Alternative light and anti-tank guns, 1935-45

[Shortround6]

One might note that the 1841 zündnadelgewehr or Dreyse Needle Rifle used a lead egg shaped bullet in a wrapped paper sabot. The standard Prussian infantry rifle until after the 1870 War.

And accuracy well and truly sucked.
Dreyse bullets may have been composite rigid sabot and not discarding sabot?

 

[Shortround6]

You don't have a lot of APDS in the 1939/40 because people didn't designed and have it manufactured?

Tungsten, even for tool steel (around 7% alloy in the steel?) or for tungsten carbide cutting tools was not common, despite known advantages for cutting tools due to cost/supply.
Firing large lumps of it out of cannon barrels is a pretty expensive use. Germany was getting a decent percentage of it's Tungsten form Portugal. French access may have been better?
The Famous US 76mm APCR shot of 1944 was usually issued at rate of 2-4 rounds per tank by the "book". Some tanks didn't see any for a few weeks at a time but if they didn't see a Tiger or Panther for those days/weeks I guess it didn't make any difference.

If one does not push beyond 1000 m/s with the APDS - and most non-AA and non-Navy guns will not in that time - one can do with hardened steel.

Only at a significant reduction in armor penetration.

Penetration is energy applied to the target area.
Energy is mass (weight) times velocity squared.
Tungsten carbide is just about twice the density of steel. So a steel penetrator core of the same shape is about 1/2 as heavy and has 1/2 the energy at the same velocity.

Now we can try to get around this by using a larger core, length or width or both?
We can try to fire the lighter core at a higher velocity or combine using the larger penetrator.

Problems are that a longer penetrator requires a quicker rifling twist. Quicker twists raise pressures slightly, Quicker twists may require different HE shell construction (heavier walls or better steel).
At short range you may be able to come up with acceptable work arounds.
A long range the heavy for it's size TC penetrator offers significantly better long range ballistics in time of flight/drop and penetration. Assuming you can solve the accuracy problem of the discarding sabot.

 

[tomo pauk]

Tungsten, even for tool steel (around 7% alloy in the steel?) or for tungsten carbide cutting tools was not common, despite known advantages for cutting tools due to cost/supply.

Steel.
Make the cores from steel at 1st (say, late 1920s as experiment, and by mid-1930s for service), and move to tungsten when/if needed & available.

Problems are that a longer penetrator requires a quicker rifling twist. Quicker twists raise pressures slightly, Quicker twists may require different HE shell construction (heavier walls or better steel).
At short range you may be able to come up with acceptable work arounds.
A long range the heavy for it's size TC penetrator offers significantly better long range ballistics in time of flight/drop and penetration. Assuming you can solve the accuracy problem of the discarding sabot.

Problems exist to be solved. Using the best part of the 1930s to figure out the details and intricacies is a far cry vs. trying to solve the problems within the months of a brutal major war.

 

[SaparotRob]

And accuracy well and truly sucked.
Dreyse bullets may have been composite rigid sabot and not discarding sabot?

Sabotage?

 

[yulzari]

And accuracy well and truly sucked.
Dreyse bullets may have been composite rigid sabot and not discarding sabot?

The not very good at discarding sabot. Supposed to discard and often did, but not always. Very much a prisoner of the materials and manual skill of the paper coiling sabot maker. The bullet was supposed to fly free.

 

[Shortround6]

Steel.
Make the cores from steel at 1st (say, late 1920s as experiment, and by mid-1930s for service), and move to tungsten when/if needed & available.

Problems exist to be solved. Using the best part of the 1930s to figure out the details and intricacies is a far cry vs. trying to solve the problems within the months of a brutal major war.

A big hindrance to the development of high tech AP projectiles was the very real lack on need in the 1920s and 30s. Until the late 30s and the deployment of the Char B1 tank with it's 40mm armor (the B1 Bis didn't show up until early 1937) a decent 37-47mm gun with fairly standard AP ammo would take care of things. I am emphasizing decent as the German 37mm was not and neither were either of the French 37mm or the French tank mounted 47mm guns.
A Czech 47mm has a decent chance against the side of a Char B1 Bis from the side at around 500 meters with standard steel shot.
It was interesting to fool around with advanced projectiles but the actual need was not there until the late 30s. And a decent answer to a 28-35 ton tank was a 1 ton AT gun and not a 1/2 ton gun firing rare metal (for it's day) shot. Germans got all caught up in the technical answer (AP40 Shot) which bit them in the ass when the Soviets didn't give up in late 1941 and the Germans started running out of tungsten.
If you are going to bet your ass on trick ammo you better have a good source of supply for the raw materials.

 

[tomo pauk]

A big hindrance to the development of high tech AP projectiles was the very real lack on need in the 1920s and 30s. Until the late 30s and the deployment of the Char B1 tank with it's 40mm armor (the B1 Bis didn't show up until early 1937) a decent 37-47mm gun with fairly standard AP ammo would take care of things. I am emphasizing decent as the German 37mm was not and neither were either of the French 37mm or the French tank mounted 47mm guns.
A Czech 47mm has a decent chance against the side of a Char B1 Bis from the side at around 500 meters with standard steel shot.
It was interesting to fool around with advanced projectiles but the actual need was not there until the late 30s. And a decent answer to a 28-35 ton tank was a 1 ton AT gun and not a 1/2 ton gun firing rare metal (for it's day) shot. Germans got all caught up in the technical answer (AP40 Shot) which bit them in the ass when the Soviets didn't give up in late 1941 and the Germans started running out of tungsten.
If you are going to bet your ass on trick ammo you better have a good source of supply for the raw materials.

Seem like the mid-power 75-76mm gun still had it's place These could've been had at around 1000 kg with a bit care (muzzle brake, light undercarriage legs).

Wrt. the decent 37-47mm guns - that is quite a broad range of weapons. The best 47mm gun, like the French gun, will be a whole another league vs. a decent 37mm (talk Bofors AT gun), and Germans only acquired the 47mm AT gun when they conquered Czechia.
An AT gun should be somewhat future-proof, like all the weapon types should be. Granted, the armies of the day were not having decades of the experience, but they can take a look at the development of ships and aircraft to see the pattern of ever-tougher targets appearing, as well as the meant to deal with these targets.
The AP 40 was a way of keeping the existing and future AT guns relevant. Perhaps it was a mistake that there was no APCR with the hardened steel penetration for the all of the guns, and see whet works? That the Germans passed on the mid-power 75mm guns as anti-tank guns, at least for the motorized units, was a mistake on their part. Also on the Stugs and other. A smaller mistake, but still, was that they didn't picked up on the Czech 47mm gun in a more substantial way. Their mistake was also that the 88mm L56 ordnance was not mated to the 105mm carriage by 1940.

 

[Shortround6]

An AT gun should be somewhat future-proof, like all the weapon types should be. Granted, the armies of the day were not having decades of the experience, but they can take a look at the development of ships and aircraft to see the pattern of ever-tougher targets appearing, as well as the meant to deal with these targets.

Navies had been working on better armor and better projectiles since about 1860
The APCBC rounds date to before WW I but they cost more money than plain steel shot and they don't work much better at very close range. They work a lot better at further ranges. Close and far is relative with 47mm guns and 13.5 in guns

The AP 40 was a way of keeping the existing and future AT guns relevant. Perhaps it was a mistake that there was no APCR with the hardened steel penetration for the all of the guns, and see whet works?

AP 40 was one thing, the whole side track with taper bore guns (28/20, 42/28 and 75/55mm) was a path that did not need to be followed.
Steel does not work anywhere near as well once you are not fooling around trying to make grenade throwers (French short 37mm guns) into anti-tank guns.

You need a certain amount of mass per sq cm of target area at the desired velocity. Tungsten Carbide gives double the mass for the same volume. Trying to use even tool steel does not solve the mass to target area problem..............unless you use a really long core, which brings up other problems.
British 17pdr APDS

What do you have to do to get a core weight close to the same as the Tungsten carbide core?
If you use a steel core you loose a lot of weight and you can't increase the velocity enough to compensate. The much lighter projectile will exit the barrel before getting the needed velocity.
As a real world check the 30-06 rifle cartridge has been offered with bullets from 220 grains to 100-110 grains from factories and Remington offered a 55 grain bullet in a plastic discarding sabot. The 220 grain bullets could hit around 2300-2400fps depending on barrel and powder. The 110 grain bullets did around 3300-3400fps and Rem claimed 4080fps for the sabot load. Not quite twice the velocity for 1/4 the bullet weight. It has about 80% of the energy of the 220 grain bullet which is also not quite optimal.
Most artillery follows the cube law. When you go from a 57mm round to a 75mm round you not only have the increase in diameter which gives you the increase in area being a square of the diameter but just about everybody increased the projectile's length in proportion to the increase in caliber so the 75mm shells will be about 30% longer than a similar 57mm shell and have 30% more weight per unit of frontal area which gives 30% more penetration at the same velocity. Another thing is that the extra 30% weight for the same frontal area is why the larger shells retain velocity better for long range work.
It is this weight to diameter that really screws up APCR rounds and why APDS with tungsten carbide beats the heck of regular plain steel at long range.
A steel penetrator doesn't work for crap in an APCR round for distance and even with an APDS out of a medium (2000fps with full bore shell) 75mm are you going to get any better performance than the 57mm AT gun with 2600-2700fps velocity?

 

[tomo pauk]

AP 40 was one thing, the whole side track with taper bore guns (28/20, 42/28 and 75/55mm) was a path that did not need to be followed.

Very true.
OTOH, when someone says 'AP 40 shot', that usually means a cored projectile for the 'normal' guns, not the projectiles for the squeeze bore guns

Steel does not work anywhere near as well once you are not fooling around trying to make grenade throwers (French short 37mm guns) into anti-tank guns.

A steel cored projectile fired from a Fench 75mm gun or it's equivalent still offers the increase of muzzle velocity and increased chance to hit a moving tank. With 900 m/s give or take MV (and obviously ever lower at 200-300-500-700m distances), it should be still under the velocity threshold for steel to shatter. Experiment with the idea and execution; if the shatter is still there, move to a bit heavier projectile to decrease the MV a bit. Experiment with tungsten tip and hardened steel shaft if/when there is enough of tungsten to be had.

What do you have to do to get a core weight close to the same as the Tungsten carbide core?
If you use a steel core you loose a lot of weight and you can't increase the velocity enough to compensate. The much lighter projectile will exit the barrel before getting the needed velocity.
As a real world check the 30-06 rifle cartridge has been offered with bullets from 220 grains to 100-110 grains from factories and Remington offered a 55 grain bullet in a plastic discarding sabot. The 220 grain bullets could hit around 2300-2400fps depending on barrel and powder. The 110 grain bullets did around 3300-3400fps and Rem claimed 4080fps for the sabot load. Not quite twice the velocity for 1/4 the bullet weight. It has about 80% of the energy of the 220 grain bullet which is also not quite optimal.
Most artillery follows the cube law. When you go from a 57mm round to a 75mm round you not only have the increase in diameter which gives you the increase in area being a square of the diameter but just about everybody increased the projectile's length in proportion to the increase in caliber so the 75mm shells will be about 30% longer than a similar 57mm shell and have 30% more weight per unit of frontal area which gives 30% more penetration at the same velocity. Another thing is that the extra 30% weight for the same frontal area is why the larger shells retain velocity better for long range work.
It is this weight to diameter that really screws up APCR rounds and why APDS with tungsten carbide beats the heck of regular plain steel at long range.

All good.

A steel penetrator doesn't work for crap in an APCR round for distance and even with an APDS out of a medium (2000fps with full bore shell) 75mm are you going to get any better performance than the 57mm AT gun with 2600-2700fps velocity?

A mid-power 75mm, that we have in hundreds or in thousands, beats the cr@p of the high-power 57mm gun that we don't have - most of the armies were reasonably well equipped with such 75/76mm guns already in the 1920s and 30s, but nobody have had the high-power 57mm guns. Most armies didn't even have the high-power 47 or 50 mm guns.

 

[Shortround6]

A mid-power 75mm, that we have in hundreds or in thousands, beats the cr@p of the high-power 57mm gun that we don't have

Problem is that just about all of those hundreds or thousands of mid powered 75mm guns don't have..
1. Sight suitable for anti-tank work.
2. One man gun laying, that is one man controlling both elevation and traverse but since................
3. Most of these guns have really crappy traverse, 8 degrees at the most and the French guns had 6 degrees?
4. A high gun shield or silhouette.

This is just the physical problems, some of which are not hard to solve, some are.

Tactical deployment problems, aside from the limited traverse.
Guns placed in the front lines, or within 1000yds of the front lines to shoot at tanks are too close to use as general artillery support. If they fire they revival their position/s are a prime target for counter battery fire (or being targets by 81mm mortars).
Guns scattered about as AT guns may not be hooked up to the field phones for even answering calls for general artillery support. Depends on time spent emplaced and a particular armies signals capability.
Guns doing general fire support are too far from the front lines to deal with tanks unless they have broken through and penetrated 3-5 km or more.
Having a few good AP shells can help the batteries defend themselves from being overrun but that is not really acting as AT guns.

Germans grabbed the Soviet 1936 field guns because they were both powerful and they had 60 degree traverse. The Germans changed the elevation wheel over to the left side of the carriage for one man gun laying. The Germans did not try to convert any older 76mm field guns.

With a 60 degree traverse a gun can cover and arc 1047 meters at 1000 meters from the gun.
With an 8 degree traverse a gun can cover an arc 140 meters at 1000 meters from the gun.
With a 6 degree traverse a gun can cover an arc 105 meters at 1000 meters from the gun.

 

[tomo pauk]

Problem is that just about all of those hundreds or thousands of mid powered 75mm guns don't have..
1. Sight suitable for anti-tank work.
2. One man gun laying, that is one man controlling both elevation and traverse but since................
3. Most of these guns have really crappy traverse, 8 degrees at the most and the French guns had 6 degrees?
4. A high gun shield or silhouette.

This is just the physical problems, some of which are not hard to solve, some are.

Advantage is that the most expensive part of the guns - barrel, cradle, locking system and hydraulic system - are paid for. Advantage is also that there are tens of thousands of shells in the warehouses, some, like the HE and shrapnel, don't have an equivalent in power in the 57mm bracket (let alone the 47-50mm). Even the AP ammo is there, or it will not be hard to make. Many countries even don't have the 57mm barrel-making machines.
Sights for direct fire vs. the moving target will need to be made anyway, same for the split carriage. Retrofit of the split carriage helps the remaining guns across the board, not only the guns earmarked for the AT units.

Tactical deployment problems, aside from the limited traverse.
Guns placed in the front lines, or within 1000yds of the front lines to shoot at tanks are too close to use as general artillery support. If they fire they revival their position/s are a prime target for counter battery fire (or being targets by 81mm mortars).
Guns scattered about as AT guns may not be hooked up to the field phones for even answering calls for general artillery support. Depends on time spent emplaced and a particular armies signals capability.
Guns doing general fire support are too far from the front lines to deal with tanks unless they have broken through and penetrated 3-5 km or more.
Having a few good AP shells can help the batteries defend themselves from being overrun but that is not really acting as AT guns.

The guns in the AT units will have different priorities than the guns in the artillery units.
Having the AP shots in the field artillery arsenal is a prudent thing to do, so is having the good direct-fire sights. Germans were over-running the Polish artillery positions with light tanks - very easy if the enemy does not have the means and training to deal with tanks. In 1940, during the battles around Arrass and Abbeville, German 105mm howitzers - the most unlikely AT guns - were used against the tanks to a good effect.

Germans grabbed the Soviet 1936 field guns because they were both powerful and they had 60 degree traverse. The Germans changed the elevation wheel over to the left side of the carriage for one man gun laying. The Germans did not try to convert any older 76mm field guns.

The F22 gun was rated by for 1400g of propellant. The older guns were not, their max was 1080g; the 1400g charge was to be used there in dire emergencies.

 

[Shortround6]

Advantage is that the most expensive part of the guns - barrel, cradle, locking system and hydraulic system - are paid for.

True, but most armies of the 1930s didn't have enough guns to equip the field artillery units that they wanted.
A lot of the left over WW I guns were not in good shape and many were scrapped in the years following the war with armies keeping the guns/carriages that were in the best condition.
Training used up some guns and different economic problems delayed or canceled improvement/refurbishment plans. US did better than others as far as mounting old guns on new carriage's. France planned to but didn't get very far. France also had a real problem with their artillery program. It took way too long for them to decide that the French 75 was NOT the "be all and end all" to the artillery question and that some 105mm howitzers might actually be a good idea to have in the army. Production of several hundred 105mm howitzers sucked up a fair amount of the French artillery budget in the mid/late 30s. In typical French fashion of the time production was both slow and split between two different designs.

In 1934 the French apparently believed that trucks were passing fad.
The French did not have the number of 75mm guns needed for the expanding French army of the mid to late 30s. Swiping the field guns to make AT guns out of them just moves the problems to a different area.
Yes having AP shot in the artillery batteries for self defense is/was a good idea.

 

[tomo pauk]

In 1934 the French apparently believed that trucks were passing fad.

Some of the German interwar guns were also archaic-looking

The French did not have the number of 75mm guns needed for the expanding French army of the mid to late 30s. Swiping the field guns to make AT guns out of them just moves the problems to a different area.

In the 1930s era and French budget: would it be more prudent to them to make 105mm howitzers in order to have the surplus of 75mm field guns that can be turned into the AT guns, or to make 57mm AT guns while leaving the field artillery capabilities pretty much at the level of 1918?

 

[GTX]

I find the Madsen 20 mm AA Machine Cannon M/38 to be interesting. While not so much an alternative since it did exist, perhaps in greater use. As previously posted elsewhere, reportedly the Madsen F5 version was designed as an anti-tank gun. It supposedly was a fully automatic weapon, with a 15-round magazine. At 100 m, it was able to pierce 42 mm of armour, and 32 mm at 500 m.

While perhaps not spectacular against later war tanks, for 1935 - 40/41 against the likes of the Panzer I/II/III/IV and their Italian/Japanese equivalents it would have been effective, especially if not only going against frontal armour. And consider:

• Panzer I armour thickness: 7–13 mm
• Panzer II armour thickness: 5–15 mm
• Panzer III armour thickness: 15–30 mm
• Panzer IV armour thickness: 15–30 mm
• Panzer 35(t) armour thickness: 8–25 mm
• Panzer 38(t) armour thickness: 8–30 mm

 

[Shortround6]

In the 1930s era and French budget: would it be more prudent to them to make 105mm howitzers in order to have the surplus of 75mm field guns that can be turned into the AT guns, or to make 57mm AT guns while leaving the field artillery capabilities pretty much at the level of 1918?

What would have been prudent was to make 37-47mm AT guns and at the upper end, something a little smaller and lighter than the 47mm they did make.

an over 1000kg AT gun was not really needed in 1940 or even for much of 1941 and parts of 1942.
The 25mm AT gun was a bit too much gun (size and weight) for the actual performance and it was a single purpose gun. If it had HE it wasn't very good. The 37mm guns were grenade throwers and the 45-47mm guns were large grenade throwers but they were often used as infantry support guns.
The AT guns needed to be able to be moved by men (crew) at least for short distances and 1000-1500kg guns need very favorable circumstances for that to be possible.

France had several facilities capable of making all sizes of cannon. Perhaps duplication of effort but in theory they could select the best gun or combine features (with enough time), and not have to settle on one answer.

As noted by GTX, German tanks did not have very thick armor and until the Tiger shows up, The Germans did not exceed 60mms on the front ( hull of the III H) or 30mm on the side.
French were building an AT gun to fight their own tanks, which is prudent, but perhaps they over did it?

 

[tomo pauk]

What would have been prudent was to make 37-47mm AT guns and at the upper end, something a little smaller and lighter than the 47mm they did make.
an over 1000kg AT gun was not really needed in 1940 or even for much of 1941 and parts of 1942.

That is the kicker - a smaller, lighter and less powerful 47 mm, or a powerful 37mm gun is not an equivalent of a 57mm gun as powerful as the 6pdr, nor of the French 75 - and discussion on this last page was about the later two guns as competing for the same role.
I'm glad that you find the not-so-powerful 47mm guns at your liking after all these years

The 25mm AT gun was a bit too much gun (size and weight) for the actual performance and it was a single purpose gun.

While I agree on the single purpose gun comment (there seems to be no HE shell issued, at least not by the French), I disagree with the 1st part. Penetration was barely worse than that of the 37mm pak, and it was more than enough to do it's job - pierce the armor of the German tanks of 1940 (and a good deal in 1941). It earned the healthy respect from the German tank crews in 1940. Shoehorning the HE shell from the 25mm AA gun should not be that hard.

A towed version of the gun installed on the Char B1 would've been interesting until well into ww2. Put the muzzle brake on, a light carriage, and let the shells and shots fly, while being well under 1000 kg, and possibly under 800 kg.

The AT guns needed to be able to be moved by men (crew) at least for short distances and 1000-1500kg guns need very favorable circumstances for that to be possible.

If the AT gun is in the 1000-1500 kg range, this is already the territory of the better 75mm guns.

France had several facilities capable of making all sizes of cannon. Perhaps duplication of effort but in theory they could select the best gun or combine features (with enough time), and not have to settle on one answer.

There was no need to reinvent the wheel, especially once Navy gifted them the 47mm guns. Improve on these, modernize the 75s (a split carriage also means greater range), add some decent AP ammo and you're good wrt. the anti-tank means. A modern 47mm can be under 500 kg, while still being useful. Bigger guns can also do well when firing the HE and other ammo types, the small guns less well.

 

[Shortround6]

I'm glad that you find the not-so-powerful 47mm guns at your liking after all these years

Different times and different uses. What you need/want in a gun that needs to moved by men in 1937-40 France is not the same as what is needed in North Africa in 1941-42 and especially what is needed in a 20+ ton tank.

Shoehorning the HE shell from the 25mm AA gun should not be that hard.

Very true but but a 250g HE shell (give or take) makes a 610g HE shell (German 37mm AT gun shell) look like a power house destroyer of stone buildings and pillboxes/bunkers

A towed version of the gun installed on the Char B1 would've been interesting until well into ww2. Put the muzzle brake on, a light carriage, and let the shells and shots fly, while being well under 1000 kg, and possibly under 800 kg.

Which gun? the 75mm bomb thrower or the 47mm?

If the AT gun is in the 1000-1500 kg range, this is already the territory of the better 75mm guns.

Soviets are in a class of their own. Just about everybody else was pushing past 1500kg with not so good 75mm guns. The French 75 was just over 1500kg for a gun that should not be towed by motor vehicles, had very limited traverse and limited elevation which limited range.
The US did several conversions during the late 20s, the early 30s and in 1940-41. Depending on conversion the weight increase went from around 160kg to 335kg. The heavier one had a rather extravagant over 80 degrees of traverse and the need for 45-45 degrees of elevation is also subject to question. Some of the US conversions also involved new barrels and/or new recoil systems and some used modified/new breech mechanisms.
How much money do you want to spend?

 

[tomo pauk]

Different times and different uses. What you need/want in a gun that needs to moved by men in 1937-40 France is not the same as what is needed in North Africa in 1941-42 and especially what is needed in a 20+ ton tank.

I was alluding to the British Army taking the advantage of the 47mm guns that feature nowhere in the RN plans past the 1920s.

Very true but but a 250g HE shell (give or take) makes a 610g HE shell (German 37mm AT gun shell) look like a power house destroyer of stone buildings and pillboxes/bunkers

Just imagine the 6kg shell from a 75mm...

Which gun? the 75mm bomb thrower or the 47mm?

75mm bomb thrower?

Some of the US conversions also involved new barrels and/or new recoil systems and some used modified/new breech mechanisms.
How much money do you want to spend?

That will depend on a country and on the inventory of the older guns available.

 

[Elan Vital]

Tungsten, even for tool steel (around 7% alloy in the steel?) or for tungsten carbide cutting tools was not common, despite known advantages for cutting tools due to cost/supply.
Firing large lumps of it out of cannon barrels is a pretty expensive use. Germany was getting a decent percentage of it's Tungsten form Portugal. French access may have been better?
The Famous US 76mm APCR shot of 1944 was usually issued at rate of 2-4 rounds per tank by the "book". Some tanks didn't see any for a few weeks at a time but if they didn't see a Tiger or Panther for those days/weeks I guess it didn't make any difference.

France restarted mining of tungsten in 1939 (284 tonnes) after abandonning it in 1921 (much mining happened in WW1), but the invasion of 1940 prevented its growth, which instead happened postwar (500 to 900 tonnes a year) and especially during the Korean war. French Indochina was the main colonial supplier (553 tonnes in 1938), otherwwise France received tungtsen from the usual foreign suppliers, that is the Iberian Peninsula, North America and China (an agreement for over 6000 tonnes had been made in June 1940 but the Armistice cancelled everything).

The real unsung hero was Canada, which extracted so much tungsten ore in WW2 that the US told them to stop in 1943 as ore supply far outstripped refining capacity. It is only postwar that industrial capacity could supply a lot of tungsten carbide cores for HVAP and APDS. The Anglo-Canadians built more such ammo in WW2 than the US, which focused on tungsten for tooling.

A steel cored projectile fired from a Fench 75mm gun or it's equivalent still offers the increase of muzzle velocity and increased chance to hit a moving tank. With 900 m/s give or take MV (and obviously ever lower at 200-300-500-700m distances), it should be still under the velocity threshold for steel to shatter. Experiment with the idea and execution; if the shatter is still there, move to a bit heavier projectile to decrease the MV a bit. Experiment with tungsten tip and hardened steel shaft if/when there is enough of tungsten to be had.

A mid-power 75mm, that we have in hundreds or in thousands, beats the cr@p of the high-power 57mm gun that we don't have - most of the armies were reasonably well equipped with such 75/76mm guns already in the 1920s and 30s, but nobody have had the high-power 57mm guns. Most armies didn't even have the high-power 47 or 50 mm guns.

It's clear that even the superior performance of tungsten carbide doesn't invalidate the merit of steel cores as long as long as your gun didn't achieve 900-1000 m/s with full-bore ammunition. In the case of Brandt 75mm, you're talking about a 53mm core at 966 m/s, making it possibly more powerful than 6 pounder full-bore ammo. Even when using a 640 or 700 m/s class 75, you could still go with a slightly heavier core (say 60mm) to stay around 1000 m/s. The advantage of subcaliber ammo is that going for lighter but faster rounds can yield performance increases without exceeding the limit of your recoil system, as momentum can be reduced or kept constant.

True, but most armies of the 1930s didn't have enough guns to equip the field artillery units that they wanted.
A lot of the left over WW I guns were not in good shape and many were scrapped in the years following the war with armies keeping the guns/carriages that were in the best condition.
Training used up some guns and different economic problems delayed or canceled improvement/refurbishment plans. US did better than others as far as mounting old guns on new carriage's. France planned to but didn't get very far. France also had a real problem with their artillery program. It took way too long for them to decide that the French 75 was NOT the "be all and end all" to the artillery question and that some 105mm howitzers might actually be a good idea to have in the army. Production of several hundred 105mm howitzers sucked up a fair amount of the French artillery budget in the mid/late 30s. In typical French fashion of the time production was both slow and split between two different designs.
View attachment 857289
In 1934 the French apparently believed that trucks were passing fad.

This is actually sorta the period when more mobile carriages for high-speed traction start development. That said this just means that traditional carriages were ok for 30kph while the new carriages would be good for 50-70 kph. For war mobilization, the French settled on the 105mm Mle 1935 by Bourges rather than the Schneider design, the latter was not produced that much.
Mass motorization was also very much a late-war thing. The BEF was massively motorized because it only was some 15 divisions, about the number that the French and Germans managed to motorize in 1940. Having few high-speed traction guns is not as bad when most of your army is still horse-mobile.

A towed version of the gun installed on the Char B1 would've been interesting until well into ww2. Put the muzzle brake on, a light carriage, and let the shells and shots fly, while being well under 1000 kg, and possibly under 800 kg.

France already prototyped low-velocity 75mm howitzers in the 20s and 30s so little need for using the B1's gun here, if the concept had been retained.

There was no need to reinvent the wheel, especially once Navy gifted them the 47mm guns. Improve on these, modernize the 75s (a split carriage also means greater range), add some decent AP ammo and you're good wrt. the anti-tank means. A modern 47mm can be under 500 kg, while still being useful. Bigger guns can also do well when firing the HE and other ammo types, the small guns less well.

This is how they obtained the 37 and 47 casemate and then AT guns. The 37 used the Mle 1925 AA gun as a base, while the 47 used slightly modified Mle 1902 cases in new guns (esp barrels) to handle increased velocity that was more in line with the gun and case dimensions.

 

[Shortround6]

I was alluding to the British Army taking the advantage of the 47mm guns that feature nowhere in the RN plans past the 1920s.

The British 47mm guns in the 1920s were pretty much 1880s guns that had the black powder propelling charges replaces by smokeless powder without change the ballistics much. They might have produced some new barrels but kept the old ballistics.
As you well know I like the British 2pdr AT gun.................as a gun..........................I have serious problems with the mounts (both tank and towed) and the projectiles chosen used.
Problems with any successful use of a 47mm (3pdr) gun in British service requires NOT using the mounts (tank and towed) and projectile types that the 2pdr was stuck with.

Just imagine the 6kg shell from a 75mm...

Just imagine 6-8 men on foot (or with 1-2 horses) trying to cart around a worthwhile number of 75mm HE projectiles.

Cart being a rather accurate description here. Although this "cart" seems to have some seating for the crew?
AT guns were a conflicting series of requirements.
Cheap so they had enough of them.
Small so they were easy to move and hide.

Powerful enough to take out the enemy tanks fairly easily.
Suitable for secondary roles, like infantry support, which meant increase ammo supply and more transport capability, which added to cost, both money and man power.

75mm bomb thrower?

The 75mm in the hull of the Char B. It was only an AT gun because the German tanks used such thin armor.............and got really close to the French.