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FUTURE MORTAR SYSTEMS RADOŠ RONČEVIĆ

Military Technical Institute, Belgrade, roncer@eunet.rs

MIRKO JEZDIMIROVIĆ, MIODRAG LISOV

Military Technical Institute, Belgrade, ejezdimi@ptt.rs

ANA BRKUŠANIN Technical Test Center, Belgrade, ana.brkusanin@gmail.com

Abstract: Operations in Afghanistan have highlighted the necessity for militaries to possess responsive organic fire-support in demanding operating environments. Meanwhile, recent advancements in precision guidance technology, target acquisition and fire control systems have hugely improved the capability and employability of the mortar in fire-support missions, especially where collateral damage is a major concern. Militaries globally are beginning to recognize the mortar can provide unique, prompt and precise indirect support to a ground commander and discover where future capabilities lie. This article is also about of current lightweight systems (60 mm and 81 mm), extended range capability, increased mobility and lethality and latest mortar systems of US Army, US Marine Corps, Swedish Army, French Army and Russian Army. It offers a short insight into the latest technologies and tactics that will revolutionize the use of light, medium and heavy mortars.

Key words: mortar systems, self-propelled mortar 120 mm, ammunition, laser and GPS guidance. 1. INTRODUCTION

According to general doctrine, the mission of the mortar platoon is to provide close and immediate indirect fire support for the maneuver battalions and companies.

Mortars were evident amongst the first artillery weapons. The earliest examples were clumsy, short-barrelled weapons firing metal balls. Even after the design and manufacturing techniques for guns began to improve, mortars continued to be used. Their employment varied with calibre, but essentially they were used to lob projectiles on top of the enemy or to breech fortifications. The characteristic that distinguished mortars from guns was that they were always fired at elevations of 800 mils or greater. It is this characteristic (Fig. 1) that still identifies a modern mortar from a gun or howitzer, regardless of whether the mortar is breech or muzzle loading, or whether the bore is smooth or rifled.

The advantages of a mortar system accrue primarily from the comparative simplicity of the system. The main components of a mortar are the baseplate, the barrel, the bipod and the sights.

A typical ground-mounted mortar today is very similar to the original Stokes 3-inch mortar produced for the British Army in 1915. At first sight the world of the infantry mortar and its ammunition is one where little seems to

happen. A close examination of any current mortar will reveal few fundamental changes from the basic concept of the high angle, high explosive delivery tube system introduced to the modern battlefield by Sir Wilfred Stokes back in 1915. But much has changed during recent years.

Figure 1: Shells trajectory

Sir Wilfred Stokes would still recognize the outlines of his original design in today's mortars. What he would not recognize is their current firepower and range potential, the diversity and performance of the ammunition appearing on the scene, and the complexities of the mortar fire control systems now available.

2. NEW MORTARS

The US is developing a lightweight 81 mm mortar (Fig. 2). The M252A1 81 mm mortar weighs 31.9 kg with a 13.7 kg barrel, 8.2 kg bipod and 10.0 kg baseplate. The

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threshold target is a 28.99 kg weapon with a 11.11 kg barrel, 8.57 kg bipod and 8.26 kg baseplate. The more ambitious objective target is a 24.85 kg weapon with a 9.53 kg barrel, 7.35 kg bipod and a 7.08 kg baseplate. In order to reduce weight the army is evaluating the suitability of Inconel 718, a nickel-based alloy, for mortar tubes, carbon fibre reinforced composites for baseplates and a lightweight material for a new bipod. Although Inconel 718 has never been used before to produce a gun barrel, tests to date have shoun its ability to retain high strength at high temperatures. Nothing was noted to preclude the use of Inconel 718 in future mortar designs.

Figure 2: Current and lightweight 81mm and 60 mm US mortars [1]

Two baseplate designs are being evaluated: a carbon fibre reinforced thermoset composite design that offers a 40% weight reduction, and a high strength forged aluminium baseplate that is 25% lighter. A carbon fibre reinforced thermoplastic baseplate was eliminated at early stage of the test process. An aluminium matrix composite prototype baseplate will also be tested.

Figure 3: "A-mount" bipod design [1]

The L16/M252 K-mount bipod design will be replaced

with a more conventional A-mount design (Fig.3). Two designs made of composites, plastics and lightweight metals have undergone initial firing tests, and a rough handling and user evaluation took place.

The objective weapon should have a unit price not exceeding the $ 70,500 cost of an M252. The objective weapon requirements are similar to the M252 in other respects - the same 83 m minimum and 5935 m maximum ranges, the same 30 round-per-minute maximum and 16 round-per-minute sustained rate of fire, and a tube life equal too or greater than the present 10,000 rounds. In the future the army is seeking an FCS Non-Light of Sight Lightweight Dismounted Mortar System that combines a 50% weight reduction with greater range and lethality.

At the bottom end of the scale, where extreme portability is the primary consideration, simple 51mm or 60mm Commando mortars continue to be used to provide high-explosive (HE), smoke or illuminating fire support, complemented by grenade launchers 30mm or 40mm. Customarily such mortars give ranges of 1000 to 2000 m for weights of between 7 to 15 kg, though greater ranges are now technically possible. For example, the South African Vektor 60mm LR mortar system puts 2.4 kg low-drag bombs on targets out to 6180 m, though to this a strengthened bipod and a baseplate from an earlier 81 mm mortar are used, taking system weight to 24 kg.

The most favored and widely used caliber for company/battalion-level fire support requirements remains 81/82mm. The W91 81mm mortar, developed in China by Norinco, has the longest range. It weighs 65 kg and has a claimed range of 8 km with a 5.72 kg bomb. The majority of older 81mm systems have a range of closer to 6 km, among them the widely sold RO L16, in service with 18 other armies, including the US Army (designation M252) [2].

The warhead delivery and range advantages of heavier-calibre mortars, 120 mm predominanting, are such that they are being widely adopted at the expense of the 81/82 mm equivalents. Heavy mortars are to the East and West with smoothbore barrel 120 mm. Exceptions are the only French weapon RT and the American system of 4.2 inches (107 mm), which are rifled barrel and use bombs with a leading pre-sliced ring (behind which there is an additional seal). In service of many countries are already self-propelled mortars: 120 mm M1064A3 U.S. - Israeli solution Cardom a modified M113 vehicle, a British FV432 81 mm, Chinese 120 mm WZ551, Russian 120 mm VENA, Russian 120 mm NONA - C, Swiss RUAG Bighorn 120 mm, German Wiesel 2 120 mm, Finnish 120 mm AMOS, Israeli 120 mm Soltam, Singapore SRAMS self-propelled mortar systems and many others. The recent years clearly points out the tendency of large-scale development of turret with one or two barrels and recoil device that allows mounting on wheeled or tracked chassis.

Time is critical when US light manoeuvre forces are in combat, and The M326 120 mm Mortar Stowage System (MSS) makes it easier for soldiers to quickly set-up and take down the M120 120 mm mortar on the battlefield (Fig. 4). Due to its weight, the 120 mm mortar

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tube takes considerable physical effort to put it in place, fire and quicqly move to avoid enemy counter-fire. The M326 will increase survivability by significantly speeding the time it takes to set up and take down a mortar system.

Figure 4: The M326 120 mm Mortar Stowage System (photo: BAE Systems)

It uses a hydraulic system to lift the fully asemled M120 mortar into and out of the trailer or vehicle used to transport the weapon. A steel strut connects the mortar to the M326 lift arm and holds the assembled mortar base- plate, tube and bipod together. The mount and dismount of an assembled M120 Mortar have been achieved in less than 20 seconds during trials.

It is useful to describe the new Russian concept, the 120 mm NONA-M1 towed rifled semiautomatic breech-loading mortar (Fig. 5). The NONA-M1 can be dismounted, without using tools, into four components convenient for installation on the vehicles or carriage by the crew in rough terrain. Small weight of the mortar combined with high efectiveness of the ammunition and good maneuverability help the mortar units avoid enemy return fire.

Figure 5: The 120 mm NONA-M1 mortar [3]

Arguably the world's most sophisticated 120 mm mortar

is the AMOS or Advanced MOrtar System (Fig. 6) developed by Patria Hägglunds. The AMOS is a turret system armed with twin barrelled, breech-loaded, 120 mm, smoothbore mortars and features a semi-automatic loading system and a fully automatic laying system. AMOS has been fitted to a wide range of armoured vehicles such as Patria AMV and Combat Vehicle 90. When fitted to a vehicle, both GPS and inertia positioning are used. The electronic fire-control system utilises digital maps. Twin barrelled AMOS is able to keep up maximum rate of fire of 16 rounds per minute [4].

Figure 6: NEMO and AMOS Patria Hägglunds systems (photo: Patria)

A key feature of AMOS is its ability to employ Multiple Rounds Simultaneous Impact (MRSI) technique (Fig. 7). This is a modern version of the earlier "time on target" concept in which fire from different weapons was timed to arrive on target at the same time. It is possible for modern computer-controlled artillery to fire more than one volley at a target and have all the shells arrive simultaneously. This is because there is more than one trajectory for the rounds to fly to any given target: typically one is below 45 degrees from horizontal and the other is above it, and by varying the amount of propellant with each shell, it is possible to create multiple trajectories. Because the higher trajectories cause the shells to arc higher into the air, they take longer to reach the target and so if the shells are fired on these trajectories for the first volleys (starting with the shell with the most propellant and working down) and then after the correct pause more volleys are fired on the lower trajectories, the shells will all arrive at the same time. This is useful because many more shells can land on the target with no warning. With traditional volleys along the same trajectory, anybody at the target point will have a certain amount of time (however long it takes to reload and re-fire the guns) to run away or take cover between volleys.

Figure 7: MRSI technique

Using MRSI feature it is posible to set upon a burst of up

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to 16 rounds. The manufacturers contend than one AMOS can produce the same effect as a platoon of four muzzle loaded mortars!

An AMOS turret has a full 360-degree field of fire and can fire at elevations between -3 to 85 degrees. The mortars can also be used in the direct fire role for defence and to engage urban target. The AMOS's semi-automatic loading system achieves a maximum rate of fire of 16 rounds and sustained raited of 14 rounds per minute. Less than 30 seconds after the vehicle halts, the first rounds can be fired and the vehicle is ready to move again less than 10 seconds after the last round is fired.

Ammunition for AMOS includes the Strix 120 terminally guided mortar bomb and the RUAG Land Systems 120 mm Mortar Cargo Bomb, which contains 32 grenades fitted with a HEAT warhed that will penetrate 70 mm of conventional steel armour. The grenades are fitted with a self-destruct mechanism. Because AMOS is breech-loading, it cannot fire standard muzzle-loaded mortar rounds. AMOS rounds feature a "short stub case" at the base of the fins, similar a sabot. In this way, expended rounds fired by AMOS can be easily differentiated from traditional mortar system.

A vehicle such as the CV90 a typical ammunition load could consist of 84 conventional rounds and six Strix terminally guided projectils.

The standard AMOS crew consists of a commander, gunner, loader and driver.

For customers requiring a less expensive system than the AMOS Partria developed, the NEMO (NEw MOrtar) 120 mm single turrel smoothbore turreted mortar, mounted on the 8x8 AMV (Fig. 6).

The 1,5 tonne turret can be installed on 6x6 shassis or a tracked shassis. The NEMO's semi-automatic loading system achives a maximum rate of fire of 10 rounds and sustained raited of seven rounds per minute. Less than 30 seconds after the vehicle halts the first rounds can be fired and the vehicle is ready to move again less than 10 seconds after the last round is fired.

3. NEW MORTAR AMMUNITION

Swiss company RUAG developed the Mortar Anti-Personnel Anti-Materiel (MAPAM) concept to provide a better fragmentation effect for high explosive ammunition. The detonation of a standard mortar bomb produces different numbers of irregular fragments that fly at different speeds. The 60 mm MAPAM round features a unique warhead body made of a matrix of 2400 ball bearings and epoxy that provides increased lethality with a predictable dispersion pattern. The US Army states "this improved ammunition provides the soldier with as much as 70% increase in lethality over conventional US ammunition" now in service. RUAG demonstrated and 81 mm MAPAM and is developing a 120 mm round.

TDA of France has developed the 120 mm Aced cargo anti-armour projectile which contains one or two Aced smart anti-armour submunitions, each 100 mm in diameter, weighing from four to five kilograms and

employing milimetric-wave radar and infrared sensors to scan a ground area for armoured targets as it descends suspended under a parachute.

The mortar has entered the world of the guided projectile, although at a considerable cost that will keep the resultant projectiles out of the armouries of many nations. In today and tomorrow's conflicts there is a greater need for increased precisision and reduced collateral damage.

Projectile guidance technology has already been used since 1994 in 120 mm mortars, with the IR homing Bofors/Saab Strix and the Eastern Bloc 120 mm Gran mortar rounds. Strix can engage targets at a range of 7 km, operates in an autonomous heat-seeking mode which can intelligibly recognize targets and discriminate target among decoys and burning target. It is optimized as an anti-armor weapon, defeating targets with top-attack.

The 120 mm Gran (Facet) laser-guided mortar projectile was developed by the KBP at Tula (Russia). It is intended for the indirect engagement of spot targets such as structures or lightly armoured vehicles by 120 mm mortars when conventional artillery assets are not available. The Gran is apparently usually carried by self-propelled 120 mm mortar vehicles such as the 2S9 Nona-S or 2S23 Nona-SVK, but could also be fired from conventional ground-mounted 120 mm mortars. Maximum range is 7500m. The Gran projectile is 1,225 m long and weighs 25 kg. It resembles an elongated artillery projectile; there are no tailfins. A laser sensor is located in the nose.

ATK company has developed the 120 mm M395 Precision Guided Mortar Munition - PGMM (Fig. 8). PGMM will not use rocket assistance for range enhancement, but utilize aerodynamic surfaces for the mid-course gliding. On the terminal phase,a semi-active laser homing seeker acquires the target and guide the munition to impact. Initial productions of the PGMM will be equipped with semi-active laser seekers, and be capable of a range of 7.5 km with 10 m CEP (Circular Error Probable). Follow-on systemswill have optional thermal imager, and extended range capability, as well as more choices for fuzes and warheads. The IR seeker will detect and classify targets, process the information automatically into navigation (GPS), guidance and control subsystems to ensure first-hit-on-target. A self-destruct mechanism eliminates the collateral damage from duds [5].

Figure 8: XM395 120 mmPGMM, [5]

General Dynamics and BAE Systems have developed and

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sucessfully demonstrated a precision 81 mm mortar based around the current UK mortar bomb, Roll controlled guided mortar (RCGM). How the RCGM works? Target coordinates are programed into the RCGM using a portable GPS setter. The fuze is set manually to proximity, point detonate or delay modes. Once the mortar is launched the on-board GPS acquires satellites and determines the mortar's position and vertical reference (up). Based on continuous GPS updates, the auto-pilot calculates corrections and sends commands to the canards to continuously maneuver the mortar toward the target. Upon impact the mortar detonates in the desired mode.

In 2012 a tactical demonstration of 16 rounds was completed, achieving CEP of less than five meters at ranges from 980 to 4000 meters [6].

4. FUTURE DESIGN THRUST AREAS

In development of the new and modernization of the mortar weapons introduced in service, the following trends emerge: − increase rate of fire, − reduce the weight and dimensions, − increase the range, − improve terminal effect of projectile, − increase the survivability and maneuverability, and − increase positioning and laying accuracy.

Rate of fire should be increased, primarily, due to installation of a semi-automatic loading device that takes the 120 mm projectile from the lower part of the mortar up to the muzzle where it is automatically loaded (Fig. 9). Faster heat dissipation occurred during the shooting at an increased fire regime is achieved by the construction of tube with external finns, which increases the external surface. Mode and rate of fire have a crucial impact on the firepower mortars. Instructions for use shall be limited to the level at which the outer tube temperature must not exceed 450K to 470K. Mode and rate of fire can be improved if the tubes are used to create materials resistant to high temperatures, with better heat exchange with the environment. Chrome tube channel has become a standard in the production of mortars of all calibers.

Figure 9: The TDA 120 mm 2R2M system with added units

Finally, devices to prevent double loading decrease psychological crew efforts, therefore increasing the speed and accuracy. New, double barrel design (AMOS), enables a target to be saturated with 26 rounds in one minute with the first 14 rounds achieving a MRSI. The usual rates of fire are: up to 20 rounds per minute for 60 mm mortars, 15 to 18 rounds per minute for mortars 81/82 mm and 10 to 12 rounds per minute for 120 mm caliber weapons.

Weight reduction is achieved by using high mechanical properties of steels and light alloys. Metallurgical advances have introduced stronger and lighter steel alloys for barrels, while light metal alloys found ideal applications in mountings and base plastes. Such materials have enabled the mortar to remain a relatively light weapon to the extent that standard infantry fire support mortars, now nearly all with calibres of 81 or 82 mm, can be stipped down for manual pack transport, even if their more usual carrier is a cross-country or armoured vehicle. An American mortar 81mm M252A1 weights 31,9 kg what is around 9 kg lighter of M252 mortar, and at the same ballistic characteristics are unchanged.

The range can be increased primarily by using AR-mines. In this way the range 120 mm mortars increased approximately 2.5 to 4.5 km. Also, the use of mines favorable aerodynamic shape and the increased charge is obtained an increase in range. The range increases demonstrated by modern mortars compared to those of only a few years ago, are considerable. For instance, the 82 mm M37 mortar, stiil widely fielded throughout the Russia and former Eastern Bloc and elsewhere, has a maximum range of 3000 m. By contrast, RO 81 mm L16A1 can reach nearly 5800 m. This is an extreme example but it does demonstrate the advances made in mortar ammunition design during recent years.

In place of the blunt outlines of the M37 bomb family, L16A1 bombs are much more streamlined and aerodynamically shaped, but retain highly effective payload capacities. They also use more advanced propellant systems - so advanced that when L16A1s are fired at maximum charge, muzzle pressures can create discomfort for crews. This has been alleviated on the US Army's version, the M252, by the addition of a muzzle cone to deflect the blast upwards. Other designs have similar attachments, such as the Russian 82 mm 2B14 Podnos (the successor to the M37) on which the muzzle attachment also prevents inadvertent double loading.

To improve terminal effect, the HE projectile body is made of malleable perlitic cast iron. This type of alloy offers more homogeneous fragmentation than steel, thus considerably increasing the projectile's effectiveness against unprotected units. Thus terminal effect of rifled mortar projectile 120 mm is comparable to a 105 mm and even 155 mm standard artillery projectile. The anti-armour projectile body is made of pre-fragmented special steel. Sheaf focusing and the high initial velocity of fragments (1500 m/s) allow for perforation of 8 to 15 mm armour plate at more than to 10 m from the point of impact (percussion fuze). Terminal effect against vehicles can be further improved using a proximity fuze. New TDA PR Cargo projectil has high penetration capability

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of the shaped charge: 125 mm or 150 mm of steel.

The introduction of "smart" technology to the mortar bomb not only results in increased hit probability: it also elevates the fire support mortar into the anti-armour weapon category, providing the infantry with a new method of attacking its greatest enemy, the tank.

The advantages of a GMA are that in ideal conditions it gives a high probability of defeating a tank with one or two rounds. By comparision up to 2000 conventional HE rounds or 250 improved conventional munitions may be needed to achieve the same result. The advantages in logistics and barrel wear are obvious. The disadvantages include: the need for some form of target designation, reduced range compared with conventional HE- projectiles, the effect of cloud cover in the area of the target, and the reliance on good communications and

response.

Survivability and maneuverability. Technology advances in battlefield surveillance systems, including mortar locating systems, have placed the mortar under increased threat of counter bombardment. To overcome this, the mortar must:

a) become more mobile - to allow a "shoot and scoot" operation (Fig. 10). The mortar takes 30 seconds to prepare for firing on coming to a halt, 60 seconds for a typical fire mission and 30 seconds to come out of the firing position;

b) offer better protection - in the form of an armoured vehicle protection; or

c) ideally, present a combination of these two points.

Figure 10: Shoot and scoot tactics (photo: RUAG)

For many armed forces, mortars will continue to be carried on light vehicles or on soldiers' backs. Armoured formations mount mortars in armoured personnel carriers, firing through open roof hatches (Fig.11). Another example of vehicle-mounted weapon is fully traversing turret (Fig.6).

Figure 11: RUAG Bighorn 120 mm self-proppeled mortar

Turret mounted mortar, as the mortar installation can be fully enclosed by armour, the crew will be proctected from shell bursts and small arms fire. They will also have protection against nuclear, biological and chemical (NBC) warfire attacks. Large barrel traverse can be introduced rapidly, especially when computer-based fire control system become involved. The barrel can also have a direct-fire capability, a feature totally lacking with the open-topped carrier option. By contrast, open-topped

carriers do not demand such complications, complications that not only add complexity but also weight and unit cost. In an era of rapid deployments by air, any weight additions have to be avoided wherever possible, one of the main reasons why the open-topped carier approach can be preferred.

Another important consideration in favour of open-topped carriers is that a conventional baseplate and field mounting can be carried and brought into action should the carrier vehicle become disabled or should the operational situation demand dismounted deployment. Another positive factor for the open-topped carrier is that it can be readlily concealed within formations of other similar carriers. Finally, the number of potentially available platforms for turreted mortars versus the base-plate type is a factor of three to eight.

Tracked mounted mortars have extra crev protection, no requirement for bedding-in, and less time used in preparation for firing. The main disadvantage is that a degree of strategic and tactical mobility is lost, particulary in terms of airportability.

Increase positioning and laying accuracy. The first point to be addressed in improving the accuracy of mortar units is the adoption of Global Positioning and Inertial Navigation Systems (GPS/INS) options to the mortar baseplate. A good example of how such technology can be integrated to the latest mortar options is the fire control system supporting the 2R2M mortar system; this not only provides continuous updating of the baseplate location, thus removing geographical errors from the fire solution, but also includes a fully integrated mortar alignment system that ensures consistency of aim after each firing. This is achieved by installing a direction and attitude

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control system on the mortar baseplate. Once the mortar is correctly aligned to the fire control solution, the processors record this and after each firing provide the crew with a visual display of any minor tube corrections that are then steered through electrical drives to return to the original firing position.

Thus, 2R2M 120 mm rifled recoiled vehicle mounted mortar achieves twice less dispersion at maximum range of rifled towed mortar or 5.6 times of smooth one (Fig.12).

Figure 12: Dispersion on the target (photo: TDA)

5. CONCLUSIONS

Whatever the caliber involved, and almost 100 years, the mortar is still a muzzle-loaded barrel (usually smooth-bored) on a light mounting frame, with the bulk of firing forces being absorbed through a base plate; and projectiles are still fired at a high angle of elevation so they descend almost vertically onto their target.

Some examples of mortars with rifled bores and breech loading mechanismes have been produced; however, they can be regarded as unortodox versions of this type of weapon. The main disadvetages of these unortodox design innovations for mortars are that they tend to degrade their rate of fire and their inherent simplicity in design. As we shall see these are two of the important characteristics of

mortars and ones that should not be discareded lightly.

For many armed forces, mortars will continue to be carried by one or more men (larger mortars could usually be broken down into components), or transported in a vehicle. Armoured formations mount mortars in armoured personnel carriers, firing through open roof hatches. Even at size (120 mm to 300 mm for heavy mortars) mortars are simpler and less expensive than comparable howitzers or field guns.

Sir Wilfred Stokes would be very impressed.

ACKNOWLEDGMENT

This work has been done within the Project III 47029 supported by Ministry of Education and Science of Republic of Serbia.

References [1] R. Ucci: US Army Mortars Update, International

Mortar Conference London, November 2010. [2] R. Pengelly: Mortars aim for more capability, Janes

International Defense Review 1/1977. [3] Land forces Systems, export catalogue,

Rosoboronexport, Moscow, 2011. [4] C. F. Foss: Jane's Armour and Artillery 2010-2011. [5] A. Cherrill: Accelerated Precision Mortar Initiative,

International Mortar Conference London, November 2010.

[6] 81 mm RCGM, Roll Controlled Guided Mortar, catalogue, General Dynamics and BAE systems, 2012.