Infantry Guns and Heavy Mortars

      After reading the article on 155mm mortars, I came across an article on assault guns in Milparade:-(http://www.milparade.com/2000/38/03_01.shtml).

      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.

     It took me a moment to realize what this was in western terminology - an Infantry Gun. "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 the weapons "showed to advantage." www.waffen-ss.com/equipment/artillery/150-mm_heavy_infantry_gun.html

The role of the proposed weapon system overlaps a little with that of the proposed 155mm mortars. The Russians already deploy the 160mm mortar and the author sees no confliction of roles.  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.  As the weapon is breech loaded the fighting compartment can be protected by a very low cover or turret. The 155mm mortar vehicle could be a very light weapon system with most of the vehicle's weight being from the ammo load. The 155 mortar carrier is therefore capable of going nearly anywhere and killing nearly anything. 155mm mortars should prove to be lighter than howitzers and easier to manufacture.

     When carried by a heavy lift helicopter, 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.  An interim design of 155mm mortar could be created by fitting 160mm smoothbore weapons with new barrels or rifled inserts.  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. Also, unlike the heavy mortars, it 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 mortar 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 serve as a true Assault gun. Due to the space taken up by the weapon’s recoil mechanism and traversing and elevation gear, an APC sized vehicle may have insufficient armor and defensive systems or lack sufficient ammunition capacity.

There maybe ways around this. Many effective assault guns have been of a turretless configuration: http://www.achtungpanzer.com/stug.htm and http://www.achtungpanzer.com/brum.htm and http://www.inf.upol.cz/~stepanos/museum/stuig33.html 

Smaller Infantry guns 

     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 would be ideal.  Is there a modern equivalent?  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 position such as roadblocks or small garrison posts. 

    There still seems to be a requirement for direct fire weapons more powerful than RPGs, even for convert urban operations as described at:

http://call.army.mil/call/fmso/fmsopubs/issues/nightstalker/nightstalker.htm

     The M8 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. While a cart mounted 120mm mortar may have a similar performance in an indirect fire role, such a weapon has a minimum range of 200m.  There might be many modern applications for something like an 81mm 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.  An extension of this idea was a carriage mounting a 120mm Gun-mortar. This could be used 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. Such weapons might replace the 105mm light gun in Light formations.

     The PAK 41 type carriage could also mount a 90mm M67 or 106mm M40 recoilless rifle. It is possible in such a configuration the rounds could be fired from a closed breech, as is done for the 73mm SPG-9 round when it is used in the turret armament of the BMP-1. This 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 (1706 fps). In the anti-tank role its HEAT round could penetrate 140mm of armour at 750m, while for indirect fire range was given as 6000m. The same bomb fired from the GrW34 mortar only reached 2400m.

     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.

     
Phil West     phil.west@angelfire.com