Mortar ammunition update. (Technology).

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.

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Mortar bombs have been provided with larger and more lethal payload potential in addition to that all-important combat necessity of further-reaching range. With these enhancements have come changes to make the mortars more portable and handy. All these enhancements have combined to result in a shift of emphasis within the infantry mortar world.

The enhancements covered here relate mainly to infantry mortars, although it has to be mentioned that within many armed forces the larger-calibre mortars are regarded as the remit of the artillery. This is understandable with calibres such as 160 mm (still favoured by Finland and Israel), and not forgetting the retention of 240 mm mortars for special urban warfare fire missions by the Russians and a few other former Eastern Bloc nations, but 120 mm remains the largest widely deployed calibre. Some armed forces still regard the 120 mm mortar as an infantry weapon while others consider that it should be the responsibility of the gunners. Yet it is with 120 mm that the most significant recent innovations have been witnessed.

Guidance

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. While they are no longer completely novel, few mortar-related autonomously guided projectiles have yet to be rated as combat ready. Guidance will usually be found in the larger calibre category, not so much because of the required diameter to house the electronics (this is no longer an issue today) but more due to the fact that whether used in a small or a large calibre, its cost will be similar; in other words, if it is going to be expensive, one may as well invest the capability in the most effective type. This outlook is probably one of the reasons the demise of the British 81mm Merlin came about.

The first (and to date, the only) contender to achieve that accolade is the Swedish Saab Bofors Dynamics Strix. The Strix dates its concept origins back to the early 1980s with its production beginning in 1994; yet the only known takers thus far have been Sweden and Switzerland. The Strix is an autonomous munition, primarily intended for delivery against armoured vehicles, for which it is provided with a shaped charge, armour-defeating warhead.

The seeker system is infrared based but contains all manner of refinements such as comparative algorithms of potential targets to select and accurately guide the projectile down onto the target's top armour. Prior to launch some target data is programmed via a hand-held unit into the Strix so the target seeker can be activated at the right time and when pointing in the correct general direction. In-flight trajectory corrections are introduced by actuating up to twelve small, individually fired, thruster rocket motors place around the projectile's centre of gravity which nudge it towards the intended target during the dive phase of the flight. All this without intervention by the mortar men after the Strix has been fired from any existing 120 mm smooth bore mortar, including self-propelled systems.

The Strix has a range of up to 7500 metres once a sustainer motor unit has been added to the usual propellant charge. Range without the sustainer unit is up to 5000 metres. This range performance was one of the reasons why it did not meet a US Army specification for a 120 mm Precision-Guided Mortar Munition (PGMM) issued back in the mid-1980s. They anticipated a maximum range of around 15,000 metres, without the need for a sustainer unit. The result was the XM935.

The XM935 PGMM started life during the mid-1970s as a German Diehl project relating to an autonomously guided mortar projectile known as the Bussard (Buzzard). Although promising, the Bussard ran out of development funding after a few years, only to be revived when the US Army PGMM requirement was issued. Diehl Munitionssysteme teamed with Lockheed Martin Missiles & Rockets to continue the development that the Bussard then required, leading to a further development contract issued in 1995. That development phase is still not fully complete, although it is in its final stages.

The Bussard had to jump through a considerable number of technical hoops to reach the XM935 stage, the intention was to fire the projectile from the US Army's 120 mm M120/M121 mortar system. Guidance can be selected from two methods. The autonomous mode relies on a nose-mounted, infrared seeker operating as the projectile glides towards its target. Trajectory corrections are introduced by pop-out tail fins, the main fins acting as aerodynamic surfaces to create the lift that enhances the possible range. A second option is to introduce a man-in-the-loop mode where the target is illuminated by a laser designator, further guidance coming from a Global Positioning System receiver. For this mode the infrared seeker not only detects and homes using the laser radiation reflected from the target but can also home onto self-generated infrared radiation emitted from a target.

Once on target the tail-located shaped-charge warhead creates armour-penetration and fragmentation effects, the warhead being the same as that for the Dynamit Nobel Panzerfaust 3 anti-armour weapon system.

One remaining challenge for the Lockheed/Diehl team could impact on any future export sales. The US Army has asked for a unit price of under $ 20,000 per round. If past experience is anything to go by, that sum will no doubt be exceeded.

The Strix and the XM935 have now been joined by another guided 120 mm candidate, this time from the KPB instrument Design Bureau of Tula, Russia. This is the Gran (Facet), a laser-guided projectile fully dependent on a ground-based laser target illuminator. In appearance the Gran looks, before launch, more like an elongated artillery projectile rather than a mortar munition. Once in flight main and canard fins pop out, the canard fins introducing the trajectory guidance control. The laser sensor is located in the nose.

The KBP Gran, on the other hand, is also guided, but by a laser target designator, which would usually be aimed by a forward observer on the ground. The Gran, like the Strix, is designed to attack pin-point targets, but that need not be specifically vehicles. Since, as said above, it is guided by a laser mark which is picked on the descending phase of its ballistic trajectory by the semi-active laser homing sensor, it can be used for area coverage from a range of 7000 metres to treat any designated target, and this includes guerrilla detachments and terrorist caches. When one remembers that it carries an 11.2-kg explosive/fragmentation warhead housing 5.5 kg of explosives, one realises the potential of such a weapon. In fact, the Russian manufacturer says it has the destructive power of a 155 mm howitzer shell, and that its lethality still remains at attack angles of 45 degrees.

The Gran can be fired from any 120 mm smoothbore mortar, although it is being marketed in conjunction with the 2B11M mortar. In fact, KBP has devised a package that enables the entire system to be carried to the remotest places with a high-mobility Gaz Tiger 4 x 4 vehicle. The round actually has a range of 9000 metres but this is reduced to 7000 metres against static targets by the performance limitations of the laser target designator. This is further reduced to 5000 metres if the target is moving. The system, in addition to the launcher and bomb, also includes automated fire control, which incorporates both the laser designator (and rangefinder) and a thermal imager. The latter can be seen in operation at the bottom left of the KBP artist's impression in this article's lead picture.

Little has been heard of late relating to a further Russian mortar related guided projectile. This is the 240 mm 3F5, originally marketed by JSC STC of Moscow. The 3F5 was developed for the heavy 240 mm mortars still retained by the Russian armed forces and relies on the passive laser guidance principle as used with the Gran. However, the trajectory correction system is quite violent, as it does not start until the projectile is as close as 400 metres from the target. A series of small rockets are then initiated in sequence to rapidly direct the projectile towards its target. The maximum possible range of the 3F5 is 9500 metres although, as with the Gran, this is limited to 7000 metres by the performance limitations of the laser target designator. The explosive content of the warhead weighs 21 kg, making the 3F5 eminently suitable for the standoff demolition of heavy structures.

Aced

Although their carriers are not guided projectiles, smart autonomous target seeking submunitions have also entered the 120 mm mortar projectile armoury, albeit still in the concept definition stage. Although some other designs are no doubt under consideration, only TDA of France has actually marketed such a munition, the 120 Aced cargo projectile, to be available for both smooth-bored and rifled 120 mm TDA mortars, their maximum range fired from the TDA rifled mortars is 7500 metres.

A 120 Aced cargo projectile contains one or two Aced smart anti-armour submunitions, each 100 mm in diameter, weighing from four to five kilograms and employing millimetric-wave radar and infrared sensors to scan a ground area covering over 20,000 square metres for armoured targets as it descends suspended under a parachute. This happens after the 120 Aced cargo projectile's time fuze functions at a pre-selected point above a target. Once the Aced is in position and at the correct height it fires an explosively formed penetrator warhead downwards to employ its kinetic energy to penetrate a target tank's top armour. Similar Aced submunitions can be carried in various artillery or rocket projectiles with calibres of from 105 mm upwards.

TDA has teamed with Aerojet to develop a smart submunition based on the Aced and which can be fired from 120 mm mortars. It should be noted that the TDA 120 2R2M rifled mortar forms part of the Dragon Fire remotely operated mortar system under development for the US Marine Corps. This advanced concept programme is focused on using unmanned airborne platforms to seek targets and automatically direct mortar fire, all without human intervention other than target selection.

Smaller

Moving from the 120 mm down to the smallest standard calibre we meet the crew-portable 60 mm light mortars. A few 50 or 52 mm so-called commando mortar types may still be encountered but for most infantry forces 60 mm is by far the most common. Here there are two detectable trends; increases in range and enhanced on-target effects.

South Africa can provide an example of how 60 mm projectile maximum ranges have been transformed. A conventional 60 mm Type M61 high explosive bomb produced by Naschem can be fired from standard 60 mm mortars to a maximum range of 2100 metres. By contrast, a Naschem streamlined bomb fired from one of the latest long-barrelled, long-range mortars, such as the Vektor M6 system, can reach 6180 metres.

The long-barrelled mortars inflict few insurmountable weight or portability problems compared to their shorter-barrelled equivalents, the potential range improvements have therefore attracted a great deal of interest. When the longer range is combined with improved high fragmentation body materials, further on-target improvements appear. The quoted long-range Naschem example uses a special cast iron for the body, although many other similar projects utilise high grade fragmenting steels. One of the latest South African 60 mm long-range bombs can scatter fragments over much the same casualty-inducing radius as an 81 or 82 mm bomb. The introduction of a proximity fuze, such as the Fuchs Electronics M9327, to create air bursts above a target area further increases the possible lethal fragmentation radius.

Not surprisingly, some armed forces are now contemplating the conversion of their standard battalion or even company level mortar assets down from 81/82 mm to 60 mm, with all the mortar and ammunition portability advantages that can be provided by the smaller calibre. The South African National Defence Force has already decided to adopt such a policy. Several other mortar and mortar ammunition producers, such as China (Norinco) or Israel (Soltam), also offer extended range 60 mm mortar systems. TDA of France was one of the pioneers of 60 mm long range mortar developments. At one time the former Yugoslavia was another exponent of long-range mortar and projectile innovations although, understandably, little has been heard from them of late.

Enhanced on-target performance also arises with another relatively recent 60 mm mortar projectile development, the Ruag Ammotec Mapam that qualified for the Swiss Army's Model 87 mortar during 1995. The 60 mm Mapam has a streamlined outline and a thin-walled body. The explosive content is Composition B, or impact and heat insensitive PBXN-110 high explosive, around which are located 2500 steel spheres held in an epoxy resin matrix. This controlled pre-fragmentation feature ensures that the anti-personnel effects of the Mapam are greater than those of comparable conventional bombs by a factor of between 1.2 and 5. In practical terms this means the Mapam has the same lethal on-target effects as a conventional 81/82 mm bomb. The maximum range performance depends on the type of mortar and propelling charges involved, but is typically 3500 metres, although up to 4000 metres has been mentioned. One last point about the Mapam lies in its hyper sensitive fuze, which will trigger off the warhead as soon as it comes into contact with the softest surfaces, like snow.

The Mapam has been test fired by the US Army's M224 lightweight mortar, resulting in full-scale qualification and type classification for this mortar. It can also be fired from the ultra-light 60 mm commando mortars available from many manufacturers.

Cargo

Ruag Ammotec also features in another mortar projectile innovation area, the cargo projectile carrying all manner of submunitions (such as the aforementioned Aced), although mainly concentrating on dual-purpose bomblets. This form of projectile has been around for some time; some observers include illuminating flare bodies in this category. The unfortunate British 81 mm Merlin project, now long since defunct, demonstrated that only mortar projectiles of 120 mm and upwards could carry and dispense a viable quantity of useful bomblets to the required combat ranges, so available models are confined to the 120 mm calibre. One exception is Pyrkal of Greece who offers its 107 mm (4.2-inch) HE GRM20 rifled cargo round which contains 20 pre-fragmented steel bomblets.

The Ruag 120 mm cargo projectile is based on the Israel Military Industries (IMI) M971/1 design. It dispenses 32 dual-purpose bomblets, each almost certainly based on the IMI M85 with its now obligatory self-destruct function should the impact fuze fail to function. Each bomblet can penetrate up to 69 mm of armoured steel while scattering lethal fragments over a nine-metre radius.

Another advanced 120 mm cargo projectile is the Mat-120 from Instalaza of Spain. Here the emphasis is on electronics, although there is no stored energy within the projectile or its contents during storage or handling and no maintenance is required. An electronic time fuze in the projectile nose initiates the dispensing of the 21 dual-purpose submunitions. Each submunition has its own electronics-based safety and arming system with a self-destruct mode should they fail to detonate as required on impact. If the self-destruct mode also fails to function for any reason a self-neutralisation mode is also provided. Each Mat-120 bomblet can penetrate up to 150 mm of steel while scattering effective fragments over a 15-metre radius. A full Mat-120 bomblet payload can cover an area of from 2500 to 3500 square metres and create approximately 13,600 effective fragments. Its maximum range is 5500 metres.

A further 120 mm cargo projectile in the pipeline for the US Army's M120/M121 120 mm Battalion Mortar System is the rocket-assisted XM984. Although no firm conclusion has apparently yet been reached, General Dynamics Armament Systems expects that the XM984 will have a range of between 10,000 and 12,000 metres, compared to the 7240 metres delivered by the other conventional and Israeli Soltam-derived projectiles in the M120/M121 ammunition suite. It is planned that the XM984 will carry 54 XM80 bomblets, each with its own all-important self-destruct mechanism. Also planned is that the XM984 will have a composite materials body, while the range-enhancing rocket motor will be located in the nose area to avoid any interference with bomblet dispensing through the body base area.

81/82 mm

Compared to the developments outlined above, 81/82 mm mortars have undergone improvement to a lesser extent. The long-range mortar barrel and the streamlined projectiles have featured once again with the French TDA models such as the MO 81 LP and South African Vektor models in the vanguard. Norinco of China has introduced its own long barrelled mortar in the form of the 81 mm Type W87 (the 82 mm model is the W84). A family of special streamlined Type W87 projectiles was developed for this mortar, providing a maximum range of 5700 metres with a special charge. For a comparison, earlier Soviet-derived mortar equivalents could deliver ranges of up to just over 3000 metres. The exact service and manufacturing status of the W87 system is currently uncertain although it appears to be still on the market.

One of the minor mysteries of the current Russian mortar scene is that they have yet to reveal whatever innovations they might have made in the performance enhancement area. While streamlined 120 mm projectiles have appeared, there is no sign of similar innovations in the 82 or 81 mm calibres. Eastern Bloc 82 mm projectiles continue to display their pre-1939 origins by retaining poorly shaped blunt outlines, manufactured using cast iron of dubious fragmentation quality. The maximum range that can be achieved by their latest 82 mm 2B14 Podnos mortar is 4270 metres at best, much of that range being introduced by adding extra propelling increments. By contrast, the British 81 mm L16A2 mortar (and its close cousin the US 81 mm M272) can reach a respectable 5700 metres. At one time it was anticipated that further British mortar and ammunition developments could increase L16 series ranges to over 7000 metres, at least. It may well emerge that this improvement programme has been sidelined in favour of more drastic developments, probably involving 120 mm systems.

Another Russian mystery is that although they have introduced advanced mortar systems such as the 82 mm AM 2B9 automatic mortar which produced such a stir when it was first observed during the late 1970s, there is no indication of any similar current developments. They appear to have taken the view that 120 mm is better, their 120 mm 2S11 Sani mortar delivering heavy (the HE-Frag projectile weighs 16.7 kg) streamlined projectiles to over 7000 metres, similar to equivalent 120 mm mortars fielded by the Western Bloc. The US Army has made the same decision. All further 81 mm ammunition development has been placed in abeyance in favour of the 120 mm M120/M121 Battalion Mortar System. The M120 is the ground-based model--the M121 being self-propelled on modified M113 armoured personnel carrier platforms.