Alternative light and anti-tank guns, 1935-45

[yulzari]

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.

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.

 

[Jimbob]

A few pics from my collection

 

[peceed]

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.

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.

 

[Shortround6]

It would seem, for the US Army in WW II anyway, that an 81mm mortar squad consisted of 8 men.

90th IDPG: Tableau Number 1 - The 81mm Mortar Squad

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.

 

[tomo pauk]

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.

 

[Frog]

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.

 

[Shortround6]

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.

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.

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.

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?

 

[John Mo Mule]

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.

 

[tomo pauk]

1 mm mortar platoon

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.

 

[Shortround6]

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?

 

[peceed]

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

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.

 

[tomo pauk]

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).

 

[marathag]

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).

AI Translation

 

[Elan Vital]

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.