Alternative light and anti-tank guns, 1935-45

Shortround6 said:

Not all mortars were the same, The British 3in mortars were just about the worst. British troops loved using captured Italian mortars and using Italian bombs in British barrels, at least until the barrels bulged and base plates bent. Just because they were making a better mortar and bomb in the early 30s than they did in 1918 doesn't mean they should have stopped improving things.
When the Italians have more mortars per battalion and they almost out range the British 3in by about 2 to 1 it means the British need to something else to counter the Italian mortars. Like 25pdr guns.
If you look at the American 81mm mortar on the naval mount it could be either drop fired or trigger fired, but it had to be muzzle loaded ( tip barrel up to at least 30 degrees and drop bomb in the muzzle). You can figure out how to breech load it and you can load at less than 30 degrees but something is going to go up and not just cost.

People knew about bigger mortars. They just weren't quite sure what to do with them. They started needing a lot more transport. With the size of the crews and size of the truck needed and the size/amount of transport needed some armies figured that they should spend the money on artillery. Or at least use large mortars to to equip artillery units and not try to foist them off on the infantry.

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When you make bigger better mortars they have a longer range so their support becomes able to cover beyond the regimental level and need to be allocated between more targets so need to be controlled by a higher level to make best use of them and incorporating them under artillery rather than infantry is logical. The next step is the infantry battalions see a need to retain an organic local area fire support and get 81mm mortars and the cycle repeats. The limit for the battalion level mortar is to be man portable by the crew. The same limitation as the Universal Carrier was built around, ie the load must be made of man portable items.

One reason the British loved their 2 inch mortars was that they stayed with the infantry and no one was going to group them in a higher formation, so the platoon always had indirect fire support and the troops got very skilled with them even with just a painted white line and eyeball judgement to aim them.

Thus we saw three classes. The 2 inch that can be carried complete by one man, the 3 inch that can be broken down into man portable sections and the 4.2inch which has to be carried into position by a vehicle. Or 61, 81 & 120mm if you prefer.

A few pics from my collection

tomo pauk said:

Quirk with this system is that one still uses the off-the-shelf ammo.
RT-20 was supposedly doing 850 m/s, despite the short barrel and the divertion of small % of the gasses.

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I finally found it. Typically a barrel of this length will give you around 830m/s using regular 20x110mm ammo,
while the RT-20 has only 620 m/s.
RT20: Croatia's Insane Kludged 20mm Anti-Material Rifle - Forgotten Weapons
The main purpose of this "vent" is to lower muzzle energy, the recoil cancelation is a secondary effect.
The design lacks a proper venturi nozzle and the propellant does not burn completely.
The backblast is huge and reveals the shooter's position.
Quick and dirty solution, typical wartime improvisation.

It would seem, for the US Army in WW II anyway, that an 81mm mortar squad consisted of 8 men.
This includes 18 rounds of 'light' bombs. Please note that 6-7 men are carrying 15-20kg loads of weapons/ammo and are not carrying much personnel equipment (shelter-tents, blankets, rations, etc). It is possible to man carry 81 mortars, lots of armies do it/have done it. But if you are going very far or for very long (several days even) you need a lot more men than the table of organization shows, a an awful lot more.

Logistics required for an 81mm mortar battery are/were probably in the ballpark of the logistics required for the same number of barrels of the 75mm infantry guns. The mortar ammo will be lighter than the 75mm ammo on average, but you will be taking the advantage of the very nice RoF that mortar offers.

In the US infantry battalion TOE, there was an ammunition and pioneer platoon whose function was in part as its denomination implies, to provide ammunition.

tomo pauk said:

Logistics required for an 81mm mortar battery are/were probably in the ballpark of the logistics required for the same number of barrels of the 75mm infantry guns. The mortar ammo will be lighter than the 75mm ammo on average, but you will be taking the advantage of the very nice RoF that mortar offers.

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Ballpark is a good description
Infantry guns are much more accurate (WWII) and need a lot fewer rounds for point targets, like bunkers, weapons pits, etc. When you are trying to hit a large area (several hundred meter hill top?) and accuracy is not that important the lighter/faster firing mortars can do the same job for less total weight. It is a trade off.

Frog said:

In the US infantry battalion TOE, there was an ammunition and pioneer platoon whose function was in part as its denomination implies, to provide ammunition.

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An 81mm mortar can fire 15-18 rounds per minute at sustained rate. It can fire much faster rapid fire but not for long, rounds start cooking off before they reach the bottom of the tube.
You need 16-17 men to move 100 mortar bombs very far on foot. US had six 81mm mortars per battalion.
They did move mortars and ammo by foot (back/chest) but without trucks or horses/mules you needed to start getting the regular infantry to help lug the ammo. Special operation/s not regular practice.
Same for infantry guns.

How does that stack of ammo of ammo on the right weigh?

1 mm mortar platoon had a jeep and trailer for hauling ammunition, plus each mortar squad had several M4 hand carts for moving the mortar and a another cart or two for moving the ammunition.

John Mo Mule said:

1 mm mortar platoon

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I've heard of the 'needle guns', but, darn

In a more affirmative tone, here is the video about the shotgun slug that has rocket assist. It adds another 500 ft/s to the 1500 ft/s 'base' MV of the shotgun, according to the author/narrator of the video. Ignition & burn of the rocket motor happens in the barrel in this case.

I would really like to see a little more in depth look at the ballistics.
A normal 12 gauge slug is good for about 1500fps with a 1 ounce (28.35 gram) projectile.
One US company is advertising 2000fps with a 300 grain (19.44 gram) discarding sabot projectile.
In the video they say the rocket projectile was about 1/2 ounce ( 14.2 grams) but even if they are off by several grams it doesn't seem that the rocket actually did much?

tomo pauk said:

Ignition & burn of the rocket motor happens in the barrel in this case.

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So it is just an additional "powder", much more efficient because it needs to provide only pressure, not momentum as in the proper rocket engine.

This might've been also posted in another current thread - the quick comparison of size, and potential & realistic power of the respective guns.
(mntn - mountain; rgmntl - regimental; never mind the different color of the text I've inserted in)



In order to get from the F-22 to the Pak-36(r), one of changes was the bored-out rear part of the barrel so the more powerful cartridge can get in. And it was plenty powerful, with propellant charge being of up to 2.6 kg (vs. the F-22 using max of 1.4 kg, and F-34 using just 1.08 kg).

tomo pauk said:

This might've been also posted in another current thread - the quick comparison of size, and potential & realistic power of the respective guns.
(mntn - mountain; rgmntl - regimental; never mind the different color of the text I've inserted in)

View attachment 811069

In order to get from the F-22 to the Pak-36(r), one of changes was the bored-out rear part of the barrel so the more powerful cartridge can get in. And it was plenty powerful, with propellant charge being of up to 2.6 kg (vs. the F-22 using max of 1.4 kg, and F-34 using just 1.08 kg).

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AI Translation

tomo pauk May be of interest to you.

I returned to the French military archives at Vincennes today. The bulk of the new content was reports from the meetings of the Consultative Committee on Armaments which are a way to see the overall view of French Army weapon programs.

Not much on AT per se, but it may be of interest that the 3rd May 1937 mentioned that the new improved 37mm light tank gun (what would become the SA38) was to be showcased in June with two projectiles:
- one fullbore 900g proj shot at 590/600 m/s with ballistic cap (competing with 700g no ballistic cap proj shot at 680-700 m/s which would become the service round)
- one new type made with a 25mm core, "sheathed" (I interpret that as APCR rather than APDS) shot at 900 m/s and thus near identical performance to the 25mm AT gun.

So subcaliber rounds for guns more powerful than the 37mm SA18 did start even earlier than I thought.

The matter of an improved 75mm gun to replace the mle.97 was also discussed in 37/38 and now I understand it led to the TAZ version we know of. It came up as a response to the failed 75 mle.33 carriage which was not suitable for proper antitank use (incompatible with a good sight), was not suitable for fast towing and was too heavy.

This involved two steps: first a new carriage suitable for fast towing (maximum complete gun weight: 1500kg), 60° horizontal traverse if I recall, fitted with appropriate sights for antitank and field artillery use (might be a single sight combining both uses). This had priority since while the barrels may last a long time in wartime, the old carriages would be work in 6 months.

2nd step was a thoroughly modern barrel which would maintain a maximum range close to 14km and thus a velocity of 600 m/s for HE, would be lighter, have a longer life, capable to shoot at high rates for longer periods, and easy and quick to change in the field. It would also be capable of shooting AP at a greater velocity than the mle.97. As of 1937, the obsolete "Obus P" (75mm mle.1910 APHE) was to be replaced by the capped "Obus R" in development which offered interesting antitank performance even compared to the 47 AT gun while carrying a bursting charge.

The 360° TAZ carriage came later and was allowed assuming an extra weight of no more than 15% (225kg extra then, 1725kg total weight limit). The French TAZ carriage concepts stemmed from a notion that tanks may come from any direction and also that they were becoming faster and thus may be hard to follow with a limited traverse gun.

There is a passing mention that the 37mm casemate gun was better at AT than the 47mm tank gun and indeed "that a 37mm gun of the same length as the 47 tank gun would have the same penetration but would have the advantages of the smaller caliber". This is more relevant for the other thread on tank guns however, and it didn't lead to anything.

More archive digging this week indicates that the Ateliers de Constructions of Bourges, Puteaux and Le Havre all worked on new 75mm field guns (the 75 TAZ for Bourges). While the original mle 97 barrel was the fallback option, these projects focused on a new barrel with a muzzle velocity of 640 m/s (75 M3 analogue).
Both Bourges and Le Havre were also working/ordered to work on a 700 m/s barrel, this time using a new case of intermediate dimensions between the 350R case of the mle 97 and the mle.1928 case. The end result would be a gun that has only a 15 m/s slower muzzle velocity, but possibly a disproportionately shorter case (especially convenient for tank installation).

The 80mm 1000 m/s AA gun design from Bourges that I mentioned in another thread could be a suitable basis for a very powerful late war antitank/tank gun. The 90mm 1075 m/s AA gun would be just as inconvenient to use in these roles as the very long American late war projects.

Meanwhile, as of November/December 1939, Mr Edgar Brandt was working on an ominous 25mm AT gun rebored to 37mm, expected to achieve 940 m/s (probably with subcaliber ammo given the raw ballistic weakness of a rebored 25mm barrel and necked out case), but with the recoil brake possibly only strong enough to handle 850 m/s. This was tied to continuing research from Brandt on subcaliber ammo, including with tungsten carbide cores instead of steel this time.

Elan Vital said:

More archive digging this week indicates that the Ateliers de Constructions of Bourges, Puteaux and Le Havre all worked on new 75mm field guns (the 75 TAZ for Bourges). While the original mle 97 barrel was the fallback option, these projects focused on a new barrel with a muzzle velocity of 640 m/s (75 M3 analogue).
Both Bourges and Le Havre were also working/ordered to work on a 700 m/s barrel, this time using a new case of intermediate dimensions between the 350R case of the mle 97 and the mle.1928 case. The end result would be a gun that has only a 15 m/s slower muzzle velocity, but possibly a disproportionately shorter case (especially convenient for tank installation).

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Somebody had missed the larger caliber memo?
Building improved 75mm field guns when at least 3 of the major players were building/planning 88-105mm guns as 'standard' is actually poor planning at high levels (command).
The larger guns gave up a bit of range for much greater shell/explosive weight for not only the gun but the tow system (horse/motor/tracks) and for the man power invested in the gun batteries/battalions.

Elan Vital said:

The 80mm 1000 m/s AA gun design from Bourges that I mentioned in another thread could be a suitable basis for a very powerful late war antitank/tank gun. The 90mm 1075 m/s AA gun would be just as inconvenient to use in these roles as the very long American late war projects.

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Again they were following a bad path. High velocity was a goal followed by a number of countries so they were not alone. But High velocity was to improve accuracy by shortening flight times. Unfortunately high velocity means very high barrel wear, and worn barrels both lose velocity and accuracy quickly.
For AT work such a gun would be very powerful but as the US, British and Germans found out, very difficult to move. The British 17pdr being about 3 tons for 900m/s gun. The weight penalty in not linier. A 10% increase in velocity often needs 20% more propellent, long barrel, larger breech and larger gun carriage (recoil increase is somewhat more than 10%).

Elan Vital said:

Meanwhile, as of November/December 1939, Mr Edgar Brandt was working on an ominous 25mm AT gun rebored to 37mm, expected to achieve 940 m/s (probably with subcaliber ammo given the raw ballistic weakness of a rebored 25mm barrel and necked out case), but with the recoil brake possibly only strong enough to handle 850 m/s. This was tied to continuing research from Brandt on subcaliber ammo, including with tungsten carbide cores instead of steel this time.

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this was a very promising path, it just didn't have enough time. It really needed the tungsten carbide core to work.
Using a steel penetrator only works at rather close ranges. The small steel projectile just sheds velocity too fast for longer range work.

The historic French tank guns of 1940 were pretty weak things and any improvement would help, but what was really needed was a decent 47-57mm gun with around 800-900m/s firing a decent (APCBC) projectile. This would work on anything short of a Tiger tank until 1942 and do it out to 1500-2000 meters.
A trick APDS round using tool steel will not work at the longer ranges.

Shortround6 said:

Somebody had missed the larger caliber memo?
Building improved 75mm field guns when at least 3 of the major players were building/planning 88-105mm guns as 'standard' is actually poor planning at high levels (command).
The larger guns gave up a bit of range for much greater shell/explosive weight for not only the gun but the tow system (horse/motor/tracks) and for the man power invested in the gun batteries/battalions.

Again they were following a bad path. High velocity was a goal followed by a number of countries so they were not alone. But High velocity was to improve accuracy by shortening flight times. Unfortunately high velocity means very high barrel wear, and worn barrels both lose velocity and accuracy quickly.
For AT work such a gun would be very powerful but as the US, British and Germans found out, very difficult to move. The British 17pdr being about 3 tons for 900m/s gun. The weight penalty in not linier. A 10% increase in velocity often needs 20% more propellent, long barrel, larger breech and larger gun carriage (recoil increase is somewhat more than 10%).

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France identified the need for short higher caliber howitzers in the 1922 and later programs. Studies slowed down to a crawl up to the early 30's due to the post-WW1 reconstruction and Franc crises.

By the early 30s, they got a 90mm Bourges and then 105mm designs from Schneider and Bourges. The 90mm was abandonned, the Schneider was built in low numbers due to its complication. The Bourges 105 was ordered in numbers but not many entered service by mid 1940 (232) due to artillery construction being slowed down or suspended in favor of AT and AA guns which were in high demand. Given that France was supposed to brace for a German air and mechanized offensive and had a decent artillery stockpile, focusing on counters to the offensive made sense.

Once things bog down again and new capacity is opened while the deficiencies in AT (already almost complete in mid 40) and AA guns are plugged, 105mm short and long guns would certainly rise in priority. In any case the designs were already there and in production.

With the 105 working alongside the 75, it is no wonder that the French prioritized improvements in antitank capability for new 75mm. Rather than being a field gun with antitank capability like the 25 pounder (and even then 18 and 25pdr only got AP developped in 1940), it would be fairer to say the 75 were AT guns with backup indirect fire capability.

The high velocity AA guns were probably on the wrong path, but the French weren't completely alone in this (FlaK 41). They are certainly very difficult to use as towed AT. Use in self-propelled or tank form is far more likely as evidenced by the study of a SP naval 75mm or 90mm as very powerful AT weapons started in April 1940, and the early 1941 Vichy era ideas for a 90mm casemated SPG.

Shortround6 said:

Again they were following a bad path. High velocity was a goal followed by a number of countries so they were not alone. But High velocity was to improve accuracy by shortening flight times. Unfortunately high velocity means very high barrel wear, and worn barrels both lose velocity and accuracy quickly.
For AT work such a gun would be very powerful but as the US, British and Germans found out, very difficult to move. The British 17pdr being about 3 tons for 900m/s gun. The weight penalty in not linier. A 10% increase in velocity often needs 20% more propellent, long barrel, larger breech and larger gun carriage (recoil increase is somewhat more than 10%).

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High velocity 80mm and greater AA and AT guns were great. Thus that path was the correct one.
Unfortunately, French were too late to that path.

Shortround6 said:

this was a very promising path, it just didn't have enough time. It really needed the tungsten carbide core to work.
Using a steel penetrator only works at rather close ranges. The small steel projectile just sheds velocity too fast for longer range work.

The historic French tank guns of 1940 were pretty weak things and any improvement would help, but what was really needed was a decent 47-57mm gun with around 800-900m/s firing a decent (APCBC) projectile. This would work on anything short of a Tiger tank until 1942 and do it out to 1500-2000 meters.
A trick APDS round using tool steel will not work at the longer ranges.

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IIRC the main problem the steel-cored ammp was that there was a great danger of the cores shattering at the great impact speeds. A thing that tungsten alloys had far less problems.
French have had the 47mm gun firing the APCBC projectile, and at good MV, but such the gun was available only in the towed and casemate installations. The tank gun was weaker (but still good enough for 1940).

tomo pauk said:

High velocity 80mm and greater AA and AT guns were great. Thus that path was the correct one.

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The successful, at least in terms of huge production volumes, WWII era AA guns in this size class, in particular the German 88 flak 18/36/37, UK 3.7", US 90mm, USSR 85mm, all had MV between 790-840 m/s.

Going for >1000m/s with 1930'ies metallurgy was probably biting off more than one can chew.

re

Shortround6 said:

Using a steel penetrator only works at rather close ranges. The small steel projectile just sheds velocity too fast for longer range work.

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and

tomo pauk said:

IIRC the main problem the steel-cored ammp was that there was a great danger of the cores shattering at the great impact speeds. A thing that tungsten alloys had far less problems.

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A well made alloy steel APC or APCBC projectile (ie a projectile with a penetrator cap and manufactured under good cuality control) can function effectively upto about 1000 m/sec - as witnessed by the 88mm L/71 to L/74 series of guns, which fired APCBC rounds at ~1000 m/sec.

Part of the French sub-caliber round initiative involved firing more-or-less standard APCBC rounds from a larger caliber gun. One of the types being developed, that was tested before(during?) the war, was a 75mm gun firing a 47mm APCBC round. The higher MV of the 47mm APCBC when fired as a sub-caliber round allowed it to penetrate the same amount of armour at 1000m as the same round did at 600m when fired from the normal 47mm gun. Yes, the sub-caliber steel projectile shed velocity faster than a TC core of the same dimensions would have, but since it started out at a significantly higher MV it still had a useful impact velocity at longer range.

The problem of alloy steel rounds shattering at high impact velocity was not encountered as the impact velocities for the 47mm sub-caliber rounds were below the 1000 m/sec limit. The problem of shattering at higher velocities at shorter ranges was to have been dealt with by firing the standard 75mm APCBC at the normal MV.

Apologies, this is all from my notes and I do not remember/did not record which specific guns they were talking about.