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A survey of the modern mortar.

A Survey of the Modern Mortar

The mortar is a weapon that has been in and out of fashion during its long history, a history that can be traced back to the very early period of black powder ordinance. The mortar as we know it today was first produced commercially during the Great War of 1914-1918, and since then its basic form has remained virtually unchanged. In basic terms, it is still a length of pipe, mounted on a baseplate and bipod arrangement, into which projectiles are loaded from the muzzle and which are fired via a firing pin at the base of the tube. Both smooth-bore and rifled versions are in use, but smooth-bore models predominate.

Since the Great War, the mortar has had its periods of frantic development, followed by years during which nothing much happened in design terms. We are at present in the midst of one of the frantic development periods. All around the world new designs and variations are appearing and entering service in large numbers, and many new mortars are in the development pipeline. This is therefore an appropriate time to stand back and make an overall survey of exactly what is happening to the mortar around the world.

Types

The modern mortar falls into three easily-defined and distinct classifications - light, medium and heavy.

These three classes have been in existence for many years but to them must now be added one further class, namely the specials. Their definition will be given later for there are relatively few of them. The bulk of all mortars fall into the three classes mentioned above.

Light mortars have calibres of 51 or 60 mm, 60 mm being the calibre preferred by most armed forces. Only the United Kingdom retains in service a 51 mm (2-inch) mortar, while the 50 mm mortars once widely used by Warsaw Pact nations (plus China and Yugoslavia) have now nearly all passed from use, except in Third World or guerrilla armed forces.

Light mortars are sub-divided into two further types; "standard" mortars that come complete with base plate and bipod, and "commando" mortars. The latter are little more than mortar barrels with minimal base plates, no bipods and only rudimentary sighting systems. Both types can be carried as manpack loads, with the standard types requiring at least two men to serve the weapon in action. By contrast the commando types can be carried and served by only one man.

The medium mortar is the most widely used of all mortar types (although that might eventually change) and covers only two calibres. Virtually all nations other than the old Warsaw Pact members and their allies use the 81 mm calibre; Soviet-influenced nations (and China) retain their 82 mm calibre. In practical terms there is nothing to choose between the two since 82 mm mortars can be persuaded to fire 81 mm projectiles - although the converse is not recommended.

Medium mortars can be transported as manpack loads but the more usual method is to carry the sub-assemblies in some form of light vehicle and re-assemble them for off-vehicle use. There are also self-propelled variants normally carried inside whatever the standard armoured personnel carrier of any particular nation happens to be - some nations use light "B" vehicles for this purpose.

There are several calibres in the heavy mortar group. They start with 107 mm, or 4.2-inch. Then comes the most widely used of the heavry calibres, namely 120 mm. Above that there are 160 mm and even 240 mm mortars, but the latter two calibres are rarely encountered outside the Soviet sphere of influence.

Heavy mortars come in many forms, as will be described below, but most are towed into action and bipod-mounted for ground use or are carried on self-propelled carriages, again mainly on armoured personnel carrier chassis. The really large 160 and 240 mm mortars require a tank-sized chassis.

Nearly all mortars are muzzle-loaded but there are types that have breech mechanisms. Usually intended for employment on vehicle turrets or some form of pedestal mount, breech-mounted mortars fire ordinary mortar projectiles, and recoil forces are absorbed by springs or other recoil systems. Nearly all in-service breech mortars are 60 mm models, mostly produced by Thomson Brandt Armements of France. The same firm also produces a full range of 81 mm and 120 mm mortars. A typical example of the latter is the British Royal Ordnance 120 mm mortar intended for installation in the RO 2003 armoured mortar carrier. Little has been heard of this project recently, however.

Tactical Use

The light mortar is normally deployed at platoon or company level: in some circumstances they may even be allocated to sections. Since the small projectiles involved in the 51 and 60 mm calibres can have only limited payloads, they have correspondingly limited anti-personnel effects, often little more than like a conventional hand grenade - although delivered to considerably longer ranges. Light mortars thus have greater tactical uses as delivery systems for screening or marker smoke. Increasing in importance these days is the light mortar's ability to act as a delivery system for illumination rounds to light up and reveal armoured vehicle targets for subsequent night engagement by anti-armour systems.

Medium mortars are the work-horses of the mortar world. Deployed at company or battalion level, they act as infantry support weapons, delivering high explosive, illuminating and smoke rounds, under the control of the infantry themselves who would otherwise have to go through time-consuming communication procedures to get the artillery to carry out the same services. They can provide high explosive fire support for both attack and defence, illuminate targets for other weapons to engage, and provide screening smoke (or target marker smoke for ground attack aircraft or artillery observers). Phosphorous-filled projectiles can double either as incendiaries or smoke-producers. To these roles has been added an anti-armour potential which will be outlined below.

Heavy mortars can act as infantry support weapons under infantry control (at battalion or brigade level), or they may be placed under artillery control. In the latter case, heavry mortars are usually employed to supplement other artillery systems. Only for special roles do heavy mortars actually replace other field artillery weapons, mountain warfare mortar batteries being one example of the latter.

In the heavy mortar category the 120 mm calibre is numerically the most important by far, to the extent that it is now replacing the other calibres. Thus the Soviet 107 mm and American 4.2-inch (actually 107 mm) heavy mortars are currently in the process of being replaced by 120 mm weapons. Few nations now employ the 160 mm calibre (and then only under artillery control) while the 240 mm monsters are generally acknowledged as being too bulky and heavy to employ with any degree of facility. The limited number of 240 mm mortars still employed by the Soviet Army (the SM-240) are mounted on tracked chassis and are employed to demolish strong points and urban warfare targets. Few, if any, of the older M-240 towed mortars now remain in Soviet service.

The 120 mm mortar is gaining in general popularity by the year. Once regarded by many as too heavy and cumbersome, it has almost entirely replaced the infantry gun in many armies. In some cases, it has even replaced the divisional support field gun or howitzer. The reasons are not hard to find. In size and weight terms the 120 mm mortar is lighter than a field piece, yet it can deliver a payload at the same ranges and of the same efficiency. Being lighter than field guns or howitzers, 120 mm mortars require smaller towing or carrier vehicles, they have smaller crews, need less maintenance, and can be emplaced in positions inaccessible to field guns. Their high angles of fire are often invaluable in built-up or wooded terrain and in very broken terrain or special warfare areas such as mountains.

There are even moves in some armed forces to replace the medium mortar with 120 mm mortars. The weight of the 120 mm designs is now such that there is only a small difference in practical terms regarding weight and size, yet the 120 mm projectile can carry a proportionally much larger payload. A typical 81 mm projectile contains 0.68 kg of high explosive filling, for example, where the corresponding 120 mm filling is about 2.3 kg.

Although traditionally the mortar is a smooth-bore weapon, some 120 mm designs feature rifling. They are loaded and handled in much the same way as conventional mortars but claim improved accuracy. On the other hand, their projectiles are more difficult and expensive to manufacture.

The Specials

At this point it would be as well to provide a few examples of some of the more "special" mortar types that are now in use. These "specials" fall into no other particular category and most have been developed for specific applications.

It has already been mentioned that light mortars have an important application in the illumination of targets for other weapons to engage, and particularly anti-armour weapons. One manufacturer, AB Bofors of Sweden, has produced a special 71 mm mortar known as Lyran that fires illumination rounds only. Lyran makes extensive use of plastic-based materials and is so designed that the ammunition carrier can act as the barrel base plate. As an alternative, Lyran can be mounted on an armoured vehicle.

Another special mortar is the Italian MISAR Raider, a minelaying system. The Raider is little more than a mortar barrel with a simple base plate plus a monopod elevating arm, all designed to launch up to 30 SB-33 scatterable anti-personnel land mines in a single firing. Each mine has a diameter of 88 mm and is fired to a range of 60 metres or more.

Then there is the so-called Salvo mortar. Perhaps more of a concept than a "special", the Austrian Noricum SM-4 120 mm Salvo Mortar consists of four 120 mm barrels mounted side-by-side and fired either in sequence or in salvo. All four barrels are carried on a wheeled vehicle such as a modified truck, or a tracked vehicle such as an M113 armoured personnel carrier. The idea is that the Salvo system could replaced artillery weapons, such as 105 mm howitzers, by combining firepower and mobility. The concept has attracted a great deal of attention but to date no orders are known to have been placed.

The Swiss 12 cm Festungsminenwerfer 59/83 is another weapon that can only be placed in the "special" class. At one time mortars were widely used in major fortifications, but now the Swiss fortress mortar is the only one left. It is actually two mortars mounted side-by-side, both loaded by automatic breech-loading mechanism that provide a high rate of fire. The weapons are located in underground chambers with only the muzzles exposed above ground. The intention is that many of Switzerland's existing fortifications, with their vulnerable frontal-facing weapon embrasures, will be replaced by 120 mm fortress mortar installations that offer a high rate of fire, reduced personnel requirements and improved protection overall.

Limitations

By its very nature the mortar is an area weapon. No matter how exactly a mortar projectile can be made to fit the interior of a barrel, and no matter how precisely fire-control orders can be formulated and transmitted, from the moment a mortar projectile leaves the muzzle, there are no end of variables affecting the trajectory over which the crew can have no influence whatsoever. Wind currents, atmospheric pressure variations, the ambient temperature, plus many other factors can all have an influence on the high angle, and relatively time-consuming, ballistic trajectory of every mortar bomb fired. These unwanted variations can only increase as the range increases. Thus the mortar can only deliver its projectiles into a general area and not against point targets.

Since most mortar projectiles have either high explosive or smoke fillings that spread their fragmentation or screening payload over an area, it can be argued that precise accuracy is not a requirement. Even so, the modern mortar is a far more accurate projectile delivery system than the mortar designs of a few decades ago.

The projectile time-of-flight factor has already been mentioned briefly. Compared to field artillery, the time-of-flight of a mortar projectile is apt to be considerable. Even at moderate medium mortar ranges, it can take a projectile 25 seconds or more to reach a target, a time period in which personnel targets can go to ground or vehicles can move to new positions or cover. This time-of-flight drawback can be overcome by combinations of good fire-control and a high rate of fire, but once fire has been opened the all-important surprise factor can be lost.

Fire-Control

At one time all mortar fire-control was carried out using a combination of range tables, slide rules and plotting boards. While accurate, such systems could be time-consuming and today they are used only as reserve or fall-back systems by many nations. The old methods have been replaced by the electronic calculator or computer.

Mortar fire-control electronics can be compressed into hand-held units that can rapidly carry out any fire-control calculation likely to be required. There are several hand-held mortar fire-control units available and their use is now widespread. All are contained within rugged cases and are powered by internal batteries.

Two of the earliest units on the market were the British Zengrange Morzen and the Marconi MORCOS. Both are currently in widespread use, the Morzen having gained the accolade of acceptance by the British Army. These two units have been joined by the Chinese AMC 11 and the French FPC 2000 (Thomson Simsa), CADET (Secre) and the CASCEN (Electronique Serge Dassault). Italy has produced the CMB-8, while the New Zealand Army uses the indigenous MERE. The Spanish Army uses a device known as Seimor, while the US Army has a small ballistic computer known as the M23. Other hand-held fire-control computers are known to be under development.

Ammunition

As with many other weapon systems, the mortar is merely the launcher. The weapon is the projectile. Recent years have seen many developments involving mortar ammunition, covering aspects from weight reduction to laser control.

Guided projectiles for use with the mortar are now possible. As yet none are in production, for the technology involved is expensive, to the extent that other weapon systems are thought by many to be more cost-effective in end-result terms. This reasoning has, in the past, brought about the demise of guided mortar projectiles such as the American GAMP, the West German laser-guided Bussard and several others. All were devised to provide the mortar with some form of anti-armour capability, with guidance provided either by laser designators or by first-generation autonomous target-seeking devices.

The development of guided anti-tank mortar projectiles continues, however (see ARMADA 2/90, pages 30 and 32). In Sweden under government contract, FFV has developed its Strix IR homing projectile to a considerable degree and many test firings have been achieved to date. The Strix projectile uses an autonomous infrared target-seeking system which directs it onto the top armour of a tank or other similar vehicle. Strix is fired from unmodified 120 mm mortars, and is handled and fired in exactly the same way as other projectiles. Maximum range is about 8000 metres.

Also intended for the top attack of armour is the British Aerospace private-venture Merlin. Developed initially for the Royal Ordinance 81 mm L16 mortar, Merlin uses a millimetric-wave radar seeker in the nose for terminal guidance. It is a long projectile, so long that it occupies most of the barrel when fired. Its maximum range of about 4000 metres is inevitably less than the 5650 metres of conventional rounds. It is expected that the Merlin terminal guidance system will eventually be applied to 120 mm mortar projectiles.

Development of Strix is being carried out primarily for the Swedish Army, but both Strix and Merlin are also aimed at a large potential US requirement. South Africa is known to be developing a terminally-guided 120 mm projectile that dispenses sub-munitions. This project is understood to involve several guidance systems, but the final form has yet to be selected.

Apart from this an European consortium consisting of British Aerospace, Thomson Brandt Armements, BPD and MFA is working on the marketing of the 120 Griffin, a 120 mm terminally guided anti-tank mortar bomb, fitted with a millimeter-wave homing head. It is due to go into production in 1994.

Away from guidance systems, several attempts have been made during recent years to improve the maximum ranges of all three classes of mortar ammunition. Some improvements have been produced by the careful streamlining of projectile bodies, but more significant improvements have been introduced by the use of flexible gas sealing rings on the projectiles. Very basically, by fitting ducing a flexible plastic or nylon sealing ring to a projectile at its widest point, it is possible for propellant gases to force the sealing ring outwards to create a sealing "skirt" that prevents the propellant gas from escaping past the projectile body while it is still travelling up the barrel. The sealing reduces "windage" and improves the maximum range and accuracy. Flexible sealing rings are now in widespread use and have been one of the major factors in improving overall mortar performance in recent years.

More dramatic range improvements can be achieved by the use of rockets that cut in at some point along the mortar projectile's trajectory. Typical examples are: * the French Thomson Brandt 120 mm PEPA (Projectile Explosif a Propulsion Additionnelle). Normally a bomb of its size and weight would have a maximum range of 4 250 metres. By introducing the rocket component, this can be increased to 6 550 metres. However, owing to its cost, the use of rocket assistance with mortar projectiles is not widespread. * the self-propelled rifled PRPA 120 mm bomb, with ranges up to 13 km; and * the long-range (17 km) TLP bomb.

The last two projectiles, fired from the Thomson Brandt 120 mm rifled mortar, are in service in the French Force d'Action Rapide (FAR).

Mortar fuzes are another area of development. Proximity fuzes for mortar ammunition are now in service but they are expensive. Far more significant are the numbers of electronic multi-purpose fuzes. Multi-purpose fuzes have been in service with conventional artillery for some time but they have been introduced to the mortar only in recent years.

A typical multi-purpose fuze can involve time, impact or graze functions. The prime function can be selected before firing but if the selected function fails for any reason, another function will take over. Thus if an impact selection is made but does not work, the time function will take over to ensure the bomb detonates. Typically, these fuzes power their electronics via nose-mounted, wind-driven generators. One example is the Israeli Alpha M787 which has two options, proximity or impact: if the proximity function fails, the point impact will still detonate the payload.

One odd little development has come from South Africa where a 60 mm red phosphorous incendiary bomb was required for bush warfare. Ideally such a projectile would use a proximity fuze to break up the projectile in flight and scatter its contents before it hit the ground. However, such a fuze would be costly and smaller than anything produced to date, so an alternative system was devised. With this system the 60 mm projectile lands and, as usual, buries itself in the ground. The tail section is then blown off and the red phosphorous container is driven backwards and upwards by a small internal charge. After a time pre-determined by a pyrotechnic chain, the red phosphorous container is blown open to spread its contents.

In order to reduce projectile weight, aluminium or other light alloys are now used for many components, including the body. The British Royal 51 mm Light Mortar fires aluminium alloy-bodied bombs.

National Tendencies

One of the main problems when dealing with mortars is that the basic mortar is a simple structure with only a minimum of components. When this is added to the fact that virtually any nation with even a rudimentary light engineering infrastructure can (and quite often does) produce mortars of all three classes - light, medium and heavy - it is evident that only highlights can be mentioned here.

Today, mortars are produced in the following countries, including Argentina, Austria, Belgium, Brazil, Chile, China, Czechoslovakia, Egypt, Finland, France, Greece, India, Israel, Italy, Japan, North and South Korea, Pakistan, the Philippines, Portugal, Singapore, South Africa, Spain, Sweden, Switzerland, Taiwan, Turkey, USSR, United Kingdom, USA, Vietnam and Yugoslavia. No doubt others can be added.

Out of this list, France used to be the nation that virtually dominated the international market, with its Thomson-Brandt mortars. Many nations continue to use Thomson-Brandt mortars and ammunition, but in recent years other nations have managed to gain large orders in the face of French competition.

One recent large order went to the United Kingdom when the US Army finally decided after years of trials and indecision to purchase the Royal Ordnance 81 mm L16 mortar to replace its ageing M29 series. The L16 is now in US service as the M252. However, that is not the only mortar import that the Americans have made recently.

In March 1990, following a five-year selection process, the US Army decided to purchase the Israeli SOLTAM 120 mm K-6 mortar to replace the old 107 mm/4.2-inch rifled mortar, in service since before WW2. Orders for over 2 000 units could result from this selection, with production eventually taking place at Watervliet Arsenal in the USA. The towed version will be known as the M285, while a version for mounting in the M113 APC will be fitted on a TT-6 carrier turntable. The M285 has a range of 7 200 metres, weighs 321 kg on its carriage and 144 kg in action. It will have a four-man crew.

The Israel armed forces greatly value the mortar and SOLTAM provides for them the whole range of mortar types, including the self-propelled 160 mm M-66, which has to be carried on an old Sherman tank chassis. The sale of the K-6/M285 to the United States will probably mean orders from other customers.

Some mortar-producing nations seem to make few attempts to sell their wares outside their national boundaries. One such nation seems to be Chile where the Army-run FAMAE concern produces 60, 81 and 120 mm mortars that are little known outside Chile itself. In contrast, Singapore promotes its mortars all over the world and has recently developed a new 60 mm Commando mortar weighing only 6 kg complete.

Spain is another nation that has had little export success of late. Once upon a time mortars from companies such as ECIA were world leaders, but of late they have not been seen outside Spain itself. ECIA mortars still look good even though they continue to use a tripod mounting arrangement in place of the more usual bipod.

Perhaps the most widelysold mortar of recent years has been the Royal Ordnance 81 mm L16 which was battle-proved in the Falklands during 1982. Apart from the large order from the US Army, the L16 has been sold to nations as diverse as Austria and Malawi. The little 51 mm L9 Light Mortar, also produced by Royal Ordnance, has not been so successful, a fact no doubt partially explained by its prolonged development period (well over 10 years).

Including all calibres Thomson Brandt claims that it has produced 30 000 mortars and 17 million projectiles. At the present day Thomson Brandt mortars equip 74 armed forces worldwide.

One nation that is still an enigma as far as mortars are concerned is China. Until a few years ago, the Chinese continued to manufacture local copies of Soviet designs, such as the 82 mm Type 53 or the 60 mm Type 31, the latter being a Soviet copy of a 1930s Thomson-Brandt design. One recent innovation, however, demonstrates that the Chinese are now entering the export market in a big way.

The innovation is the 60 mm Long Range Mortar Type W89. Other similar long-barrelled 60 mm mortars have been produced, but the Type W89 has a maximum range of 5 500 m using a special projectile, a range greater than that of any similar mortar. The high explosive projectile weighs 2.3 kg.

The USSR has made only one significant mortar innovation in recent years, otherwise preferring to retain mortar designs that date back to pre-1945. The innovation is the 82 mm Vasilek automatic mortar which is normally carried or towed by a GAZ-66 truck, the combination being known as the 2B9. The Vasilek is seemingly used more as a form of infantry support gun rather than a mortar, and is often fired at low angles of elevation over direct sights. It even has a split trail carriage and a firing pedestal. The rate of fire is reported to be 40 to 60 rounds a minute.

PHOTO : Loading a Merlin 81 mm self-homing projectile: this programme is now in its final development stages.

PHOTO : The standard 60 mm mortar produced by Armscor of South Africa. It is based on a Thomson Brandt design.

PHOTO : The Royal Ordnance 51 mm Light Mortar has a total weight of 3.05 kg including baseplate.

PHOTO : The new 60 mm Commando mortar from Chartered Industries of Singapore. The complete unit weights six kilogrammes.

PHOTO : Thomson Brandt's CL 81 breech-loading 81 mm mortar, seen here mounted on an AMX-10 TMC-81 fire-support vehicle.

PHOTO : The 120 mm breech-loading mortar from Royal Ordnance, seen here mounted on a M113 armoured personnel carrier. It fires standard mortar rounds.

PHOTO : MISAR's Raider, a special Italian mortar that fires scatterable anti-personnel mines.

PHOTO : The Swedish Bofors Lyran 71 mm mortar is designed to fire illumination rounds only.

PHOTO : The Thomson Brandt 120 mm MO-120-RT-61 rifled 120 mm mortar, a weapon frequently used as a light artillery piece by several nations.

PHOTO : The British Zengrange Morzen mortar fire-control computer is now in widespread use.

PHOTO : The South African Ratel 81, an 81 mm mortar carrier carrying a mortar of Thomson Brandt design and up to 180 projectiles.

PHOTO : The Austrian Noricum SM-4 120 mm Salvo Mortar mounted on a Unimog truck. Canadian Forces Europe have received a version mounted on an M113 vehicle.

PHOTO : Teamed with Martin Marietta and IMI, Soltam of Israel has won a $ 17 million order for 2 000 120 mm mortars.
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Author:O'Malley, T.J.
Publication:Armada International
Date:Jun 1, 1990
Words:4408
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