Alternative light and anti-tank guns, 1935-45

[Shortround6]

Advantage the British have vs. any Axis power is that the former don't need to skimp on tungsten.

Actually they did, They could not replace full bore AP of any type one for one with cored shot. They could carry more per tank than the Germans could but that is not saying much because in 1943/44 many German tanks didn't have any.
The US made a decision to prioritize tungsten cored shot for the 76mm/3in guns vs the 75mm gun armed Sherman's. Not saying the US didn't make any cored shot for the Sherman, but not much got issued. There were times in late 1944 when even the 76mm armed Shermans only had 2-4 rounds per tank (and sometimes none).
Germans had pretty much run out well before then.

Looking at the Soviet and US/French really medium-velocity 76-75mm guns, they all gained the improved penetration when the 'cored' ammo was used. The HVAP ammo offered more than 50% better AP performance than the APC ammo on the US gun. The Soviet 'arrowhead' projectile was better AP perfromer than the initial BR-350A ammo by some 10-20%.
We can also take a look at the Kwk 38, a.k.a. the short 5cm gun, used on a number of the Pz-IIIs in 1941 and 42. It started out with a lower velocity shot (under 700 m/s), that improved greatly with the APCR shot. Penetration between 1000m and 100m distance went up by the 20 to 70% interval (= greater increase closer to the gun).
The Kwk/StuK 40 L43 was also no great shakes wrt. the muzzle vlocity (full-weight projectile at 740 m/s, vs. ~720 for the 10cwt), and still the APCR brought the similar %-age jump in AP abilities as it was doing with the Kwk 38.

All of these do offer better results with the cored shot. Now how do you use your cored shot?
For the US, (and Cromwells?) do you use the cored shot in the 75mm guns when you can use 'normal shot' (APC=APCBC) to blow through the side of a Panther at 1500yds? Or a MK IV at 2000yds? and on the flip side you have to get well under 500yds to have a sporting chance of going through the lower bow plate of a Panther using the cored shot and no chance of going through the upper bow plate. At least the 76/3in gunned vehicles have a chance against the front of a Panther or Tiger at further than ramming distance.
At one point the Germans restricted the manufacture of cored ammo with a few exceptions. One was the ammo for the PAK 38 5cm gun. There were a lot more of them AND the PAK 38 (and MK III's with the 50mm gun) actually had a chance of taking out out Soviet tanks a greater than had grenade distance. The 50mm/L60 had around 300-500m more effective distance.

Now if we get back to basics for our hypothetical AT guns and we recognize that the requirements may have shift considerably for each year we can look to a basic formula for armor penetration that dates back to iron cannon balls VS rolled Iron plate. It gets updated with new constants for different armor materials and new projectile materials.

After all is said and done, with equal armor and equal projectiles it ussually comes down to how much force (Joules?) you can apply to every sq cm of target area (area of the circle equal to the Diameter of the shot/shell). Usually they use Muzzle velocity but if you know the speed at a given distance and can calculate the Joules of energy it should work (be close)
Now I have take the liberty of using an online calculator to figure out some common circles and come up with their areas in sq cm
20mm=3.14
25mm=4.9
37mm=10.752
40mm=12.566
47mm=17.35
50mm=19.635
57mm=25.52
75mm=44.18

Now if we know the Joules of muzzle energy we can make a good guess at to the relative performance of different rounds (assumes equal steel/heat treatment).
Helps explain the British 2pdr.
French 25mm.........................= 147,000
French 37mm S.....................= 37,000
French 37mm API.................= 70,200*
German 37mm AT................= 200,000
American 37mm...................= 340,000
British 2pdr.............................= 392,000
Soviet 45mm..........................= 404,000
German short 50mm...........= 566,000
German long 50mm............= 718,000 (?)
British 6pdr 10cwt................= 731,000
British 6pdr 7cwt...................= 989,00
Figures are from a book by Anthony Williams, The *French 37mm is a sabot round (steel and not Tungsten and the amount of force exerted by the core is unknown.
Figure for the German long 50mm is questionable as the projectile weights given by Williams do not match older books which makes the calculation off.
The rest of these should be for normal AP shot. Sometimes APCR (arrow head) shot comes out with a lower amount of Joules and sometimes higher but since we don't know the weight of the core or it's diameter trying the use the formula turns into total guess work.
Actual shape of shell (blunt vs pointy) can significantly affect down range performance, large shells of the same shape retain velocity better.

For the 2pdr vs 6pdr 10cwt argument. The 2pdr has 31,195 Joules per sq cm. The 6pdr 10cwt gun has 28,644 Joules/sq/cm. 92% rounded off.
The 6pdr 10cwt is for HE ammo (it never had AP) and with decent shell shape it may catch or exceed the 2pdr at distance. But the cost is very much greater weight and when the "standard" tank of the time was sporting 15mm armor it looked like the 2pdr could handle the job.

 

[tomo pauk]

All of these do offer better results with the cored shot. Now how do you use your cored shot?
For the US, (and Cromwells?) do you use the cored shot in the 75mm guns when you can use 'normal shot' (APC=APCBC) to blow through the side of a Panther at 1500yds? Or a MK IV at 2000yds? and on the flip side you have to get well under 500yds to have a sporting chance of going through the lower bow plate of a Panther using the cored shot and no chance of going through the upper bow plate. At least the 76/3in gunned vehicles have a chance against the front of a Panther or Tiger at further than ramming distance.

I have no illusions that the cored shot will supplant the other shots by a flick of the switch. Even by having 5-6 per a tank ups the game with many hundreds of tanks in operations daily.
Same as the Americans and the Germans, the British will also need to start outfitting the tanks and AFVs with a powerful 3in class gun by sid/late 1942, ie. an equivalent of the 75 or 77mm HV/Kwk 40/US 3in/76mm.
By early 1944, most of the frontline tank units using the Shermans and Churchills, earmarked for the D day, should've had such a gun in the turret. Plus whatever can be spared for Italy. By what time the best AP shot for them is either APDS or, much less likely, the APCR (never much loved by the British), with APCBC being the next best thing.

Now if we know the Joules of muzzle energy we can make a good guess at to the relative performance of different rounds (assumes equal steel/heat treatment).
Helps explain the British 2pdr.

Thank you for the effort to sift through the numbers and doing the math.
Trick was that absolute performance counted (and still is). So we have the long 5cm punching through 59mm at 500m with the MV of 835 m/s, and the 2pdr managing 51mm with 853 m/s at ~450 m (2800 ft/s). Even the short 5cm can compete with 47mm at 500m, despite the math being so bad for it with 685 m/s (or, in the E/S values, 28826 J/sq cm - same as the 6 pdr 10 cwt).
(all for 30 deg from vertical; all for 'full weight' AP shot/shell)

We know that a tank that is pierced with a 3 kg shot will be in a much worse shape than the one that is pierced by a 1 kg shot; ditto for the crew. We also know that, as a tank gun that should be using more HE ammo than the AP ammo, the 6pdr is superior.

The 6pdr 10cwt is for HE ammo (it never had AP) and with decent shell shape it may catch or exceed the 2pdr at distance. But the cost is very much greater weight and when the "standard" tank of the time was sporting 15mm armor it looked like the 2pdr could handle the job.

The tanks British were exporting were indeed weakly armored. French tanks, OTOH, were very well armored, and so was in the plans for a good number of the future British tanks. Planing for how to counter the well-armored enemy tanks (be that German or perhaps French - the jury was still out in the 1930s) on a short notice and within the budget would've been good.
Assumption that a good AT gun immediately makes a good tank gun was also off by a good margin. Same with the assumption that a tank is best off without the HE shell (that included the interwar 3 pdr, the 2 pdr; also the 6 pdr until half of the war passed). CS tanks nevertheless.

 

[marathag]

The coast defense 6pdr 10cwt that you linked to is just that, a 1060lb barrel

For initial piece. If the goal is to make that more mobile, things can go lighter, like from the US M3 75mm tube went from 893 pounds for the lightweight M6 of 410 pounds

The intermediate T13E1/M5 for aircraft use was even slightly lighter, but it didn't have the 4000 round barrel life of the M3, either. Never have been able to track down the weight of the tube itself for that one.

Perfect is the enemy of good enough.

The M5 with a concentric recoil setup instead of a separate buffer and recuperator hydraulic cylinders like 'real' Artillery pieces had.
It's compact, and light weight.

Put a big ass muzzle brake on it, and a sensible light carriage, it's a good general purpose Infantry/AT gun

It would be lighter than the M1 57mm, as the tube on that was 727 pounds, and has a wide variety of ammo to fire, unlike the later 57mm/6pdr

 

[Shortround6]

I have no illusions that the cored shot will supplant the other shots by a flick of the switch. Even by having 5-6 per a tank ups the game with many hundreds of tanks in operations daily.
Same as the Americans and the Germans, the British will also need to start outfitting the tanks and AFVs with a powerful 3in class gun by sid/late 1942, ie. an equivalent of the 75 or 77mm HV/Kwk 40/US 3in/76mm.
By early 1944, most of the frontline tank units using the Shermans and Churchills, earmarked for the D day, should've had such a gun in the turret. Plus whatever can be spared for Italy. By what time the best AP shot for them is either APDS or, much less likely, the APCR (never much loved by the British), with APCBC being the next best thing.

Well, we are trying to cover 10 years and yes, just about everybody that lasted went through at least 3 AT guns, went through 4 or 5. Only the British managed to bring APDS into somewhat wide spread service (2 guns/ types of ammo) and the jury is bit undecided on the success of the 2nd one during WWII or at least for a few months.
The British need for a powerful tank is undisputed. But it doesn't matter how good your AT gun is if you don't build a big enough tank to hold it. British tank design/history is the subject for about 6-12 more threads

Trick was that absolute performance counted (and still is). So we have the long 5cm punching through 59mm at 500m with the MV of 835 m/s, and the 2pdr managing 51mm with 853 m/s at ~450 m (2800 ft/s). Even the short 5cm can compete with 47mm at 500m, despite the math being so bad for it with 685 m/s (or, in the E/S values, 28826 J/sq cm - same as the 6 pdr 10 cwt).
(all for 30 deg from vertical; all for 'full weight' AP shot/shell)

We know that a tank that is pierced with a 3 kg shot will be in a much worse shape than the one that is pierced by a 1 kg shot; ditto for the crew. We also know that, as a tank gun that should be using more HE ammo than the AP ammo, the 6pdr is superior.

Not arguing with that. What I argue with is that the 2pr was considered trash by some and was little better than most peoples 37mm guns. The 2pdr was not the solution for the 1942-43 battles. But it could have done a lot better in 1939-40-41 with better ammo and sight (in tanks) and would have given a better account of itself in the Pacific up until 1945.
The Germans had started with plain AP (not capped) in the 37mm, the short 50mm and the long 50mm. They went to at least capped in both the 50mm guns and sources say APCBC for at least the short 50mm. They didn't wait for end of 1942 to do it. The 2pdr as a hole puncher could have been very close to the short 50mm gun given better ammo (capped) and better sights/doctrine. The British made almost 10 times the amount of HE ammo for the 6pdr than they did for the 2pdr in 1942. That was built in the factories not issued in units in the field.
German 37mm HE held 25 grams, British 2pdr held 62-64 grams, German 50mm held about 165 grams. British 6pdr could have held about 225 grams? The next jump is to 75mm and they seem to start at around 400 grams and go up? US 76mm held the 390-400 grams and was disliked for it. Which left the Germans in France, NA and early Russia where?
Take a look at the 2pdr figures again and consider that the 25pdr using a 20lb shot at 2000fps (supercharge plus increment and muzzle brake) was good for 70mm penetration at 400yds at 0 degrees impact. 54 mm at 500yds at 30 degrees starts sounding a whole lot better than trying to use 25pdrs as AT guns.
But yes, the 6pdr should have been in production and being issued over the winter of 1940/41 in ideal conditions.

The tanks British were exporting were indeed weakly armored. French tanks, OTOH, were very well armored, and so was in the plans for a good number of the future British tanks. Planing for how to counter the well-armored enemy tanks (be that German or perhaps French - the jury was still out in the 1930s) on a short notice and within the budget would've been good.
Assumption that a good AT gun immediately makes a good tank gun was also off by a good margin. Same with the assumption that a tank is best off without the HE shell (that included the interwar 3 pdr, the 2 pdr; also the 6 pdr until half of the war passed). CS tanks nevertheless.

Again, British tank doctrine/theory/fevered dreams may be left for other threads, there is no doubt in my mind that they were lost in wilds on this.

But some this is a doctrine issue that is somewhat easy to solve.
1. Decide that your existing AT guns and tank guns need HE of some sort.
2. Issue HE ammo to existing guns.
3. Decide what you want the next generation of armored warfare (attack and defense) to do and design/build that generation of guns accordingly. Don't wait for the new guns before you design/build HE ammo.

I will note that the British were approving the 2pdr gun at about the same time (granted there were long development times and tooling up times before deliveries) that the French were testing/ordering their new tanks and orders were placed before testing was completed. French may not have been sending over plans for the French new tanks on the Dover Ferry with constant updates? The 2pdr could certainly stop any German tank in 1938-39, or Italian (OK they were in danger from .5in Vickers guns) or Soviet or Japanese or American (assuming you can find an American tank in 1938) and as shown the 2pdr was not quite the door knocker the German 37mm was. German 37mm had 18,600 Joules/sq/cm.
Not saying they are one shot killers but any French tanks that thinks they can survive 20-40 hits and keep fighting might be surprised.

 

[Shortround6]

It would be lighter than the M1 57mm, as the tube on that was 727 pounds, and has a wide variety of ammo to fire, unlike the 57mm/6pdr

Granted a 6pdr smoke shell would be near useless but the narrow availably of shells was also doctrine driven and for some reason the Americans may have developed an HE round but it was never given a name/nomenclature or was standardized let alone produced. American units in NW Europe may have been issued with British HE shells?

AT gunners are of two minds about muzzle brakes.
They allow for lighter guns with greater power.
They screw up your camouflage and make you easier to spot and they make it hard to see where your shells are landing.

 

[z42]

Looking at the Soviet and US/French really medium-velocity 76-75mm guns, they all gained the improved penetration when the 'cored' ammo was used. The HVAP ammo offered more than 50% better AP performance than the APC ammo on the US gun. The Soviet 'arrowhead' projectile was better AP perfromer than the initial BR-350A ammo by some 10-20%.
We can also take a look at the Kwk 38, a.k.a. the short 5cm gun, used on a number of the Pz-IIIs in 1941 and 42. It started out with a lower velocity shot (under 700 m/s), that improved greatly with the APCR shot. Penetration between 1000m and 100m distance went up by the 20 to 70% interval (= greater increase closer to the gun).
The Kwk/StuK 40 L43 was also no great shakes wrt. the muzzle vlocity (full-weight projectile at 740 m/s, vs. ~720 for the 10cwt), and still the APCR brought the similar %-age jump in AP abilities as it was doing with the Kwk 38.

Advantage the British have vs. any Axis power is that the former don't need to skimp on tungsten.

The Germans would have to invent APFSDS then, to compensate for lack of tungsten.

Even using only hardened steel and using non-heroic MV to avoid shattering the (capped) dart, thus using mostly the increased sectional density, should be able to get pretty decent results. A 75mm smoothbore firing steel APFSDS at, say, 1000 m/s should be plenty for any WWII era tank at realistic ranges?

 

[tomo pauk]

he British need for a powerful tank is undisputed. But it doesn't matter how good your AT tank gun is if you don't build a big enough tank to hold it. British tank design/history is the subject for about 6-12 more threads

(my edit)
British tank realities and what-ifs deserve a web site just for them
Valentine and Churchill tanks were big enough to carry even the high-power 57mm and the mid-power 75mm (granted, via some/a lot of sacrifices in the case of the Valentine). Matilda have had a turret with a 6pdr mounted for trials (the trials maybe never happened?); also the Soviets seem to up-gunned one with the 76mm gun of their own, via application of the external mantlet. So there is a lot of real estate available for the substantial guns on the British tanks.
Similar thing was with the cruiser tanks.

A reason why I'm favoring the Kwk 40 and the 77mm HV lookalike vs. the 17prd is that it should be much easier to install on the Shermans and Churchills, while with still a lot of AP capability.

Not arguing with that. What I argue with is that the 2pr was considered trash by some and was little better than most peoples 37mm guns. The 2pdr was not the solution for the 1942-43 battles. But it could have done a lot better in 1939-40-41 with better ammo and sight (in tanks) and would have given a better account of itself in the Pacific up until 1945.

I've never said that the 2pdr had problems in killing the Axis tanks in 1940.
It is it's other shortcomings that were not necessary, yet were a handbrake for the needs of the British Army. As a tank gun, it was a wrong choice since, even if outfitted with a passable HE shell, it was well behind the curve. As an 'light' anti-tank gun, it was too heavy and too complicated for what it was offering.

German 37mm HE held 25 grams, British 2pdr held 62-64 grams, German 50mm held about 165 grams. British 6pdr could have held about 225 grams? The next jump is to 75mm and they seem to start at around 400 grams and go up? US 76mm held the 390-400 grams and was disliked for it. Which left the Germans in France, NA and early Russia where?

That left Germans in a much better position.
German field and Flak artillery have had direct sights, so they were very usable as the anti-tank guns when/if the need arises. See not just Arrass or when a KV was encountered, but also how the Germans dealt with the field fortifications and block houses.
German tanks and AFVs were also outfitted with decent HE throwers already in 1939 (that were still good at taking out the same tanks that 37mm was killing), a thing that British lacked until the M3 medium was acquired in 1942. Germans were also employing the Czech 47mm guns, both in towed and self-propelled version (the later already in 1940).

Take a look at the 2pdr figures again and consider that the 25pdr using a 20lb shot at 2000fps (supercharge plus increment and muzzle brake) was good for 70mm penetration at 400yds at 0 degrees impact. 54 mm at 500yds at 30 degrees starts sounding a whole lot better than trying to use 25pdrs as AT guns.
But yes, the 6pdr should have been in production and being issued over the winter of 1940/41 in ideal conditions.

If the 6pdr 10cwt is chosen for Army production by 1936, that gun should've been on the British tanks and in the AT units already in 1939. By then, start making a better ammo for it, as well as a next-gen AT gun.
There was no obstacle for the field pieces, like the 18 and 25 pdr, to be outfitted with AT accessories (direct sight against the moving targets, a half-decent anti-armor shot/shell) well before ww2. Perhaps it was not specified by the doctrine? No doctrine = no hardware...

But some this is a doctrine issue that is somewhat easy to solve.
1. Decide that your existing AT guns and tank guns need HE of some sort.
2. Issue HE ammo to existing guns.
3. Decide what you want the next generation of armored warfare (attack and defense) to do and design/build that generation of guns accordingly. Don't wait for the new guns before you design/build HE ammo.

Agreed.
The doctrine that tank guns need HE shells seems to fell out of favor come late 1920s/early 1930s, to re-emerge in 1942 for the British?

 

[tomo pauk]

For initial piece. If the goal is to make that more mobile, things can go lighter, like from the US M3 75mm tube went from 893 pounds for the lightweight M6 of 410 pounds

Put a big ass muzzle brake on it, and a sensible light carriage, it's a good general purpose Infantry/AT gun

It would be lighter than the M1 57mm, as the tube on that was 727 pounds, and has a wide variety of ammo to fire, unlike the later 57mm/6pdr

If the 1000 kg/2200 lb is the upper limit, the modern ( = not the ww1 leftover) 75/75mm guns certainly have their appeal.

The Germans would have to invent APFSDS then, to compensate for lack of tungsten.

Even using only hardened steel and using non-heroic MV to avoid shattering the (capped) dart, thus using mostly the increased sectional density, should be able to get pretty decent results. A 75mm smoothbore firing steel APFSDS at, say, 1000 m/s should be plenty for any WWII era tank at realistic ranges?

Going with a smooth-bore gun would've alleviated a few problems. The 1st will be that the barrel should have a longer life, since there is no rifling to 'wrestle' with the high pressure and temperature.
(when testing the under-caliber saboted HE shell for the 15cm howitzer, in order to gain MV and range, the much increased barrel wear was a noted )
Fin-stabilized HE and HEAT shells were a known thing well before ww2, so that solves the issue of how multi-purpose the gun is. Barrels should be also faster and cheaper to make.

The APCR-like shot that has a hardened steel core instead of tungsten can also work.

 

[z42]

Going with a smooth-bore gun would've alleviated a few problems. The 1st will be that the barrel should have a longer life, since there is no rifling to 'wrestle' with the high pressure and temperature.
(when testing the under-caliber saboted HE shell for the 15cm howitzer, in order to gain MV and range, the much increased barrel wear was a noted )
Fin-stabilized HE and HEAT shells were a known thing well before ww2, so that solves the issue of how multi-purpose the gun is. Barrels should be also faster and cheaper to make.

Cheaper barrels that are less sensitive to wear would be one advantage, but another, arguably even bigger one, is that it allows much longer projectiles. Spin-stabilized projectiles are in practice limited to a length/diameter ratio of 6 or thereabouts (spinning faster helps, but that has limits too), go too high and the projectile starts to tumble in the air. A fin-stabilized projectile is limited essentially only by your metallurgy, don't want to have the dart tie itself into a pretzel once it hits something. Thus you could get pretty good sectional density without having to go to exotic heavy materials like tungsten or uranium.

In general, I think subcaliber fin-stabilized saboted projectiles were an area that could have been developed to a usable state in the run-up to WWII. No walk in the park, of course, but starting in the mid-1930's and you could have had something pretty decent in service during WWII? Not only for armor penetration, but also for long-range artillery and heavy AA (as mentioned in that other recent thread of yours: AA guns + rockets alternatives for 1935-45 ).

The APCR-like shot that has a hardened steel core instead of tungsten can also work.

I think it was mentioned (perhaps even in this very thread?) that the Germans experimented with such, and the results were in the same ballpark as the traditional APCBC.

 

[Elan Vital]

Cheaper barrels that are less sensitive to wear would be one advantage, but another, arguably even bigger one, is that it allows much longer projectiles. Spin-stabilized projectiles are in practice limited to a length/diameter ratio of 6 or thereabouts (spinning faster helps, but that has limits too), go too high and the projectile starts to tumble in the air. A fin-stabilized projectile is limited essentially only by your metallurgy, don't want to have the dart tie itself into a pretzel once it hits something. Thus you could get pretty good sectional density without having to go to exotic heavy materials like tungsten or uranium.

In general, I think subcaliber fin-stabilized saboted projectiles were an area that could have been developed to a usable state in the run-up to WWII. No walk in the park, of course, but starting in the mid-1930's and you could have had something pretty decent in service during WWII? Not only for armor penetration, but also for long-range artillery and heavy AA (as mentioned in that other recent thread of yours: AA guns + rockets alternatives for 1935-45 ).



I think it was mentioned (perhaps even in this very thread?) that the Germans experimented with such, and the results were in the same ballpark as the traditional APCBC.

As shown by the postwar Soviets (and 50's American attemps), APFSDS can also massively enhance the performance of even plain tungsten carbide cores over APDS. The Soviets obtained excellent perforation of lightly angled plates using the plain old 45mm APCR core, which was a fraction of the weight of a 105 or 120mm APDS of the day. A great way to do more with limited quantities of tungsten if you cannot just use steel rods.

---

As to French progression/practice for tank/dedicated AT guns (75mm DP field gun excluded) in the 30s:
- 25 mm is the culmination of developments of small caliber AT guns since 1918, with APCBC type bullet.

- 37 mm AC 34 casemate gun is based on the model 1925 naval AA gun with afaik minimal modifications to the case or charge, but a new barrel and dedicated AP ammo (APBC at least) and was just a more compact alternative to the 47mm AC34 as Maginot line casemates were not originally tailor-made for these guns.

- 47mm AC 34 is based on the Hotchkiss mle.1902 naval gun, but the case was modified and is not backwards compatible with the former gun, the barrel and possibly the rest of the gun is new, ammo is new (APBC at least). Increased velocity from nearly 700 m/s on the mle.1902 to 855/880 m/s on the AC34.
AC34 with a sliding breech was designed for experimental tank turrets in 1937.

- 47mm SA37 reuses the same ballistics and case as AC 34 but with a lighter barrel, as the casemate gun barrels were deliberately quite thick to make them more resistant against enemy fire.

- 47mm SA34 is an adapted 47mm mle.1892 naval gun reused as a stopgap with old naval APHE, a successor started development almost as soon as it existed
- 47mm SA35 is a brand new tank gun with APC projectiles and a heavily necked case to reduce total length in a tank.
- 37mm SA38 is brand new tank gun with APC projectiles and a heavily necked case to reduce total length in a tank.

- 75mm tank/self-propelled gun: sliding breech derivative of the 75mm mle.1929 casemate gun, same ballistics as full length mle 97 (570 m/s), retains the thick casemate type barrel. Always provided with a spring-based powered rammer with automatic closing of the breech when the rammer recoils back to further facilitate loading (especially at different elevations of the gun). Developped in 1937 (if not even before) for experimental self-propelled guns, fortification assault tank hull mounts and 2/3-man tank turrets

- 75mm fortification assault tank gun: same as above but used at 640 m/s muzzle velocity. Used in early forms of the fortification assault tank.
75mm guns had old APHE but were testing various modern APC/APCBC projectiles.

- 105mm mle.1913 gun (550 m/s MV) used with minimal modifications in fortification assault tanks.
- 90 mm CA 39 AA gun (820 m/s) or same but shortened by 1m (700 m/s) used with minimal modifications in fortification assault tanks.
Neither of these two guns were modified to use shorter necked ammunition and shorter recoil lengths, so the turrets using them had to be bulkier and heavier than was possible.

All 37 and 47mm tank guns (including the short SA18) were provided with HE ammunition in spite of their weakness. 37mm HE had over 50 grams of payload.
Casemate 37 and 47mm guns (and SA37 antitank) didn't start with HE but this was added/to be added in 1940 (admittedly, this was a less urgent matter considering Maginot line fortifications had plenty of HE and machineguns).

 

[tomo pauk]

- 75mm tank/self-propelled gun: sliding breech derivative of the 75mm mle.1929 casemate gun, same ballistics as full length mle 97 (570 m/s), retains the thick casemate type barrel. Always provided with a spring-based powered rammer with automatic closing of the breech when the rammer recoils back to further facilitate loading (especially at different elevations of the gun). Developped in 1937 (if not even before) for experimental self-propelled guns, fortification assault tank hull mounts and 2/3-man tank turrets

- 75mm fortification assault tank gun: same as above but used at 640 m/s muzzle velocity. Used in early forms of the fortification assault tank.
75mm guns had old APHE but were testing various modern APC/APCBC projectiles.

Were these two also experimental types?

 

[Shortround6]

British tank realities and what-ifs deserve a web site just for them
Valentine and Churchill tanks were big enough to carry even the high-power 57mm and the mid-power 75mm (granted, via some/a lot of sacrifices in the case of the Valentine). Matilda have had a turret with a 6pdr mounted for trials (the trials maybe never happened?); also the Soviets seem to up-gunned one with the 76mm gun of their own, via application of the external mantlet. So there is a lot of real estate available for the substantial guns on the British tanks.
Similar thing was with the cruiser tanks.

We are getting sidetracked into the tanks
The Valentine was NOT big enough to carry the higher powered guns (bigger than 2pdr) successfully. Matilda is doubtful. Same thing with the Crusader III with the 6pdr.
Not saying they weren't built or used. But they were not very good tanks. The Early 6pdr Valentines were basically tank destroyers. They took out one man AND the co-ax machine gun to fit the 6pdr into place. Given the scarcity of 6pdr HE ammo even at the end of 1942 that means you have a 1 trick pony with a low rate of fire and dismal vison. They put the co-ox gun back on the later big gun versions but it had about 1/2 the ammo of the early versions (1575 rounds vs 3150 rounds) . Kind of the same with Crusader. Down to a two man turret crew, commander was now the loader. Since the Crusader had started with the stupid bow machine gun turret it still had a lot of room for MG ammo.

A reason why I'm favoring the Kwk 40 and the 77mm HV lookalike vs. the 17prd is that it should be much easier to install on the Shermans and Churchills, while with still a lot of AP capability.

Agreed, the 17pdr was too much of good thing until you get tanks into the mid 30 ton and up range.

I've never said that the 2pdr had problems in killing the Axis tanks in 1940.

I didn't say you did. If you had I would not have put in "some people".

It is it's other shortcomings that were not necessary, yet were a handbrake for the needs of the British Army. As a tank gun, it was a wrong choice since, even if outfitted with a passable HE shell, it was well behind the curve. As an 'light' anti-tank gun, it was too heavy and too complicated for what it was offering.

2pdr was being put into production tanks in mid 1937 (A9) and in quantity in 1939. The British had built a lot more 2pdr armed Cruisers by the end of the summer of 1939 than the Germans had built MK IIIs. Being selective here but the British had used it on all of the 4 types of earlier cruisers and the Matilda II. British may have more 2pdr armed tanks the Germans did Pz 35s, Pz 38s and MK IIIs, it would be fairly close.
I agree on the towed AT gun, but a version with a simple split trail carriage something like a Czech 47mm except for motor towing might have saved money and hundreds of pounds. Call it the 2pdr mountain gun to get it passed the treasury men (except they would probably say there no tanks in the mountains
Again, as hole puncher, the 2pdr was equal to or slightly better than the Soviet 45mm AT gun or any of the French 47mm tank guns. The French 47mm AT gun is somewhat different story but then you have a 1070kg gun with solid rubber tires and you are creeping close to the weight of 6pdr 7cwt.
We seem to get thinks like this on Wiki for the Belgian 47mm AT gun " In medium-range armor penetration, the Belgian model even outperformed the British Ordnance QF 2-pounder. For instance, armor-piercing rounds could penetrate 47 millimetres (1.9 in) of armored steel at a range of 300 metres (980 ft)." now maybe I am math challenged but the 2pdr with AP shot it credit with 47mm (the same) at 500 yds in the link provided, I am fairly certain that 500yds is a longer distance the 300 meters

That left Germans in a much better position.......................
German tanks and AFVs were also outfitted with decent HE throwers already in 1939 (that were still good at taking out the same tanks that 37mm was killing), a thing that British lacked until the M3 medium was acquired in 1942. Germans were also employing the Czech 47mm guns, both in towed and self-propelled version (the later already in 1940).

leaving out the flak and field artillery the Germans had their own vaunted towed 37mm door knockers, the towed (dragged?) Czech 47mm and in all of Germany in May 1940
382 Pz III, 143 Pz 35s, 238 Pz 38s (763 37nn armed tanks) and 290 Pz IV with the short 7.5cm guns. They had 1092 Pz IIs with 2cm guns with solid shot. Not all participated in the French campaign. German 3rd Panzer division started with 26 MK IV tanks out of 343 tanks total, German 4th Panzer division had started with 24 MK IVs out of 331 tanks total.
Point was and is, the Germans did have HE capability, But aside from the MK IVs the German tank ability to use HE was not much better than the British if they had provided HE shells for the 2pdr from the start.

If the 6pdr 10cwt is chosen for Army production by 1936, that gun should've been on the British tanks and in the AT units already in 1939. By then, start making a better ammo for it, as well as a next-gen AT gun.

How and why?
As shown earlier the 6pdr 10cwt has no significant AP capability over the 2pdr (if as good). This is theoretical as the 10cwt was never given AP shot. Not saying you can make 2pdr ammo at a 3 to one ratio over 6pdr ammo but the 2pdr has got to somewhat cheaper. So you are paying more money for a gun and for ammo that probably isn't as good punching holes in things, neither one can use smoke, the 10cwt HE isn't even close to anybody's 75mm/3in gun (maybe not even close to the British 3in close support howitzer?).
The 10cwt gun has problem, they used about a 72cu/in (?) chamber in it. The 7cwt gun used a 100cu.in chamber. You can't hot load the 10cwt gun and improve things much that way. Maybe you can rechamber the 10cwt guns for larger/later ammo? But high velocity (the 10cwt is sort of medium velocity for an AT gun) guns wear out barrels quickly.

There was no obstacle for the field pieces, like the 18 and 25 pdr, to be outfitted with AT accessories (direct sight against the moving targets, a half-decent anti-armor shot/shell) well before ww2. Perhaps it was not specified by the doctrine? No doctrine = no hardware...

Mostly agree, no doctrine means no sights, real problem.
The AP shot is a real problem.
For the 18pdrs it is a waste of effort, there simple were not that many left. Most of the modern ones (split trails and motor towable) had been converted to 18/25pdrs. Over 1000 conversions had been made.
There already was a MK 3T AP shot listed in the books, No idea how many were in stock. It was a solid shot (uncapped?) with tracer and used the standard propelling charge which probably means a MV of 1625fps/495ms. Not worth putting a piercing cap on. Save the engineering effort for a newer gun.
Main problem with the 25pdr is the lack of velocity. It took a "supercharge" to get the 25lb projectile up to 1700fps (518m/s)
With a standard charge (zone 3) the gun had MV of 1486fps/453ms and while you could have gone to the lighter 20lbs shot with charge I don't know where you wind up.
When they did go to the supercharge with 20lb shot the gun was unstable (bounced around on the wheels) and they had to develop the muzzle brake.
Now in 1938-41 the British were scrambling just to get enough 25pdrs into the field as is let alone trying to turn them into anti tank guns although they did go through quite a few experiments (the AP shot went through Mks 1t through 6t and 8t, mainly tracer changes) there was an capped version by Jan 1943 (way too late), there was an APCBC shell (HE content) before they gave up as the 25pdr didn't have the velocity to make it worthwhile (weight is not given) and the British did fool around with HEAT ammo from 1940 until after the war but but pretty much ended in late 1944. They learned a lot that could be applied to other projects. Basically the British did not know enough about the basic principles of the hollow charge phenomenon in 1940 and a lot of work needed to be done. This idea of just using HEAT shells in all sorts of guns in 1939-40-41 needs to be trashed. The first German 7.5cm shell used in the MK IV tank was good for about 70mm of penetration.

 

[Shortround6]

The idea of using either FSDS for any reason or even DS ammo for any reason needs a lot more than just the idea, it needs a lot of research and development.
It is real easy to fire the experimental round out of the muzzle and record a very high velocity. Problems start cropping up when you try to actually hit a target at a distance (or at artillery distances, even get most of the rounds into the same farmer's field). Now in the 1960s after a nearly a decade of supersonic manned flight and launching satellites into space and using high speed anti-aircraft rockets/missiles most nations had a lot more knowledge about what it took to keep long pointy things going straight at high speeds. Nobody has the knowledge in 1939. Germans spent how long trying to get their sabot's to discard without disrupting the flight of the main projectile? They also tried using malleable studs in the front and malleable skirt in the back. British had trouble with the 6pdr but got it solved. It took longer to solve the 17pdr problem/s. Americans tried in WW II, post war and the 1950s, stuck with HVAP because they couldn't get the sabots to give the accuracy they wanted.
Doesn't matter how much armor the projectile will go through if you can't even keep 1/2 the shots on a medium sized tank at 500-600yds.

It is a lot easier, an awful lot easier, to use the APCR idea. But that doesn't work so well with steel cores. It works at short ranges but it doesn't work at long ranges. The composite projectile doesn't have enough mass for it's frontal area and the ballistic coefficient is not good.
You also run into the problem of steel hitting steel at high velocity and around 3000fps/ 915ms is the threshold. This is impact velocity so even 3000fps guns work well once they are shooting past the first few hundred yds/meters. But heading for the upper 3000fps range can have your 'core' shattering on impact on armor that it could penetrate at several hundred yds further out. Having to swap ammo in and out of the gun depending on target range is a pain in the butt, and you need to have two/ three types of ammo in the tanks and after a short period in combat, you are likely to be out of the best round for the distance you want (need) to fire at.

 

[tomo pauk]

We are getting sidetracked into the tanks

We certainly do

I didn't say you did. If you had I would not have put in "some people".

Whoops Sorry.

How and why?
As shown earlier the 6pdr 10cwt has no significant AP capability over the 2pdr (if as good). This is theoretical as the 10cwt was never given AP shot. Not saying you can make 2pdr ammo at a 3 to one ratio over 6pdr ammo but the 2pdr has got to somewhat cheaper. So you are paying more money for a gun and for ammo that probably isn't as good punching holes in things, neither one can use smoke, the 10cwt HE isn't even close to anybody's 75mm/3in gun (maybe not even close to the British 3in close support howitzer?).

Start by 1937-38.
Take a look at the French shells for the 145/155/194mm artillery, there were the shells with ballistic caps available before ww2. Application of these on the AP ammo will make the loss of velocity happen at the lower rate, thus improving both chance to hit and penetration past 500 m, and especially at about 1000m. Check out the 37mm Mlle 1935 shot, the almost-APCR that added 50% to the MV vs. the old, full weight AP shot for the French 37mm gun; it also increased penetration in a major way. The AP ammo for the 25mm ATG can also give ideas to the people designing the improved AP ammo.

My point with the 10cwt is to have it instead of the 2pdr, not to compete with the 75mm stuff.

Main problem with the 25pdr is the lack of velocity. It took a "supercharge" to get the 25lb projectile up to 1700fps (518m/s)
With a standard charge (zone 3) the gun had MV of 1486fps/453ms and while you could have gone to the lighter 20lbs shot with charge I don't know where you wind up.

With the zone 3, the 20lb shot might perhaps go to 500 m/s?
We can take a look on the other guns with sedate MVs. The French hull-mounted 75mm howitzer was doing 470 m/s with an 14lb APHE Mlle 1910 (!!) shot, piercing 40mm at 30 deg at 400 m (can be translated). Kwk 37 was good for 39mm at at 30 deg at 500 m with the 15 lb APHE, under 400 m/s MV.
A decent 20 lb APHE on the 25pdr should be ofering perhaps 45mm at 30 deg at 500 m?

This idea of just using HEAT shells in all sorts of guns in 1939-40-41 needs to be trashed. The first German 7.5cm shell used in the MK IV tank was good for about 70mm of penetration.

HEAT was not a panacea.
BTW - these 70mm of penetration is still far better than what the Pz-IV was doing with non-HEAT ammo.

 

[yulzari]

There is talk of high velocities and talk of using medium artillery as anti tank guns but one thing that has not been mentioned is the chance of hitting something. At the large calibre slow velocity there is the British 3.7":CS gun that swapped with the 2 Pounder. A slow arching trajectory more akin to an 1850s rifle musket than a 1940s rifle. At the other extreme is the 2 Pounder with Littlejohn adaptor which threw a small hard object very fast.

In the first case not only do you have to have the range very precisely estimated or the round will fall short or fly over the target but also know where the target will be by the time the slow heavy object wanders it's leisurely way to the other end of it's flight.

Of course very high velocities risks the shot breaking up on contact but the faster the flight the flatter the trajectory so one can both gain far more tolerance in range estimation but also the target has far less time to move or change speed during the time of flight. Hence you have an excellent chance of hitting a moving target with a 2 Pounder with Littlejohn adaptor and a negligible one of hitting with. 3.7" CS gun.

 

[Shortround6]

For consideration

From left to right, the rounds are: 37x94R (French 37mm Mle 1916/1918), 37x149R (French 37mm Mle 1938), 37x249R (German 3,7cm), 37x257R (Polish wz 36 - 37mm Bofors), 37x268R (Czech 37mm vz 34/38), 40x304R (British 2pdr), 47x195R (Italian 47mm Mod 37 - Austrian Bohler), 47x193R French 47mm Mle 1935, 47x280R (Belgian AT).
Photo is 2nd hand but from Anthony Williams old website and the caption is from another website that answered a question on French tank and Anti-tank rounds.

 

[z42]

There is talk of high velocities and talk of using medium artillery as anti tank guns but one thing that has not been mentioned is the chance of hitting something. At the large calibre slow velocity there is the British 3.7":CS gun that swapped with the 2 Pounder. A slow arching trajectory more akin to an 1850s rifle musket than a 1940s rifle. At the other extreme is the 2 Pounder with Littlejohn adaptor which threw a small hard object very fast.

In the first case not only do you have to have the range very precisely estimated or the round will fall short or fly over the target but also know where the target will be by the time the slow heavy object wanders it's leisurely way to the other end of it's flight.

Of course very high velocities risks the shot breaking up on contact but the faster the flight the flatter the trajectory so one can both gain far more tolerance in range estimation but also the target has far less time to move or change speed during the time of flight. Hence you have an excellent chance of hitting a moving target with a 2 Pounder with Littlejohn adaptor and a negligible one of hitting with. 3.7" CS gun.

??? Are we reading the same thread? Seems to me the difficulty of hitting a target at uncertain range with a low MV weapon has been pointed out in about every other post?

 

[Shortround6]

The 3.7 CS gun was pretty much a smoke thrower. It shared nothing except the bore size with the 3.7 pack howitzer.
There was supposed to be an HE round for it.
Muzzle velocity was a closer match for an 1850 cavalry pistol than even a musket. about 620f/s(189m/s) for a 15lb shell/bomb. Max range was 2000yds but good luck hitting anything with on purpose. For lobbing smoke shells into an area for form a smoke screen it was OK.

Now please note that this is just a little bit better than 1/3 of velocity the 25pdr in early WW II mode (no muzzle brake, no supercharge).
Much like the German army, anti-tank use of field guns is pretty much an emergency thing. Battery is being overrun by surprise attack.
Germans went a little overboard on the self defense thing, doctrine calling for each and every field gun, no matter how large, to have 5 AP rounds in the ready area/storage, even if they almost needed a tractor to turn the gun and a hoist to put the shell in the breech.

 

[Elan Vital]

Were these two also experimental types?

Yes, the first vehicle set to enter production with the "self-propelled" 75 was the ARL V 39, in October 1940.
The 75mm for fortification assault tanks was not used at all because those tanks switched to the 105 or 90mm armament.

 

[tomo pauk]

Yes, the first vehicle set to enter production with the "self-propelled" 75 was the ARL V 39, in October 1940.
The 75mm for fortification assault tanks was not used at all because those tanks switched to the 105 or 90mm armament.

Thanlk you again.
BTW - is there an accessible place to take a look at the different, new (for the time) French ammo types? Anything between 7.5mm to 155 mm is a fair game