Artillery Mortars

[sillygoose]

Inspired by this design:
Finnish Tampella 160 mm mortar system and extended-range HEFSDS projectile - Armament Research Services (ARES)
Microsoft Word - 129 Makkonen, A.doc (maanpuolustus.net)

Before WW2 mortars were mostly developed for infantry battalion or regimental use and were generally no greater in size than 105-107mm with the exception of the French Brandt 120mm mortar. They had two designs, one an artillery mortar and one infantry mortar with the former intended for divisional artillery usage and the latter for regimental fire support. This went on to inspire the Finnish and Swedish 120mm mortars and through them the Soviet ones, which in turn inspired the German one, etc. The artillery version was basically ignored and the only heavy mortars (not counting the super heavies) fielded by the end of the war were the Soviet 160mm breach loaded mortar and 210mm German/Skoda one that was fielded at the very end. Post war there were a bunch of developments, including the Finnish ones detailed in the link above of 160mm and 300mm as well as the (in)famous Soviet 240mm Tulpan mortar.

What if though more development and investment in heavy mortars happened in the inter war period? It seems in the context of large armies fighting a world war mortars would be a cheap artillery replacement with the right development such as the extended range shells the Finnish developed. Both the high aerodynamic 'regular' mortar shells and the discarding sabot 'spike' shells, with a 16km range and 530m/s muzzle velocity. That actually outperforms a number of 105mm howitzers though with a resulting explosive content quite a bit lighter. Still the weapon itself even with more expensive sabot shells was lighter and cheaper than a howitzer. However even the 'regular' aerodynamic shells of 160mm diameter could reach a muzzle velocity of over 400m/s (nearly double that of a standard mortar shell) and reach over 10km. Accuracy was said to be good even at fully range and that muzzle velocity it is quite impressive for a heavy caliber mortar. The above version is an Israeli version of the mortar with 'only' 9.6km range. I'm guessing that is the more likely range in combat conditions. The weight was less than that of the lightest artillery 105mm howitzer I can find from the period and is probably considerably cheaper to make and operate. The shells would also be double the weight of a 105mm howitzer for a 160mm version, though I'd imagine for countries with 150-155mm howitzers they'd try to field something in that caliber instead with somewhat lighter munitions; so it wouldn't be a 150mm howitzer replacement, just something filling the gap between the 105 and 150-55mm guns in terms of throwing weight.

Additionally since there was already research into smooth bore 'arrow' shells that would be viable with WW2 tech:
Peenemunde Arrow Shell - Nevington War Museum
A 150-160mm mortar could use a 105mm arrow type sabot shell to reach at least 12km, which would have more explosive content than a 120mm shell if not more. I'm basing that on the above articles that claim the 80mm arrow shells had 1.5kg of explosives while a conventional 120mm shell had 2-2.5kg explosives; that is due to the length of the shell which makes up for thin width.

What does the community here think, were heavy mortars a worthwhile 'add' to infantry divisions as additional fire support assets? Especially with extended range munitions, perhaps instead of using/developing infantry guns. I'm thinking they'd be concentrated in a battalion at the division level like the Brits did with their 4.2 inch mortars. Heavier stuff in the 210-300mm range would be in independent artillery brigades like the Soviets did with their 160mm mortars.
160mm Mortar M1943 - Wikipedia

Could they potentially even replace 105mm howitzers for certain applications especially with the arrow shells? How about self propelled versions? Modern 120mm truck mounted SP mortars exist:
China Defense Blog: Norinco SP-9 truck mounted 120mm gun/mortar system (Sino Zauralets??) in PLA color (china-defense.blogspot.com)

A 150-160mm mortar on a light tank chassis should be viable with spade support and a muzzle brake especially if a 150mm infantry gun could be mounted:

Or much heavier guns on very light chassis:

A breach loaded 160mm SP mortar with option to use an extended range shell seems to me at least to be a highly useful fire support asset especially if it can rival or exceed a 105mm SP howitzer in range and payload per shell. Maybe ideal for an armored or motorized division.

Thoughts?

 

[PsihoKekec]

While there are plenty of mounted variants of mortars, the problem is that once you get to the breech loading mortars you have similar levels of complexity as with howitzers, especially if you take into account the specialty ammunition that you need, to get comparable ranges. Thus the ''selling point'' would not be the range, but the weight of fire, so these weapons would sacrifice the range for heavier rounds, a very useful feature in urban combat - 160 mm mortars the Syrians used in Lebanon were quite feared, due to their ability to ''eat their way'' through the floors of multi story buildings.
Thus instead of expensive extended rang rounds, the development would be the heavier shells with shorter range than normal ones, but bigger effect, perhaps also penetration rounds with rocket assist in terminal phase (enemies in the cellar). Also, once the guided warheads come into fashion, due to lower muzzle velocity it will be easier to make the guidance package for mortars than it is for howitzer and with the payload of 160 mm and 240 mm mortars, it is an economicaly justifiable project to do it.

 

[sillygoose]

While there are plenty of mounted variants of mortars, the problem is that once you get to the breech loading mortars you have similar levels of complexity as with howitzers, especially if you take into account the specialty ammunition that you need, to get comparable ranges. Thus the ''selling point'' would not be the range, but the weight of fire, so these weapons would sacrifice the range for heavier rounds, a very useful feature in urban combat - 160 mm mortars the Syrians used in Lebanon were quite feared, due to their ability to ''eat their way'' through the floors of multi story buildings.
Thus instead of expensive extended rang rounds, the development would be the heavier shells with shorter range than normal ones, but bigger effect, perhaps also penetration rounds with rocket assist in terminal phase (enemies in the cellar). Also, once the guided warheads come into fashion, due to lower muzzle velocity it will be easier to make the guidance package for mortars than it is for howitzer and with the payload of 160 mm and 240 mm mortars, it is an economicaly justifiable project to do it.

Certainly the breach loading would increase complexity, but going by the PAW system which used similar ammo, it was still quite a bit cheaper and lighter than rifled barrel AT gun. So not really similar complexity especially given the lack of a recoil mechanism.

I was thinking the extended range/arrow shells would be for special occasions when needed, but the general use would be the regular rounds. Still even the streamlined 'super Tampella' shell (a standard mortar shell in terms of layout, but optimized for aerodynamics) had an impressive range of 9.6km. Not only that, but due the longer shape it also had a higher payload.

BTW do you think a ring type sabot on say a 120mm mortar shell plus full bore (say 160mm) tail fins to extend range? That should be pretty simple given how it is the basis of APFSDS ammo.

But on a shell like this with bigger fins:

Still if you were interested in exceptionally heavy shells those existed too IOTL:

https://en.wikipedia.org/wiki/21_cm_GrW_69

It fired a light bomb of 85 kilograms (187 lb) and a heavy bomb of 110 kilograms (240 lb).

21-cm-GrW 69 (21cm minomet) : Německo (DEU)

21-cm-Granatenwerfer 69 minomet 210,9 mm / 8 ¼ in DD.11.1944-DD.03.1945

www.valka.cz

A sub-caliber 170mm projectile in the 210mm mortar would be equivalent at least to a 150mm howitzer shell. Especially if long and streamlined like a V-2 missile:

 

[sillygoose]

I've given this what if a bit more thought lately on account of reading various things.
One good way to implement this is the Russian/Soviet gun-mortar system:

Army Guide

Army Guide - information about the main battle tanks, armoured vehicles and armament of the land forces and also the information concerning other army subjects - 2B16 Nona-K, Towed gun, Weapons & Weapon Systems

www.army-guide.com

But at the brigade/regimental combat team level. In WW2 it seems many countries experimented with 105mm howitzers pushed down to a regimental size combined arms group, notably the US regimental combat teams and the German experiments with the 78th Sturm Division. It seemed to work for the US, which led to the post-war brigade structure, while for the Germans it did not due to their smaller HQs. Herman Balck proposed a reformed structure for the Grossdeutschland division that regrouped it into 3 brigade combat teams with both a regimental HQ for tactical combat and the brigade HQ for managing the logistics and organizing the various non-regimental assets of the whole brigade, which would fix the issues with the German attempt at a regimental combat team. Nevertheless the issue with using 105mm howitzers pushed down to regimental support is that it is pretty overkill given the range and weight. A gun-mortar system could be a cheaper, lighter replacement that still fills the same role.

The late Soviets stumbled into a better solution with their 120mm gun-mortar system original meant as light artillery for their VDV units, but the modern Russian army realized it would be an excellent mobile fire support platform for all their brigades. Plus it also could fill the role of an infantry gun if needed due to the direct fire capabilities. It is much like the US Marine's Howtar from the 1960s, which mated the 4.2 inch mortar to the 75mm pack howitzer carriage and made it surprisingly mobile and versatile as a support platform despite the large increase in weight. Marines that used it loved it, but the brass took it away due to various modernization schemes. However during WW2 the 105mm pack howitzer carriage should be a good platform to handle a 120mm gun-mortar, same with the German 105mm mountain howitzer carriage. For the Brits the Aussie designed/made 'short' 25 pounder which was significantly lighter would provide a good carriage. The Soviets lacked an easily convertible carriage, but the M-30 122mm howitzer could be the starting point if they shaved off considerable weight.
This 120mm gun-mortar would have to have a longer barrel than WW2 120mm mortars, much like the modern 120mm Russian system it would probably be L/24.

In covering the infantry gun role it could also use HEAT ammo as well, so still have some AT utility. Not unlike the PAW 1000 system. Just with shorter range.

This could also work for the 4.2 inch/105mm or 107mm mortar systems of WW2. The Germans tried to extend the range of their 105mm mortar with hilariously overengineered result:

https://en.wikipedia.org/wiki/10_cm_Nebelwerfer_40

Had they mated that breach loaded mortar (with a longer barrel) to the 75mm mountain howitzer carriage/recoil mechanism they probably could have turned it into a more useful system. The Skoda 75 seems like a good option, though the barrel length might be an issue:

https://en.wikipedia.org/wiki/Skoda_75_mm_Model_1939

For a WW2 brigade it would have been a much cheaper and lighter option with as much if not more punch than a 105mm howitzer shell, though with shorter range. Still given the Russian system using conventional ammo has a range of 8.8km that seems plenty good for a brigade support weapon. Plus it still leaves open a role within the regiment for a lighter 120mm drop fired mortar system as well (infantry vs. artillery mortars) with shorter range, but using the same ammo.

Meanwhile it lets the division concentrate its artillery assets so they can be used to greatest effect. But with the 105mm role covered that would let divisions use heavier, longer range artillery instead, say 3 battalions of 150-155mm artillery instead of the normal structure of 1x150-55mm howitzers and 3x105mm howitzers for most armies. The 105 could be eliminated entirely much as it has been in the modern era, which allows for economies of scale for the 150-155mm systems. Arguably that also leaves room for a ~128mm artillery system for longer range roles for the division as well.