98mm Mortars.

<XMP><BODY></xmp>98mm Mortars.

Added 14-6-14
Updated 19-11-15

98mm Mortars.
The terms of the CFE (Conventional Forces Europe) Treaty restricts the individual national holdings of numbers of artillery tubes of 100 mm calibre or greater including mortars.

This has lead several countries such as Slovakia and Poland to develop and adopt 98mm mortar designs. Comparison of these weapons with examples of 81mm and 120mm weapons is informative.

	81mm M252 (US/UK)	120mm M120 (US/Israel)	98mm M98 Poland	98mm ZTS Model 1997 Slovakia
Weight	55 kg	145 kg	115-136 kg	114 kg
Range	83-5,608 m	200-7200 m	400-7000 m	300-8000 m
Rate of Fire Sustained	30 rd/min for 2 minutes. 15 rd/min indefinitely.	16 rd/min (first minute). 4 rd/min (indefinitely)	15 rd/min	12-15 rd/min
Casualty Radius	38 metres dia* (M899/821)	60 metres dia*	75m blast radius*	75m blast radius*
Bomb Weight	4.5 kg (M899/821)	13.18 kg (M57)	8-10 kg	8.4 kg

*FM23-90 descibes the “effective bursting area” of the M899/M821 81mm rounds as being of 40m diameter and states that the 120mm has a Bursting Radius 75 meters.
        Bursting radius and Effective radius are not the same things. Effective radius is generally described as the distance one would expect 50% casualties at. The issue is confused further by some performances being given as diameters rather than radiuses. 7-90 gives a 38m diameter effective area for 81mm and 60m diameter for 120mm weapons. A Polish catalogue claims a 75m blast radius of their 98mm mortar (this may be a translation error). The US M30 4.2” mortar is listed in JIW 2002-2003 as producing a 40x 20m effective area but it seems reasonable to expect more modern ammunition of similar calibre to be more effective. I suspect the 98mm rounds will give an effective area of at least 45m diameter. Having a smaller effect area than the 120mm for battalion mortars may not be too much of a disadvantage in actual practice. It may reduce collateral damage or the danger to friendly troops that the mortars are fired in support of.

        Having been designed to replace 107mm and 120mm weapons the range of the 98mm is about the same and a considerable improvement over 81mm weapons. The information I have is that 98mm HE rounds are about 8-10 kg in weight. This is about twice the weight of a single 81mm round and 50-60% the weight of a 120mm.

        This is not the whole story, however. One of the advantages the 98mm round has over the 81mm is that its greater capacity makes it more suitable for cargo rounds. At least one ammunition manufacturer is offering a 98mm round carrying multiple HEAT-Fragmentation bomblets. With such rounds not only does a single 98mm round have greater capability against light armour but it can also cover the same area as several 81mm rounds.

        While the current designs of 98mm weapon on offer are somewhat lighter than 120mm weapons they are still nowhere near the 81mm weapons in man-portability. Both the Polish and Slovak designs have handy light trailers that can serve as handcarts that a couple of men can move. The position of the 81mm in the battalion niche is however threatened by another competitor. Several companies offer long range versions of their 60mm mortars. The Denel M6 is currently replacing the 81mm mortar in South African service. The specially developed 2.2kg long range 60mm bomb is claimed to have similar destructive effects to a 81mm and a somewhat greater range (6,200m). Since many armies use 60mm mortars at platoon or company level adopting a LR 60mm weapon as a man portable battalion weapon offers numerous logistical advantages.

        Whilst current infantry battalions may use a mixture of 60mm, 81mm and/or 120mm weapons a future force could easily make do with 60mm and 98mm.

        The 98mm weapons that I have seen appear to be scaled-up versions of 81/82mm designs. What sort of weapon might one have if instead a 120mm weapon was fitted with a smaller calibre barrel? In particular I'm thinking of weapons like the French 120mm Rifled Mortars which were used by over 22 nations and often used like light howitzers. Given the weight of these weapons reducing calibre is not going to significantly reduce the weapon's weight so one might as well use the saving to create a thicker barrel capable of handling more powerful propellant charges. A slightly longer barrel may be possible too but given that the weapon is muzzle loading there are limits to how practical this will be. A thicker barrel would permit a higher sustained rate of fire. A 98mm weapon capable of firing to beyond 13km should be possible and under the CFE treaty would not be classed as artillery.

        If the 98mm weapons do gain popularity the other weapon I expect to see soon is a breech-loading design suitable for mounting on armoured vehicles. A version of this on a light carriage may have useful applications too. A 98mm “pack morwitzer” would be useful for jungle, urban and mountain operations and in the defence of positions. Canister, HESH and HEAT ammunition is likely to be developed for direct fire 98mm weapons.

Sources:
Jane's Infantry Weapons 2002-2003.

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