowing the mortar to be mounted in the bed of a light vehicle like the AM General HMMWV (High Mobility Multipurpose Wheeled Vehicle) or even a modified pick-up truck. They have already secured a contract to provide SPEAR to the Royal Thai Army. Steve Rust of Mistral indicated to Armada that “US Special Forces using Elbit soft recoil mortars in Afghanistan found they offered a ideal solution for providing immediately responsive fires not previously possible for light truck mounted forces.”

Elbit’s SPEAR
Elbit’s SPEAR reduces the recoil forces of mortar firing sufficiently to allow the weapon to be mounted and accurately fired from a light tactical vehicle. The system has already been employed by US Special Forces on pick-up trucks in Afghanistan. (Elbit)

For armoured forces the development and fielding of turreted 120mm mortars and gun/mortars is gaining attention. Rather than firing through a roof hatch from a platform with the round dropped down the tube, these mortars are mounted in a mantel and loaded from the breach. Some recent systems are automatically loaded and can engage with both indirect and direct fires. The Patria/BAE Systems AMOS (Advanced Mortar System) is used by the Maavoimat (Finnish Army). Its dual 120mm mortars in a 360-degree traversing turret can fire 16 rounds-per-minute. By integrating Global Positioning System (GPS) geolocation and inertial navigation and the fire control system the AMOS can move into a position, fire a 14-round salvo and then displace in under 30 seconds. It also allows Multiple Rounds Simultaneous Impact (MRSI) where one AMOS can fire up to 16 rounds so that all hit the target at the same time. The system automatically adjusts the firing angle of each round so that they all hit simultaneously. Patria’s NEMO is essentially a single barrel version based on AMOS. Jukka Tiainen, Patria’s technical manager weapon systems suggested, “the major advantages of the Nemo unmanned turreted mortars are that they have the same mobility as units they are supporting while providing continuous protection to the crew. Plus, the combination of auto-loading and automated firing allows one NEMO to deliver fires equivalent to a full battery of traditional guns.”

AMOS is a turret-mounted 120mm mortar
The AMOS is a turret-mounted 120mm mortar with twin tubes that is automatically loaded and trained. As a result a single AMOS can deliver the equivalent rounds on target as a full battery of conventional mortars. (Patria)

The Polish Armament Group unveiling in late 2014 of its RAK-120 turreted mortar on the Rosomak (the Polish-built eight-wheel drive Patria Armoured Modular Vehicle) suggests that other armies have recognized the benefits and broader tactical applications of the turreted approach. One of these is their direct fire capability which permits their use in an assault support role. Turreted mortars can engage bunkers, buildings and fortifications to 1500m (4921ft) with high accuracy. The Russian semi-automatic loading rifled 2S9 Nona-S 120mm howitzer/mortar system (on the Volgograd Tractor Plant BMD amphibious airborne infantry fighting vehicle) and 2S23 120mm SP howitzer/mortar (on an eight-wheel drive Arzamas BTR-80 chassis) fill a similar role. The Russian Motovilikha Plants Corporation latest fielding in the Nona family is the 2S31 Vena, an automated self propelled mortar with a longer barrel mounted on the Kurganmashzavod BMP-3 amphibious infantry fighting vehicle. In addition to conventional rounds it also fires the Gran laser-guided bomb against point targets at a range of 13km (eight miles). Mortar carrier variants of the BTR-3 eight-wheel drive armoured personnel carrier are available from Ukraine’s Ukrspecexport state armaments export company which has supplied the BTR-3M2 mortar carrier to the Royal Thai Army as of 2013.

Precision Projectiles

One benefit of the 120mm mortar round is its greater explosive power. The 81mm projectile carries around four kilograms (nine pounds) of explosive while the 120mm carries 13kgs (29 lbs). Another benefit is that it is more easily adapted to advanced ammunition types including ‘cargo’ sub-munitions and precision guided projectiles. This is not to suggest that 81mm guided projectiles are not possible; in fact BAE Systems and GDOTS have both demonstrated the 81mm RCGM (Roll Controlled Guided Mortar). It modifies the existing British mortar bomb with GPS guidance, canard controls, and an M734A1 multi-option fuse. So adapted, the round can impact within five metres (16ft) of its designated target. It can be fired from the existing L16 or M253 mortars. It provides target coverage with two rounds that with conventional engagement techniques would require ten.

It is this increased fire efficiency that drives the interest in PGMs (Precision Guided Munitions). Considering that, for example, the M1129 Stryker Mortar carrier carries 60 rounds (which also include smoke and illumination), using PGMs allows ten-fold increase in engagements from on-board stowage. The US Marine Corps Precision Extended Range Mortar program or PERM is being led by Raytheon in collaboration with Israel Military Industries. It uses a GPS-guided 120mm projectile which in 2014 test firings achieved ten-metre (32.8ft) accuracy. An added benefit is that the canards used to steer the projectile allow an extended range of up to 16km. Orbital ATK has developed a similar GPS guided projectile kit known as the XM395. It is based on its 155mm artillery guided projectile. Both the PERM and XM395 can be used by rifled or smoothbore mortars.

Precision Extended Range Mortar PERM
Raytheon was awarded a contract to deliver its Precision Extended Range Mortar PERM for the US Marines’ 120mm mortars. It provides an increased range of up to 16km as well as first round accuracy with a circular error probable better than ten metres. (Raytheon)

Saab’s Bofors Dynamics division has taken another PGM path seeking a direct hit with its STRIX 120mm terminally-guided mortar projectile. The head has an infrared imaging sensor that detects and locks on to the heat signature of a target and then guides itself onto it. It is considered an anti-armoured vehicle round in that by attacking the thinner roof of the targeted vehicle it is likely to penetrate and disable or destroy it. The system offers a unique organic capability to engage armoured forces assembling to attack even when hidden by terrain. STRIX has been in service with the Swedish and Swiss armies’ since the late 1990s. The GRAN is another 120mm thermal guided mortar round from KBP in Russia but its seeker homes in on the radiated signal from a laser designator usually operated by a ground observer. It has a range of 1500m (4921ft) to nine kilometres.

Evolving Capabilities

The combination of highly accurate position determination of both targets and firing mortars with digital computing of firing solutions has made them even more responsive and accurate. Where previously adjusting firing on to a target might require three shots before ‘firing for effect’, this adjustment process can be reduced to one round or even eliminated entirely. The closed loop system that links the forward observer to the gun and automatically computes and applies the firing solution further refines this process. Adding automatic loading permits single and dispersed weapons to match the target effect that previously required six or more guns firing in battery. The addition of precision guided projectiles and the turreted mortar allow the mortar to undertake point target and direct fire support missions for the small unit. Together these advances are altering the way that mortars are being used and expanding roles that they are playing in combat. The technical and performance improvements have been demonstrated; it is now up to the soldiers to evolve their tactics and employment to capitalize on what these can offer.

by Stephen W. Miller