Technology Insertion to Develop Mortar Systems for the Modern Battlefield

Introduction

Mortar weapon systems have traditionally provided the indirect fire support for infantry units. The use of heavy mortars within light armoured and reconnaissance units is likely to increase as armies are re-structured to meet the needs of the changed world order, with an emphasis on strategic mobility without loss in the deliverable fire power available to units designed for general warfare. The cancellation of the Crusader programme in the USA in May 2002 clearly demonstrated that most 155-mm artillery systems either in current use or development are probably too heavy or too cumbersome to support rapid force projection operations. Organised armies are not the only users of mortar weapons. Their continued utility, even in the hands of relatively unskilled users without the command and control systems available to western armies, was graphically demonstrated in Afghanistan in March 2002 when elements of the US 10th Mountain and 101st Airborne Divisions were pinned down for hours by mortar fire on their helicopter landing zone.

The re-structured armed forces must be able to apply the necessary level of force in the correct timeframe to be able to influence the outcome. To be credible, these forces require integral fire support, both direct and indirect. Most current artillery systems are either self-propelled (and therefore too heavy to be strategically mobile), or towed (and therefore require multiple vehicles to deploy a single firing platform). A highly mobile and lethal indirect-fire system is essential to provide the force commander with dedicated offensive support to the early entry forces, but yet which has the capability to provide continued support for the sustainment and heavy forces. To provide this utility, however, there needs to be a better understanding and dialogue between both suppliers (what might be achievable in the way of weapon systems development) and the user (what tasks the mortar might be required to complete). In these discussions, the operational, logistical, and legal (human factors and safety) issues also need to be addressed.

Most in-service smoothbore mortar weapon systems are based on designs that are more than 40 years old. Since then, there has been only limited insertion of technology building blocks that have delivered a very slow evolution of the current systems, rather than faster revolutionary improvements. The requirements described above and the capability gaps that users are now attempting to close, in order to deliver the level of deployed firepower, have provided the impetus for industry to develop a number of enhancements to mortar systems. In addition to firepower improvements however, mortar weapon systems require improvements in mobility and protection / survivability to deliver the required capability.

Firepower improvements

There are a number of factors, or characteristics, that contribute to improving the firepower of mortar weapon systems, including:

• improved fragmentation for HE bomb body material;
• improved fuzing—use of lower cost and more effective air burst fuzes;
• improved consistency;
• improved accuracy;
• improved range through the use of increased muzzle velocity;
• introduction of new and improved natures of ammunition; and
• introduction of improved C4I systems into mortar units.

A number of the improvements outlined above either have been or are being developed in parallel with or subsequent to similar programmes in the artillery systems area. However the single most important factor in developing the firepower of mortar systems is in the area of electronics, which will provide information on weapon and target survey and also accurately transmit the ‘call-for- fire’ data.

Improved fragmentation

The material used in the manufacture of high explosive (HE) mortar bomb bodies remains the subject of some debate. In many cases the material characteristics have not been improved for over 50 years and these bombs produce only a limited target effect. A number of artillery shell types are equally ineffective, but for different reasons. The poor lethality of HE mortar bombs is most likely to be caused by one of the following:

• the use of brittle material, such as untreated cast iron, which is likely to over-fragment and create non-lethal dust; or
• the bomb body material over-matches the explosive payload (as in the US 155-mm M107 HE shell which is filled with TNT. In this case, the body may only produce a ‘few’ large fragments close to the impact point).

In recent years, artillery shell design has improved with shell-casing material specifically developed to produce high fragmentation characteristics. When these casings are combined with powerful RDX/TNT type payloads, the effectiveness of these shells has improved considerably.

Modern 81-mm mortar bombs, such as the RO Defence L41 HE bomb, are more effective. They have been designed to create maximum lethality through the material design of the casing. This bomb uses a spheroidal graphite cast-iron body with a RDX/TNT payload and tests have shown that more than 75% of the body material creates lethal fragments in the 0.08–5.0 gram range, and only minimal dust. This size of fragment is ideal for the attack of personnel and other soft targets. A number of other materials are equally efficient in producing effective fragmentation.

The amount of damage caused by any fragment is determined by the mass and velocity of that fragment, its ability to transfer energy by creating shock waves in human tissue, and its relevant stability after entry into the target. Where the fragment becomes unstable in the human body, which is more likely to happen with the casing of a fragmenting projectile than with a bullet, the level of damage increases dramatically due to any change of direction, as there is an increasing level of damage to the surrounding tissue. A similar level of damage will be caused to soft-skinned vehicles.

In comparison, fragments from the L41 81-mm mortar bombs described above are insufficiently large to cause major damage to buildings or armoured vehicles. However most modern 120-mm Mortar HE bombs are manufactured from forged steel to permit firing at higher muzzle velocities with corresponding higher g-forces and thus require higher material strength. As a result, these bombs now produce an increased number of larger fragments, which are more effective against hard targets and armoured vehicles, whilst still being effective against personnel and soft targets.

Fuzing

The provision of suitable fuzes for HE mortar bombs has always been difficult and in some cases expensive, in relation to the overall cost of the bomb. Many early fuzes had a poor safety record, which was caused by their premature function during flight. As a consequence, most armies banned the firing of mortar bombs over the heads of troops, except during operations.

Subsequently, dual safety systems were introduced making modern fuzes, such as the DM 111-A4 and the M935, much safer during handling and firing. Smoothbore mortar ammunition uses the fin unit at the rear of the bomb, rather than spin, to provide ballistic stability. Consequently, spin, which is one of the primary safety and arming modes used in most other types of fuze, is not available to the mortar fuze designer. For more than 50 years, mortar fuzes have relied upon a safety pin to hold the striker in a safe position, prior to loading into the barrel. Only once the safety pin has been removed and the round fired will setback allow the mechanical parts of the fuze to bring the striker into line with the detonator and the firing chain.

Proximity (Prox) and Multi-option (MOF) mortar fuzes have been in limited service for many years, but are still relatively expensive in comparison with impact fuzes. An HE bomb fitted with a MOF will produce an increase in lethality, mean area of effect, of about 25%, in comparison with a similar bomb fitted with an impact fuze. A MOF may well cost about the same, or even more than, a complete 81-mm bomb fitted with an impact fuze. Many users are not prepared to pay the premium for this limited increase in lethality. However, the relationship between the price of an MOF fuze to the overall price of a 120-mm HE bomb is considerably less, which means that in the future airburst fuzes will become more common in the mortar ammunition inventory

Induction fuzes

To provide improved safety and functionality, and to reduce crew handling, a number of programmes are currently under way to develop and type classify a new inductively set mortar fuze. The introduction of a single induction fuze with the capability to replace the current impact/delay, mechanical time and proximity/MOF fuzes will reduce the training load and increase the safety for both the mortar crew and those troops who have requested the fire support. Induction fuzes are already in service on medium-calibre cannon ammunition, such as the Rheinmetall Air Defence (Contraves) ‘AHEAD’ air defence system, which uses an induction mechanism to measure the velocity of the round before setting the fuze to function at the predicted impact point with the target.

Before the introduction of this type of mortar fuze, users will require fire-control system units / ballistic computers at the mortar weapon to provide the data required for the electronic setting of the fuze. This may be carried out by either ‘passing a wand over the fuze’ prior to the bomb being loaded, or an induction coil may be placed around the breech and the data passed prior to firing. This is an ideal method of operation for breech-loaded mortar weapons and for those muzzle-loaded weapons fitted with a mechanical firing device.

Consistency and accuracy

The consistency and accuracy of weapon systems are inextricably linked. Consistency relates to the size of the Gaussian distribution of impact points around a mean point of impact (MPI), whilst accuracy relates to the position of that MPI in relation to the specified target. Information on consistency will be available from test results or in the range tables for specific weapon and ammunition combinations. Accuracy for indirect weapon systems, such as mortars, will conversely normally only be measurable during specific firing trials or possibly during individual fire missions.

Historically, mortars have been both inconsistent—the standard deviation has been large—and inaccurate, because mortar platoons have traditionally used a map plot from triangulation, at best, for both mortar and target location and a prismatic compass for direction, with an average accuracy of ±20 mils. As a result, the possibility of first round on target was limited.

The introduction of certain technologies has over the recent past improved, and is still improving, both the consistency and accuracy of mortar weapon system.

Consistency—weapon and ammunition interfaces

To enable muzzle-loaded mortar bombs to fall freely onto the fixed firing pin; there must be an air gap between the maximum diameter of the bomb and the minimum diameter of the barrel. This gap is traditionally called ‘windage’.

Ammunition designers, however, need to achieve a gas-tight seal to regulate the pressures achieved in the barrel and subsequently the muzzle velocity with the consequential effect on the consistency. In a rifled weapon, such as a rifle or artillery howitzer, this gas seal is achieved by fitting an oversized copper driving band, which is located onto the rifling before firing and is then deformed as the projectile is forced up the barrel by the propellant gases.

Early mortar bomb designs used a canalure system of multiple grooves cut into the widest point of the bomb body. A level of sealing was created by the turbulence in the high-speed gases at this point. During the 1950’s, Royal Armaments Research and Development Establishment (RARDE) in the UK developed the expanding obturating band, which is located in a single groove at the widest point of the bomb and expands to fill the air gap whilst the bomb is being propelled up the barrel. The application of this design was first seen on the ammunition supplied for firing from the L16 81-mm mortar weapon and produced the most consistent weapon system of its day, when initially fielded in 1967.

In addition to the expanding obturating band, the weapon system designer is able to assist the ammunition designer by reducing the level of windage—in the case of the RO Defence L16/F2 81-mm weapon, this gap is no less than 0.6 mm. In the 120-mm Armoured Mortar System (120-mm AMS) windage has been further reduced. As part of the systems engineering process, the level of windage must be assessed in relation to any residue remaining in the breech area after firing. This may cause problems, primarily with muzzle-loaded weapons, where bombs need to fall freely with sufficient velocity onto the fixed firing pin to ensure that the charge is initiated.

As an alternative method of improving the consistency of mortar systems, Thompson Brandt Armaments (TBA) now Thompson Daimler Armaments (TDA) developed their 120-mm muzzle-loaded rifled mortar system (RT-61). This system uses a projectile with a ‘pre-engraved’ driving band and a tail section holding the charges, which is detached as the projectile exits the muzzle, thus allowing the spinning projectile to fly in a similar manner to an artillery shell. In comparison with ground-fired muzzle-loaded 120-mm mortar weapon systems, which were generally designed during the 1950s, this weapon has provided considerable improvements in consistency.

Most smoothbore mortar ammunition designers have now copied the expanding obturating band into their own designs, however there remains only one primary source of rifled mortar weapons and ammunition.

Consistency—weapon and mountings

In the ground-fired role, in order to provide a stable platform for the baseplate, mortar crews will normally try to prepare the firing position before setting up the weapon. Any major movement of the baseplate downward or backward will have an adverse affect on the original weapon/sight relationship with the aiming post and subsequently the consistency, especially if this movement takes place during a fire mission. The considerable firing forces, generated in the breech, are transmitted through the breech plug into the baseplate socket, which is normally a rotating device located centrally in the baseplate. The baseplate is then used to spread and transmit these forces into the ground.

The larger the diameter of the baseplate the more efficient is the dissipation of the forces. However for man-portable 81-mm mortar systems (the vast majority of the weapons in this calibre are potentially man-portable), the weight of this item must be kept as low as possible. The underside of most baseplate designs is manufactured to cut into the surface of the ground before compacting the soil to provide a stable platform. Some now have sectors cut out to remove the possibility of air being trapped below the plate, which may cause bounce during firing. A system trade-off will almost always be required including strength of design, weight and material.

In the highly mobile scenarios now being discussed, whether involving armoured and mechanised heavy forces or lighter forces, mortar crews will not have the time or the luxury to fully prepare their firing positions. Most fire missions are now expected to be immediate neutralization with the supported forces in contact, rather than the more deliberate missions of previous operational scenarios. The alternative solution is therefore to raise the weapon off the ground.

Vehicle mounts were developed during the 1960’s to integrate both 81-mm and 107-mm (4.2-in) mortars into tracked APCs. These provided both elevation and traverse control fitted to a rotating platform. The mount designs were initially driven by the requirements of the chassis designers and their ability to strengthen the lower parts of the hull. The UK mount involved minimal strengthening of the chassis by fitting the rotating platform to a heavy base mount. The firing forces are transmitted through the platform to the base, which becomes the recoiling mass. This was mounted into the FV432 chassis by 12 mounting bolts. Calculations and trials have indicated that the firing loads actually transmitted to the chassis are reduced by approximately 85% to a maximum of about 8 tons. In the USA, the mount developed for the M113 family of vehicles involves strengthening the chassis to accept the full recoil load, which in the case of the latest M1064A3 heavy mortar carrier is in the order of 110 tons force.

More recent vehicle mounts designed for muzzle loaded 120-mm mortar weapons, all firing standard ammunition to a range of 7–8 km, have integrated a recoil system. Although the recoil length is limited by the ability of a crewman to load a round into the muzzle, the firing loads are reduced to about 40% of the unrecoiled force.

Mortar users are now writing requirements for new weapon systems with ranges in excess of 10 km, which are based on the expected future operational need. The firing forces, developed by this new ammunition, will increase by at least 50% those for current 7–8 km muzzle-loaded 120-mm mortar systems. The recoil systems fitted to current muzzle base mounted systems, described above, are therefore unlikely to be able to protect the light-to-medium weight chassis that are being brought into service, such as the LAV 3 IAV for the US Army Brigade Combat Teams. As a result, a number of turret-mounted mortar systems are being brought into service where the recoiled forces transmitted through the trunnions (pivots) are reduced by up to 90%. This has enabled light weight mortar turret systems, such as the RO Defence / Delco Systems 120-mm AMS, when firing these new natures of high-pressure ammunition, to be safely integrated on lightweight tracked and wheeled chassis with a GVW from about 13.5 tons.

Consistency—weapon laying

Weapon laying for ground fired mortar weapons has always been notoriously inconsistent for a number of reasons—limitations of the optical sight, inability of the mortar gunner to maintain the bubbles in the centre of their glass runs and movement of the baseplate and the consequential change in relationship of the sight and aiming post.

Where the weapon is vehicle mounted, trials have shown that there is virtually no requirement to re-lay the weapon between rounds. New electronic sighting systems for mortars are available today to replace the optical systems, but are only in limited use. These are normally based on the mortar gunner ‘zeroing-out’ the visual display to place the weapon at the correct bearing and elevation. Similar systems were initially designed for field artillery. The introduction of digital fire control systems that include radios and display units on, or at the weapon, are expected to be the driver for these more simplified ‘sighting’ systems.

Accuracy—weapon and target location

Traditionally, the location of the mortar weapon or section has been calculated by the Section Commander / Section Chief, using a map and compass. This may have been accurate to better than 100m, but conversely may well have been out by many hundreds of metres.

Without accurate information on the observer’s exact location, it is almost impossible for an accurate target location to be calculated. Many armies have now introduced laser range finders to assist observers in producing accurate target data. However these tools are only an aide, and are reliant on the observer achieving an accurate location of his own position.

The introduction of GPS and/or inertial positioning systems are producing an accuracy of better than 25m for own position, whether that is the centre of the mortar firing position, an individual mortar weapon, or an observation post. The allocation of these equipments is an issue for individual users, but they will greatly assist in the delivery of accurate mortar fire.

Accuracy—weapon pointing

The prismatic compass, which is the standard instrument for obtaining pointing information within mortar and artillery units, has an accuracy of ±20 mils. At the maximum range of the L16/F2 81-mm mortar (5.6 km) this will place the first round at least 100m from the target, even before other issues, such as mortar and target location errors or meteorology, are considered. A GPS-based pointing system will typically provide pointing data at ±2 mils. With modern long-range 120-mm mortar systems, this should ensure that any pointing inaccuracies in the error budget are within the 50% zone of the weapon system at maximum range.

Accuracy—meteorology

Met data has been included in the ballistic calculations for artillery systems for many years. The benefits of using met data in the calculations for mortar systems is also well known, however this has only rarely been possible due to the lengthy process for entering such data into the hand-held ballistic computers (calculators) which have been used for this purpose during the last 25 years. The only exception has been where heavy mortars have been used by close-support artillery units that have been equipped with artillery fire-control computers.

The introduction of digital fire control systems, which provide a common architecture for all indirect fire platforms, will for the first time provide mortar units with access to reliable met data through the artillery communications system.

Improved range

The maximum range that can be achieved by a weapon system, and family of ballistic ammunition, is a function of the projectile weight and muzzle velocity. For a given bomb mass, the muzzle velocity can be increased by increasing the charge weight or by using a longer barrel, thus increasing the time and distance the propelling gases are able to work on the base of the projectile—increased ‘stroke length’.

The drag coefficient, related to the shape of the bomb, has an effect on how far any specific projectile will actually travel. Increased drag will automatically reduce the maximum range that can be achieved. As an example, the old 81-mm M43 ‘tear drop’ shaped bomb used in the US M29 81-mm Mortar is unlikely to achieve any major increase in range from 3,890m, no matter how much extra propellant is used, purely because any increase in velocity will automatically increase the drag.

Barrel length

A number of specialist ‘long-range’ 81-mm mortar weapon systems (barrel length around 1.8m) have been developed, with their own long-range ammunition families. These weapons have a backward compatibility with earlier standard ammunition that has been used in shorter barrelled weapons (nominally 1.2–1.4 m). When firing standard ammunition in long-barrelled weapons, the muzzle velocity, and therefore the range, will only be increased by a limited amount, because the ‘all burnt’ position of the charge system has been designed to be close to the breech in the shorter barrel. Thus the charge system will not be optimised for use in the longer barrel.

As an example, the US Army M933 120-mm HE bomb has a range of 7.2 km from the M120 120-mm towed mortar which is fitted with a 1.8-m barrel. When this round is fired from the RO Defence 120-mm AMS, which has a 3-m barrel, the maximum range is only increased by about 500 m. The 120-mm AMS has a range of about 9 km when using its standard high-pressure ammunition.

Increased charge weight with standard ammunition

Most mortar systems are developed using barrel, projectile and charge systems that are matched to a user or manufacturer’s requirement. A limited increase in charge weight can be expected to produce an increased muzzle velocity and therefore range, as is demonstrated during weapon proof testing. Before changing the charge weight in an effort to increase the maximum range, a number of system issues should be considered:

• strength of design of the barrel—will the increased charge weight over-match the barrel and potentially cause the barrel to fracture;
• increase in blast over pressure—effect of blast on the crew and other material close to the weapon; and
• strength of design of the bomb body—can the bomb body, payload and fuze safely accept the increased ‘g’ forces.

Rocket-assisted projectiles

Rocket-assisted projectiles (RAP) have been available, for many years, to extend the range of artillery systems. For these projectiles, the size of the rocket motor is usually relatively small in relation to the overall size of the shell. The increases in range and velocity for these spinning shell natures is also relatively small—range increases are in the order of 25%, while increases in velocity are around 15%.

The integration of a rocket motor into a mortar bomb is more complex. The configuration of smoothbore fin stabilized mortar bombs, with the main propelling charge surrounding the tail boom, that already contains the primary initiating charge, makes the task of designing a ‘conventional’ rocket assisted bomb, where the venturi is behind the fins, almost impossible. To date there is no record of a similar design going into volume production.

US Programmes. In the United States, Picatinny Arsenal have carried out considerable research into developing an extended range cargo bomb, XM984, with the objective of delivering a 40–66% increase in range over the standard M933 HE bomb. The tail boom is fitted with spring loaded exterior fins, which are deployed on shot exit, and the rocket motor and nozzles are fitted within a composite material ogive forward of the payload. The concept includes a velocity-measurement/rocket-ignition (VM/RI) system which will initiate the motor at exactly the correct moment, thus improving the control over the delay and burn time of the rocket motor and thereby reduce the errors in range caused by variations in velocity increases. This programme has currently slowed due to funding issues.

French Programmes. TDA in France have developed and delivered a rocket assisted high explosive bomb for the family of ammunition used with their rifled mortar. The PR PA HE bomb has been specially designed to provide a range of 13 km. From inspection of sectionalised rounds the payload appears to be reduced by up to 50%, which would normally mean a sizeable reduction in the overall lethality of the round, but the writer has not been able to verify these figures with the company. The increase in standard deviation for line and range has similarly not been disclosed, but from a comparison with other assisted spinning rounds, is expected to increase considerably.

New weapon systems

New heavy-turreted mortar systems are now available using barrels that are 3m or longer. Fitted with recoil systems to reduce the peak firing loads, these barrels can now be stronger—and heavier—to utilise new very high-pressure ammunition systems, which develop muzzle velocities greater than 400 ms^-1 in comparison with standard ammunition. Fin-stabilized projectiles should be designed for effective flight at either subsonic or supersonic velocities, otherwise they are likely to be inconsistent. Considerable development is therefore required to optimise the shape of these new projectiles. Where a bomb has been designed for maximum efficiency at sub-sonic velocities, the continual increase in charge weight will have a diminishing benefit due to the increased effect of drag in the supersonic region.

It is worth noting that as muzzle velocity increases, the potential damage to crew and material from blast also increases. Therefore the integration of new mortar weapon systems into turrets will provide the additional benefit of a reduction in the effect of blast, whilst providing a usable increase in muzzle velocity and therefore range.

In a move to deliver an immediate high rate of fire, Patria-Hagglunds have developed their AMOS system to meet the operational concepts of their Nordic customers by integrating two smoothbore mortar tubes, in a common cradle, within an armoured turret. To provide an increased rate of fire, an automatic loader has been fitted in the turret bustle with a capacity of 30 rounds. Before firing can commence, the charges and fuzes must be set. A loader-assist mechanism is fitted to the breech for use with hull stored ammunition. Patria-Hagglunds have been awarded development contracts by both Finland and Sweden for AMOS variants of both CV90 and the new Patria Armoured Modular vehicle, both of which are expected to have chassis payloads of 9–10 tons in a gross vehicle weight of about 24 tons.

New ammunition natures

Terminally guided artillery shells have been in service for many years, but most were developed to meet the Cold War threat from massed armour. These spun-carrier shells would eject their ‘smart’ payload at a suitable height, which would then autonomously acquire and self steer the warhead onto the target. In today’s less-dense battlefield it is more important to achieve precision on specific point targets than to attack unspecified armoured targets.

Similarly, early developments of fin-stabilized terminally guided mortar bombs (TGMB) were also designed to defeat ‘massed-armour’ targets. Having acquired the target, from within the search footprint into which it was launched, the seeker will guide the complete projectile onto the target. The 120-mm Strix projectile, which is fitted with an infrared seeker, is in service with both Sweden and Switzerland.

In the United States, the Precision Guided Mortar Munition (PGMM) is being developed to provide a precision mortar projectile with a man-in-the-loop acquisition system, for use within the infantry battalion. In addition to the laser seeker, there will be a second infrared seeker, which will detect and track moving targets emitting infrared radiation. This second seeker will function autonomously when no laser signal is detected. The PGMM is designed primarily for the defeat of hard materiel targets such as bunkers and buildings, although it is expected that an alternative anti-armour warhead may also be developed.

Munitions containing both spun and un-spun bomblets have been in service for many years with cannon and air delivered bomblet dispensers. More recently, un-spun bomblets have been re-packaged into 120-mm mortar carrier bombs. The aim of the development has been to harness the increased lethality of the dispersed bomblets, whilst providing the 120-mm mortar with a lightweight anti-armour capability. Studies have shown that for the same number of bombs fired, the lethality of the cargo rounds is increased by about three-fold, in comparison with a similar number of high explosive bombs. The introduction of a self-destruct function into the bomblet fuze will enhance the potential employability of these projectiles. However, their use is still clouded by political concern, especially after the Ottawa Convention on Landmines and the bad publicity that air-delivered bomblet munitions have continued to receive during operations in the Former Republic of Yugoslavia and more recently in Afghanistan.

Direct Fire. Turreted mortar weapons have introduced the possibility of using fin-stabilised mortar bombs in the direct fire role against static non-vehicle targets. Large-calibre HE mortar bombs are not designed for use in the direct fire role, but the new high velocity bombs provide sufficient consistency at ranges of greater than 1,000m for their use to be considered a benefit. Until an improved fuze with a graze action becomes available, there will always be the possibility of blinds and ricochets, as standard point-detonating fuzes may not always function against vertical targets. Additionally, some suppliers are considering the development of specialist direct-fire rounds for use against certain categories of target.

Electronic and c4i systems

Electronic systems providing ballistic calculation, position and pointing information (survey) and fire control have been available to artillery forces for many years. During the last ten years, trials in the UK, and other countries, have demonstrated the importance of mortar line survey and target location, whilst linking the observer and the mortar position with digital communications to reduce many of the inaccuracies in mortar systems described above.

Position and pointing systems

The improvements that these systems can provide have been described above. Although many countries have introduced GPS-based systems, the US Army Mortar Fire Control System (MFCS) will include an inertial reference unit (IRU) being permanently strapped, via a buffered platform, onto the 120-mm mortar barrel, to provide information for both vehicle navigation and weapon pointing.

In turreted mortar systems and some recoiled base-mounted systems, the IRU may be integrated directly onto the trunnions (pivots) of the cradle, or fitted elsewhere in the turret and sensors fitted to the cradle to provide a direct feed to the gun-control equipment.

In these modern weapons systems, the position and pointing systems are linked directly to the Fire Control System to support the accurate calculation of ballistic firing data.

Ballistic calculation

Lightweight, handheld programmable computers started to replace the ubiquitous plotter board more than 25 years ago. Most of these systems used a series of electronic ‘look-up’ tables, similar to a hard copy of the Range Tables, to calculate the firing data. These calculators were normally operated at the command post and provided only a limited improvement in capability. In the future, these computers will most likely use a Point Mass system, with 3 degrees of freedom for smoothbore mortar ammunition, similar to artillery systems but without the requirement to include data for yaw in the calculations. This is expected to provide a much more flexible calculation system and allow for update in the field when non-standard ammunition is delivered. The integration of a ballistic module with the on-board survey capability will provide the ability for mortar systems to operate autonomously when linked with digital communications.

Fire control system

The use of a Fire Control System (FCS) including a Gun Control Equipment (GCE) linked to a set of weapon drives is probably only possible in turreted or recoiled base mounted weapons. The FCS will provide both the ability to calculate the ballistic firing data—charge, bearing, elevation and fuze setting—for each target and the input data for the drive system to point the weapon at the correct bearing and elevation. Additionally, the GCE will also compensate for cant and tilt, thus removing the requirement for the mortar gunner to cross-level, as in the ground-fire weapons.

Mobility

The primary improvements being considered under the mobility headline relate to the time required and inaccuracies caused by ground firing of mortar weapons and those concerning the ability of current outdated mortar carriers to maintain the fire support to the supported unit.

The arguments for, and methods of, raising the weapons off the ground were discussed at length under Firepower above. The integration of weapons onto/into a chassis provides a firing platform that will also provide mobility. During the Gulf War, many allied mortar platoons were almost ‘neutralised’ by their inability to maintain a suitable cross-country speed to keep up with the remainder of the battalion.

To provide mortar weapon systems that are able to provide the required level of support, they should be integrated onto or into vehicles with similar mobility characteristics to the vehicles of the supported units. It is quite possible that, as in the past, future mortar systems will be integrated into in-service vehicles. As long as these chassis have received an automotive upgrade to provide comparable mobility characteristics, there should be no problems with that vehicle operating in a unit containing the most modern armoured vehicles in the world.

Protection and survivability

As with mobility, the mortar platoons in most armies are currently equipped with some of the most poorly protected vehicles in comparison with their supported units. During the Gulf War, the mortar platoons of the allied armies were the only vehicles in the direct fire zone that had no overhead cover or NBC collective protection. As such many of the mortar crews felt very exposed to the effects of counter bombardment, but more importantly to the possible effects of CB warfare.

The survivability of mortar platoons will be considerably enhanced by the introduction of improved mobility and many of the electronic systems discussed above. These will provide the ability of individual mortar platforms to operate ‘shoot and scoot’ tactics by delivering neutralising fire and then moving before the enemy can retaliate with fire. However, there will be many times when mortar platforms will not be able to move as their supported units may be at a crucial part of their battle and still require dedicated fire support. In such circumstances, it will only be the dedication of mortar crews in open topped mortar vehicles that will maintain the fire on the enemy targets.

Alternatively, the mortar weapon may be integrated into a turret that can provide the weapon and crew with a similar level of protection to the chassis and the remainder of the battalion direct-fire zone vehicles. This configuration provides the mortar crew with a comparable level of protection and survivability to the remainder of force. However, the relationship between the chassis gross vehicle weight (GVW) and possible payload, which must include the total weight of the turret and on-board ammunition, is crucial. There is a limited weight available for all equipment added to the basic chassis and a trade-off between additional protection and on-board ammunition must be carried out jointly by the manufacturer and customer.

Conclusions

Improvements in weapon and target location and weapon pointing, when allied to similar technological improvements in the consistency of mortar systems are now providing weapon systems that will deliver an accurate first round for effect in all operational theatres. When overarching indirect-fire C4I systems are superimposed on these technical improvements, mortar systems will provide the future rapid reaction forces with mobile, lethal offensive support units. The introduction of turreted mortar systems will in addition provide the unit commander with a total direct/indirect fire-support system.

Major (Retired) Jonathan Pape attended the Royal Military Academy Sandhurst 1970-1972. He served as an officer in the Parachute Regiment where he commanded a mortar platoon and later a support company. A qualified weapons staff officer, he was posted to the Infantry Trials and development Unit at Warminster before retiring in 1992. He is now Marketing Manager Combat Systems for BAE Systems, RO Defence.