Infantry Guns and Heavy Mortars
An earlier version of this article appeared in G2mil
I came across an article on assault guns in Milparade. Although the author uses the term assault gun and has pictures of self-propelled systems, what he talks about mainly is a short-range large-caliber towed system.
History of artillery clearly demonstrates that creating a large-caliber but light enough system is quite realistic. As far back as in prewar years, the 152mm Rheinmetall-developed mortar, model 1931, weighing 1,150 kg and having a firing range of 5,000 m was adopted for service with rifle regiments in accordance with a new system of artillery armament (1933 - 1937) approved by the Soviet Revolutionary Military Council on August 5, 1933. Unfortunately, unreasonable solutions led to the removal of the mortar from the inventory. At the same time the German counterpart showed to advantage during the war.
Today, advanced level of artillery science and technology makes fairly realistic the development of a 152mm towed assault gun weighing less than 900 kg and having a firing range of up to 5 km. Reduction of the gun weight can be achieved through the use of new powders providing an optimal burning law, barrels made of high-strength crack-proof steels, including martensite steels, gun carriages made of titanium and aluminum alloys, reduced weight projectiles, and other design and technological measures.
It took me a moment to realize what this weapon would be in western terminology. What is described very closely resembles the larger varieties of infantry gun, even though the author at no time states this weapon would be under infantry control. To avoid confusion for the rest of this article I'll refer to the weapon as a heavy infantry gun rather than as an assault Gun, since the latter has a different meaning in English.
Infantry gun may bring to mind an image of small direct fire weapons but in fact German Army regiments also had a battery of larger 150mm infantry guns that were used for both direct and indirect fire. These are probably the weapons described as showed to advantage.
The sIG33 15cm infantry gun had a range of 4,700m and fired a 29kg (63lb) shell at 240m/s. Between two and six weapons were held by each infantry regiment in an infantry gun company.
The role of the proposed weapon system overlaps a little with that of the proposed 155mm mortars.
The Russians already deploy 160mm mortars and the Russian author quoted above sees no confliction of roles.
Self Propelled 155mm Heavy Mortar.
To understand the role of the heavy infantry gun it is necessary to understand some of the features of heavy (152-160mm) mortars.
While the Russian M-160 is a breech-loading weapon the Finnish M-58 and the Israeli M-66 that is based on the Finnish design are muzzle loading.
The Finnish and Israeli weapons have the barrel supported by a central column that is designed so the muzzle can easily be lowered for loading. In practice loading a 40kg bomb by the muzzle is just as quick as breech-loading yet is mechanically simpler. Czechoslovakia built a pair of prototype 152mm mortars, but I've no information on whether the shells used were the same as the 152mm field guns.
Because of their weight and the tendency of the base-plate to take root large mortars are best used in a self-propelled form, fired from a truck bed or the floor of an APC. The Israelis found that the 160mm weapons they captured and later produced themselves were most effective this way, the usual vehicle being a Sherman tank hull.
A good vehicle for carrying a large calibre mortar would be a variant of the M113, which is already used to carry 120mm mortars. Retractable recoil spades may be necessary to reduce stress from firing to the suspension and it would not be possible (or desirable) to dismount the weapon. Since the weapon is breech-loaded the fighting compartment could be protected by a roof or very low turret.
Such a SP 155mm mortar vehicle could be a very light weapon system (relatively speaking) with most of the vehicle's weight being from the ammo load. The SP 155mm mortar carrier is therefore capable of going nearly anywhere and killing nearly anything. The 155mm SP mortar carrier would be a good support vehicle for Maneuver elements or forces engaged in Urban combat. It's relatively modest range would be offset by its ability to keep up with the main force, the wider choice of firing locations it could select and its ability to Shoot and Scoot. The SP 155mm mortar would be a useful compliment to vehicles carrying light or medium Multiple rocket systems. The MBRLs could provide saturation fire while the mortars could provide more sustained fire. Use of such systems with Maneuver elements would also free up heavier longer ranged artillery systems for more suitable missions.
It should be possible to design the mortar vehicle so that is can be easily carried by a heavy-lift helicopter. Used in such a way such a vehicle can provide an indirect fire capability to units that are otherwise entirely mounted on helicopters. This may allow ADA to be suppressed without exposing aircraft to fire.
155mm mortars should prove to be lighter than howitzers and easier to manufacture. An interim design of 155mm mortar could possibly be created by fitting 160mm smoothbore weapons with new barrels or rifled inserts.Since it is the same calibre as a 155mm howitzer the 155mm mortar can use rounds developed for the former weapon such as the M483 DPICM warhead, M449 anti-personnel bomblet warhead or M898 SADAM.
The Russians and the armies they influenced seem to have used the 160mm mortar in a heavy mortar battalion that was part of the Divisional Artillery. They seem to have been particularly popular with mountain divisions due to their range, high explosive content and high angle of fire. They are also noted as being useful for the destruction of point targets in urban settings.
The heavy infantry gun differs from the heavy mortar in that it can be towed by a light vehicle or more easily heli-lifted into position. It is therefore more suitable for supporting units in mountainous terrain or light airborne or airmobile forces. Also, unlike the heavy mortars, the heavy infantry gun can be used in a direct fire role. The gun carriage should be based on designs such as the M119, Italian 105mm pack howitzer or Russian D-30. The Italian weapon has the interesting feature of not only being man-packable but capable of being assembled in a low configuration for direct fire roles.
It is likely that both a 155mm infantry gun and 155mm Heavy mortar will use the same propellant charges as well as the same projectiles.
An idea that will obviously occur to the reader is the possibility of having a self-propelled version of an infantry gun that can provide direct-fire and serve as a true Assault gun.
The weapon's recoil mechanism and traversing and elevation gear would probably take up too much space in an APC-sized vehicle. Vehicles that have mounted similar weapons in the past have either been too heavy to be moved by helicopter or would lack sufficient armour to be used in a direct-fire role if they were of helicopter liftable weight. Ammo capacity of a 155mm armed APC sized vehicle would also probably be too low for a direct-fire vehicle.
With a 155mm heavy infantry gun fitted a medium tank might serve as what Mike Sparks terms a Modern Siege Engine, although systems such as the 120mm assault gun-mortar may prove more useful if something lighter than a MBT is needed.
A useful support gun could be made from a 120mm gun-mortar mounted on a field carriage. Since this uses the same ammunition as muzzle-loading mortars a couple could be placed in the mortar platoon of infantry battalion using convention muzzle loading mortars without complicating logistics. Carriage-mounted gun-mortars could be used by the battalion commander as a direct fire weapon to defend fixed positions or as an indirect fire support weapon. Such a weapon should have a shield, low silhouette and be capable of being man-packed if necessary. The 120mm weapons might replace the 105mm light gun in Light formations.
As it turns out, the Russians have already built a similar 120mm weapon:-
All the Nona-series weapons are rifled and designed to use a spin-stabilized round with a range of up to 8,800m for conventional rounds and 13,000m for rocket assisted. Cargo and Guided rounds are available. As well as Russian-made ammunition they can also fire French TBA rifled rounds (the French rifled mortar is in service with 22 countries). The Nonas can also fire most finned rounds intended for conventional smoothbore 120mm mortars such as the 2S12.
The Nona-M resembles a 120mm version of the Russian M-160 and has a similar performance to the French 120mm Rifled mortar. Whilst the French 120mm weapon weights ca 500kg and can only be fired from positions accessible to the towing vehicle the Nona-M weighs 390kg and can be broken down to four smaller loads of not more than 100kg. This weapon has considerable potential for use in mountainous terrain where the near vertical descent of the round will be particularly effective and the use of vehicle mounted systems may not be possible. I'm not sure if the Nona-M can be used for direct fire or if it got past the prototype stage.
The Nona-K is mounted on a gun carriage, weighs 1,200kg and is also capable of direct-fire.
It is possible that both of these weapons were developed in response to the Milparade article quoted above since they seem to meet many of the needs described. Russian sources claim that the 120mm mortar bombs have a destructive potential on par with 152mm/155mm Artillery shells so maybe there is no need for a 155mm infantry gun or heavy mortar. Certainly it simplifies logistics if weapons can also use the ammo for an infantry battalion's muzzle-loading weapons.
The Nona-series also includes several vehicle mounted versions, some of which have been adopted by Russian Airborne and Naval Infantry forces. These use the same ammunition as the Nona-M and –K.
The West has several models of vehicle-mounted 120mm gun-mortar that could be mounted on a carriage mount. A mounting resembling that used with the Italian Pack Howitzer would probably serve for both the Nona-M and Nona-K roles. An interesting capability of the Italian weapon is that it could be transported concealed in a M113.
The full potential of modern 120mm Mortar systems has yet to be fully exploited. As well as seeing these weapons as part of an infantry or armoured battalion we may see mortar battalions fielded as part of a division, brigade or strike group. World War II CW Battalions were mainly used to lay smoke and explosive fires and had 36 4.2 mortars. One company of 12 weapons was believed to be equal to a battalion of 105mm Howitzers.
The 120mm mortar is an even more capable weapon than the 4.2. While I can see the majority of the battalion armed with muzzle-loading M120s there sould be at least a platoon of self-propelled automatic systems such as Vena or AMOS. These can be used for saturation fire or long-range delivery of guided rounds. Such a battalion might also have a couple of platoons of 155mm or 160mm mortars.
It is in fact likely that larger mortar systems such as carriage-mounted 120mm gun-mortars or heavy infantry guns become the responsibility of the Artillery in modern armies.
Smaller Infantry Guns
Since at least the 18th century many armies have given their infantry regiments light artillery that were under their own control. While Commonwealth and US forces showed little interest in infantry guns the majority of World War Two combatants did use some form of infantry gun.
Most infantry guns used by armies were smaller than the German 150mm. Infantry guns have tended to be compact and light to give them the handiness and mobility required for infantry use. Since weapons were mainly used for direct fire long range was not a major requirement.
As well as the 150mm sIG 33 the Germans also used a 400kg 75mm weapon. These were held in the regimental infantry gun company but were often deployed in a two to four gun platoon at battalion level. The 75mm infantry gun could project a 6kg shell to 3,375m. It could be easily man-handled into position or broken into man-portable loads.
The Japanese equivalent weapon, the 70mm Type 92 battalion gun (below) only weighed 212kg but had a range of nearly 3,000yds. It could drop indirect fire rounds as close as 100yds from its position. Where most WW2 infantry battalions had a platoon of medium mortars a Japanese infantry battalion instead had a platoon with two to four infantry guns. 75mm Type 41 guns were also held in a company at regiment level.
Some armies also provided explosive shells for their anti-tank guns so that they could be used in an infantry support role. The Russian 45mm ATG was classed as a regimental gun and expected to serve a dual role. However, as anti-tank guns grew in size they became less manoeuvrable and therefore less suited for offensive operations. The Japanese redesignated obsolete 37mm ATGs as infantry guns and moved them to infantry gun platoons.
Some US Army infantry regiments had an infantry cannon company. These didn't use a true infantry gun and instead used the 105mm M3 Howitzer which weighed 1.2 tons.
One idle afternoon I had been considering what weapons would be suitable for arming a river patrol boat, and it occurred to me that a 1930's infantry gun (left) would be ideal.
Is there a modern equivalent to the compact infantry gun? An 81mm gun-mortar might fit the bill, and actually these have been demonstrated fitted to light boats. Following this train of thought it occurred to me that a light infantry gun might still be useful for defending positions such as roadblocks or small garrison posts. It is actually a little surprising that a gun-mortar mounted on a light carriage hasn't been offered by manufactures.
There still seems to be a requirement for direct fire weapons that are more powerful or longer ranged than RPGs, even for convert urban operations as described here.
During the Battle for Berlin towed guns were sometimes found to be more useful for direct fire than tanks or assault guns.
The infantry gun offers long range direct fire from positions that would be inaccessable to a vehicle-mounted system. Compared to a recoilless gun an infantry gun makes more effective use of propellant which offers more compact, lighter rounds so more can be carried by the firing unit. Since the weapon has no backblast the crew have greater flexibility in chosing a firing positioning and concealment. For example, in a counter-guerilla scenario an infantry gun could be positioned on a street without concerns that backblast will injure civilians or damage property. A small infantry gun could actually be fired from the interior of a building or bunker or from the rear door of a van or APC. The infantry gun has a greater direct fire range than most shoulder fired man-portable anti-tank systems, allowing a firing position out of small arms range when terrain allows. Most guns also offer armoured protection for crew although such protection can be added to other systems such as recoilless guns. This page shows a wheeled shield for a Russian Bazooka/Panzerschreck-type weapon, the SPG-82.
Many infantry guns were mountain guns. The M8/M1A1 75mm Pack howitzer was extensively used by airborne, jungle and mountain forces during World War II since it could be taken places were other field guns could not, and since the Americans and British had no infantry guns, it was forced into a direct fire role too. This weapon weighed a shade over 600kg, but could fire a 14lb shell to 8,700m. A 98mm gun-mortar on a suitable carriage (a pack morwitzer) would create a useful replacement for the various aging 75 - 105mm weapons used by mountain units.
Maj. Roy Farran of 2nd SAS found his single pack howitzer invaluable during his mission supporting Italian partizans. Ridgetop roads offered little cover for conventional ambushes so the pack howitzer was used to fire on traffic from a distance. While a cart-mounted muzzle-loading 120mm mortar may have a similar performance in an indirect fire role such a weapon has a minimum range of 200m and is not as suitable for engaging moving targets.
The Russian 76-27, also know as the 76 RK/27 or 76.2mm Obr. 1927 had a similar performance to the M8 but was issued as an infantry gun. It weighed 780kg and could fire a 14lb shell to 8,850m. It was also widely used by German units as the IKH-290 (r), more than 1,800 being in German service.
My initial thoughts were that there might be many modern applications for something like an 81mm or 98mm gun-mortar mounted on a light carriage, possibly with a co-axial machine gun and a ranging laser. Such a mounting would need a shield for crew protection and be man-packable if necessary.
At the end of WW II, a very light type of gun carriage was developed by the Germans for the PAK 41. Instead of the gun-shield being an afterthought it was the main foundation of the carriage, onto which the trail legs and wheels were attached, and the gun mounted in the middle by a gimbal joint. It's possible that such a mount may lack sufficient elevation for the infantry gun role.
The PAK 41 type carriage could also mount a 90mm M67 or 106mm M40 recoilless rifle. It is possible in such a configuration would allow the rounds could be fired from a closed breech as was done for the 73mm SPG-9 recoilless Gun round when it is used in the turret armament of the BMP-1. The German Raketenwerfer 43 Püppchen used a similar system.
The Püppchen fired standard 88mm Panzerschreck rockets from a conventional barrel mounted on a low silhouette carriage, increasing range from around 165m to 700m. If this can be done it will allow greater flexibility in positioning the weapon and may yield improvements in performance.
No discussion of carriage-mounted weapons firing mortar bombs would be complete with mentioning the Wartime German PAW 600, also known as the PWK 8H63. This used a round that was comprised of an 81mm mortar bomb, a casing from the LeFH-18 105mm Howitzer and a perforated steel plate with a spigot. The mortar bomb was fitted to the spigot with a shear pin and the propellant charge was 360gm diglycol. The PAW 600 was one of the first weapons to use the High-Low pressure system now familiar from 40mm Grenade Launchers. This allowed a powerful charge to be used with a light barrel. The entire weapon weighed only 600kg but had a muzzle velocity of 520m/s (1,706 fps) with a 6lb HEAT shell. This compares very favourably with the 1,260 fps muzzle velocity of the L24 75mm gun used by the Germans as a vehicle-mounted close-support weapon. In the anti-tank role the PAW 600's HEAT round could penetrate 140mm of armour at 750m, while for indirect fire range is given as 6,000m. The same bomb fired from the GrW34 mortar only reached 2,400m. While intended as an anti-tank weapon there can be little doubt that the PAW 600 would also be used as an infantry support gun.
With modern mortar rounds such performance might be easily exceeded. A modern version of the PAW 600 could either fire conventional rounds, like current gun-mortars or the bombs could be pinned onto cartridge cases for high velocity shooting.
The only 81mm gun-mortar design I can find information is the Thomson-Brandt Armament's (TBA) which is intended as vehicle armament and described as weighing 500kg. To this weight must be added a carriage and shield and this is obviously far too heavy. The Russians have a carriage-mounted version of the 82mm Vasilyek automatic mortar. The Chinese version is the W99. These weapons weigh 630 - 650kg without a shield although weight could be reduced if the automatic fire mechanism is deleted. The PAW 600 weighed 600kg but this weight could probably be reduced using modern materials and by possibly designing the weapon for standard velocity mortar bombs only. I do however have my doubts that the weight of a 81mm weapon can be made any lower than 400kg. A 98mm weapon of similar weight to the M8 75mm pack howitzer may be acceptable.
Modern thoughts on infantry tactics differ somewhat from 1930's ideas that were based around large infantry divisions. If modern weapons are not truely man-portable they are usually vehicle-mounted. Recoilless guns are lighter than infantry guns and offer a more potent anti-tank potential.
The modern infantry gun is NOT an anti-tank gun and one of the biggest obstacles to using these weapons is that many officers will be unable to grasp this fact. An infantry support gun is no more an anti-tank weapon than a machine gun or mortar is.
An APFSDS round is offered for the TBA 81mm gun-mortar but penetration is a not very impressive 90mm. The velocity of 1,000m/s does suggest some interesting ideas for using the round against soft-targets. A HEAT round is available for the TBA 60mm gun-mortar with 200mm of penetration. Based on the performance of recoilless weapon rounds of similar calibre a 81mm HEAT round should offer between 250-400mm penetration. Such a round would, however mainly be used against field fortifications and light vehicles. While man-portable weapons with this performance can be used effectively against the flanks or rear of a tank the infantry gun will not have the mobility to use such tactics. If it is used against tanks it is likely to have to make shots against their frontal armour. This problem can be answered by using the infantry gun for its intended role and deploying anti-tank systems with it where needed. By firing against infantry and APCs a correctly used infantry gun can facilitate the mission of anti-tank teams.
There may be a good case to rename the infantry gun to stress that it is not an anti-tank weapon. Various other names have been used for infantry guns, including infantry howitzer or infantry support howitzer. Since the weapon we are considering will probably fire mortar ammunition infantry morwitzer may be a better term.
Since a 81mm Morwitzer is likely to be too heavy this prompts the question as to whether a smaller calibre could be used and still result in a useful weapon. TBA's 60mm gun-mortar weighs around 75kg so if fitted with a gunshield and mounted on a carriage we will probably have a weapon of similar weight to the Japanese Type 92 battalion gun. At 212 kg such a light weapon could be physically carried over rough terrain when needed. Although the Japanese battalion gun nominally had a crew of five each gun was assigned an NCO, two spotters and 12 gunners so there was plenty of muscle to carry ammo or the weapon itself if needed.
The TBA 60mm LR gun-mortar has a range of 4,000m, a 1.8m barrel and a muzzle velocity of 250m/s. The mounting for the weapon would most likely be based on Type 92, being capable of adopting a high configuration to give breech clearance when firing at a high angle and a low silhouette for direct fire. A compact battery-powered auxillary propulsion unit might prove useful in moving the weapon under combat conditions.
In modern usage 60mm morwitzers are likely to be assigned to infantry companies on a as needed basis so 60mm calibre allows the weapon to utilize ammo already supplied for the unit's company and/or platoon mortars. The most likely organization I can see for a pair of morwitzers to be held by the battalion HQ with a skeleton crew. Two men per gun and a corporal in charge is probably about right and when morwitzers are not deployed these men can fullfil various duties around BHQ. Personnel from the infantry company the morwitzer are assigned to can be attached to the weapons should a larger crew be needed.
Ceremony is important to military units and morwitzers could also be used as saluting guns for parades etc.
As well as military applications the light morwitzer may also prove to be a useful item for police SWAT units. Such a small weapon could easily be carried in the back of a police van and could use a range of non-lethal rounds in addition to military loads. The 56mm grenades developed for the Alsetex Cougar launcher would appear to be a good basis for such rounds. As well as riot-control ammo the morwitzer could also fire non-explosive kinetic energy rounds for opening doors from a distance.