British 1936-42 purchase options, logistics and export/import of military hardware

[MikeMeech]

A lot of this had to do with trying to reinvent the wheel, while having the faulty doctrine that put premium on the ability to move and shoot, meaning that small & light tank guns are needed. Expecting that Army can do with feeble air support 20 years after the aircraft proved themselves time and again was another thing needing rework.


- 3.7in AA gun, again despite the industry capable for making modern 4in AA guns.


When one needs to make it all new - carriages, ordnances, ammo - things get expensive, late and complicated.

Hi
Reference the 3.7in AA gun. This was produced in both mobile and 'static' (they could be moved but were not mobile in field army terms) versions. About the same time the this gun was being developed and produced the army were also developing a 4.7in AA gun, however, due to the priority going to the 3.7in the prospect of getting it into service was slender. The Army therefore adopted the naval 4.5in for defence of rear areas, naval bases etc. This was being replaced during 1944-45, by the 5.25in, another adapted naval weapon. It should also be noted that the 3.7in Gun Mk.6 was a 4.5in gun with with a 3.7in barrel, this gave the shell an effective ceiling of 45,000 feet, compared with 32,000 feet of the earlier 3.7in. The book 'British and American Artillery of World War Two' by Ian V Hogg, gives a fair bit of detail on this and other weapons.
British AA guns available just before the BoB are listed below:

Source: 'History of the Royal Regiment of Artillery: Anti-Aircraft Artillery 1914-55' by Brigadier N W Routledge, page 379.

Mike

 

[EwenS]

The first 5.25" guns used by the British Army were 3 twin naval turrets that were surplus to Admiralty requirements in 1942. These were placed around London including one at Primrose Hill.

QF 5.25-inch naval gun - Wikipedia

en.m.wikipedia.org

The versions of the 5.25" for the Royal Artillery had a slightly higher muzzle velocity (2,850fps v 2,672fps) than the naval versions. There were two Royal Artillery versions - a pure AA mount and a dual purpose coast defence / AA version. Both required extensive construction works to contain underground engine rooms to supply electrical & hydraulic power, magazines etc. So in that respect they were not like the static 3.7" and 4.5" AA guns.

According to Routledge, Brigadier NW. 1994. History of the Royal Regiment of Artillery – Anti-Aircraft Artillery 1914–55 only 16 had been installed by the end of 1943 with just 164 produced by the end of WW2. One gun found its way to Port Moresby, New Guinea by Aug 1944. 7 more were installed at Gibraltar post-war where some can still be seen today.

5.25-Inch HAA Mk 5, Princess Anne’s Battery

5.25-Inch HAA Mk 5, Princess Anne’s Battery

www.ministryforheritage.gi

So I'm not sure that they could be described as "replacements" for the 4.5" weapons.

 

[tomo pauk]

The variety of the British gun calibers & ammo sizes above 75mm was astonishing.
3in guns in 3 pre-war calibers, then 4 ww2 calibers (counting the 75mm here), 18 pdr, 25 pdr, 3.7 in howitzer and AA gun. Then - 4, 4.5 how, cannon and AA gun, 4.7, 5, 5.5in guns. Ww1 6 in stuff in different flavors. This is just for the Army.

Granted, guns are made for different roles, and the march of technology certainly made older guns obsolete. However, only the UK among the big powers was okay with foregoing older 'diameters'. With enough of time, resources and money, that would've probably been a good move, but time is always short.
From my point of view, I'd try to keep it simple for the Army:
- make the new, high-capacity ammo for the 18 pdr, keep up with new carriage
- a 4 or 4.5 in gun-howitzer, for about 13 km range
- a 6in gun-howitzer, for about 15 km range
- see with the Navy about the joint project of the heavy AA gun (dual purpose for the RN), a modern 4in gets my vote

Tanks will need a mid-power 3in gun, mountain troops will need a suitable howitzer (I'd go with a modern 18 pdr howitzer). British were the only army without a small infantry gun, so there is a place to improve.

Every gun needs to have a small % of the AP ammo available, and crews need to be trained to attack moving targets. Tanks are also vulnerable to the heavy HE shells, a thing that need to be established during the tests in 1930s.

 

[MikeMeech]

The variety of the British gun calibers & ammo sizes above 75mm was astonishing.
3in guns in 3 pre-war calibers, then 4 ww2 calibers (counting the 75mm here), 18 pdr, 25 pdr, 3.7 in howitzer and AA gun. Then - 4, 4.5 how, cannon and AA gun, 4.7, 5, 5.5in guns. Ww1 6 in stuff in different flavors. This is just for the Army.

Granted, guns are made for different roles, and the march of technology certainly made older guns obsolete. However, only the UK among the big powers was okay with foregoing older 'diameters'. With enough of time, resources and money, that would've probably been a good move, but time is always short.
From my point of view, I'd try to keep it simple for the Army:
- make the new, high-capacity ammo for the 18 pdr, keep up with new carriage
- a 4 or 4.5 in gun-howitzer, for about 13 km range
- a 6in gun-howitzer, for about 15 km range
- see with the Navy about the joint project of the heavy AA gun (dual purpose for the RN), a modern 4in gets my vote

Tanks will need a mid-power 3in gun, mountain troops will need a suitable howitzer (I'd go with a modern 18 pdr howitzer). British were the only army without a small infantry gun, so there is a place to improve.

Every gun needs to have a small % of the AP ammo available, and crews need to be trained to attack moving targets. Tanks are also vulnerable to the heavy HE shells, a thing that need to be established during the tests in 1930s.

Hi
The US Army was not short of different gun calibre sizes as well (the same calibre doesn't mean the same shell was used either):
A/tk - 37mm, 57mm, 76mm, 3in, 90mm and 105mm.
AA - 37mm, 40mm, 75mm, 3in, 90mm, 105mm and 120mm.
Field & medium Arty - 75mm (How), 75mm (Field gun), 105mm (How), 4.5in field gun and 155mm How.
Heavy & Super Heavy - 155mm guns, 8in (How), 8in (gun) and 240mm Howitzers.

Such is the nature of artillery.

Mike

 

[tomo pauk]

Hi
The US Army was not short of different gun calibre sizes as well (the same calibre doesn't mean the same shell was used either):
A/tk - 37mm, 57mm, 76mm, 3in, 90mm and 105mm.
AA - 37mm, 40mm, 75mm, 3in, 90mm, 105mm and 120mm.
Field & medium Arty - 75mm (How), 75mm (Field gun), 105mm (How), 4.5in field gun and 155mm How.
Heavy & Super Heavy - 155mm guns, 8in (How), 8in (gun) and 240mm Howitzers.

Such is the nature of artillery.

Mike

The 3in AA, tank- and anti-tank gun were chambered for the same ammo. Same for the 90mm guns. The 75mm field gun used the same ammo as the 75mm tank gun.
The high-power 3.7in AA gun was not used in a vehicle, and the high-power 17pdr was not used as an AA gun; obviously their ammo was not the same. The 5.5 in gun used the bespoke ammo.

You can note that I haven't listed the British under 75 mm stuff, nor their above 6 in stuff. If I did, the count would've grown by some 10-12 items. Just at 40 mm there were 4 (four) non-interchangeable ammo sizes/types. Three different sizes of 57mm ammo.

 

[Shortround6]

The British often kept around all kinds of obsolete "junk" for training and overseas (colonial) use. They often had no intention of making more or even making more ammo for some of this "stuff".
Some other nations did the same thing, except that nobody else had as many colonies that needed "policing". The US had a lot less 1880-1916 "stuff" sitting in warehouses and they often foisted some of the "junk" onto the different national guards/state militias.
Germany managed to come up 18 different 75-77mm field guns between about 1900 and 1939 if we include all of their foreign sales (many of which wound up in German possession in 1939-41).

Once wars broke out old stuff tended to hang around for a number of years for training/drill even if they never intended to use it combat.

Counting up all the old junk can make some countries look really bad. But sometimes they were trying to come up with a modern simplified artillery park but they ran out of time.
What the British Army fought WW II with is not what they wanted to fight it with. It was they had the blueprints for, the money for, and manufacturing space for. And this was after getting squeezed out for funding by the RAF and RN.

The US wasn't that smart. They adopted/modified things to make things simple even if it wasn't what they wanted.

 

[Shortround6]

Specific items.

make the new, high-capacity ammo for the 18 pdr, keep up with new carriage

Even in the late 20s the British did not want to keep the 18pdr, even with High capacity ammo ( high cost steel) the British were trying to replace both the field gun and the field howitzer with a common gun/bore size. The Army had gone through a number of design studies and prototypes, including a 3" gun on the 18pdr carriage firing a 16lb shell at 2200fps. for a hoped for range of 15,000yds. But this had too much recoil for the 18pdr carriage and the 16pdr shell was not powerful enough to compensate for the greater range. The British then went through a 4.1" howitzer (105mm) and then a 3.9" and then back to a 3.3" field gun and then they decided they would never get both the field gun and the Howitzer and they barely got the combined weapon as the purse holders want them to use as much existing equipment as possible (new 3.45" barrels in the old 18pdr barrel jackets on the 1919-1920 carriages.
This is a what if and with more money you can do different things. But the gun and gun carriage designers were pretty good (a few failures like the 95mm infantry gun) but they figured that the well known carriage of the 25pdr gun with it's turn table saved 5 1/2 ctw (616lbs) over the split trail they were considering at the time.

a 4 or 4.5 in gun-howitzer, for about 13 km range

Which is it? a 4" or a 4.5"? Following the cube law a 4.5" gun (and shell) is 42% larger/heavier than a 4in gun/shell. Unless you play funny games with the shell. Like the British did with their 4.5in Howitzer.
The British 25pdr MK II had a range of 12.25km. If you want a 4.5in gun/howitzer to fire a 50lb shell 13km you need a gun over twice the weight of 25pdr (and that is using the box trail and that turntable thing under the wheels.) Pretty much rules out horse traction in 1920s (Britain was using tractors for most heavy artillery movement at the end of WW I)

a 6in gun-howitzer, for about 15 km range

Not sure were the advantage over the existing 5.5in comes in. Existing 5.5in fired a 100lbs shell (lots of steel) 14.8km. Used a more modern shell shape than some of the old WW I stuff. All of the old WW I 6in stuff (at least the guns) were lucky they had 38 degrees of elevation, Going to 45 degrees helps but not a lot. The 60 degrees of traverse for the 5.5" was huge improvement.
The old 6in Howitzer was a rather nice weapon for it's age.

1940. It was only ever made in one Mark, It was a huge improvement over the 5" and 6" howitzers that came before it. And the Recoil system was used with only minor modifications for 60pdr MK II, the early 4.5" guns and the later 4.5" and 5.5" guns. It was only slightly inferior to the French and American 1917/1918 155mm howitzers. And they miss your range goal by about 4km. Big question is what kind of traverse do you want?
German 15cm Howitzer had a range of 13.3km so you need a bigger, heavier gun.

see with the Navy about the joint project of the heavy AA gun (dual purpose for the RN), a modern 4in gets my vote

Army guns can use higher velocity, easier to re tube.
In the 1930s people often went in the wrong direction, they were looking for high velocity to make up for aiming errors. They also thought that Aircraft operating altitudes would continue to improve.

Tanks will need a mid-power 3in gun,

Only if you are willing to pay for large, heavy tanks. This is relative. The British treasury didn't want to pay for even 18 ton tanks. Or at least not for many of them. Going for 24 ton tanks means that until 1939 you are going to get about 33% fewer tanks.

mountain troops will need a suitable howitzer (I'd go with a modern 18 pdr howitzer)

This goes several ways, see below.

British were the only army without a small infantry gun, so there is a place to improve.

British had a decent mountain Howitzer, which made a decent, if not great infantry gun, except...........
Mortars were taking over for both mountain and infantry guns. You traded gun weight for ammo weight. Poorer accuracy mortar could have more ammo for the same total weight.
Problems for the British is the lousy British 3in Mortar with abysmal range in the MK I version.
Next problem is that the British infantry battalion already had a variety of weapons it needed to man they didn't have enough man power to handle what they had already.
Infantry guns made sense in WW I when they were using carrier pigeons and semaphore flags to all in artillery missions (or runners). With field phones and radios the need for infantry guns got a lot less. Please note that the Japanese, Italians and Soviets often had fewer radios than the British did.
Granted the British were a bit fond of their antiques but the British 3.7in pack howitzer was used sometimes as and infantry gun, it was used as an airborne gun and it was used as a landing gun (only in drills?) by the RN (it was carried on board some ships). It was not declared obsolete until 1960.
The Improvement, the 95mm infantry howitzer (ground version of the 95mm tank howitzer) even though they made around 500 of them, went nowhere. The infantry didn't want them. And there were too many things wrong with them. The wheel track was too narrow and they tended to overturn while being towed in rough country. The Spring recuperator in the recoil system failed a number of times in the trials despite several changes in the springs. The 3 zone propelling charge and the 30 degrees of elevation did not offer the flexibility of the old 3.7" howitzer 5 zone system and 40 degrees of elevation and the 8 degrees of traverse + turntable was not as easy as the 40 degrees of traverse and the split trail.
The new gun fired a heavier shell a bit further but the gun was also a bit heavier. Perhaps they had tried for too much performance? What is the desired range for a Battalion/regimental gun? At what point is a target far enough away that infantry just calls for divisional artillery to take care of it?

 

[tomo pauk]

Even in the late 20s the British did not want to keep the 18pdr, even with High capacity ammo ( high cost steel) the British were trying to replace both the field gun and the field howitzer with a common gun/bore size. The Army had gone through a number of design studies and prototypes, including a 3" gun on the 18pdr carriage firing a 16lb shell at 2200fps. for a hoped for range of 15,000yds. But this had too much recoil for the 18pdr carriage and the 16pdr shell was not powerful enough to compensate for the greater range. The British then went through a 4.1" howitzer (105mm) and then a 3.9" and then back to a 3.3" field gun and then they decided they would never get both the field gun and the Howitzer and they barely got the combined weapon as the purse holders want them to use as much existing equipment as possible (new 3.45" barrels in the old 18pdr barrel jackets on the 1919-1920 carriages.
This is a what if and with more money you can do different things. But the gun and gun carriage designers were pretty good (a few failures like the 95mm infantry gun) but they figured that the well known carriage of the 25pdr gun with it's turn table saved 5 1/2 ctw (616lbs) over the split trail they were considering at the time.

Keep the 18 pdr as a plan B solution, not just because it aligns with frugality mindset very well. Go with a much more substantial weapon for the near future, and ASAP. We can only expect that other big powers will not sit idle with their artillery developments in the 1930s.

Which is it? a 4" or a 4.5"? Following the cube law a 4.5" gun (and shell) is 42% larger/heavier than a 4in gun/shell. Unless you play funny games with the shell. Like the British did with their 4.5in Howitzer.
The British 25pdr MK II had a range of 12.25km. If you want a 4.5in gun/howitzer to fire a 50lb shell 13km you need a gun over twice the weight of 25pdr (and that is using the box trail and that turntable thing under the wheels.) Pretty much rules out horse traction in 1920s (Britain was using tractors for most heavy artillery movement at the end of WW I)

4in will do.

Not sure were the advantage over the existing 5.5in comes in. Existing 5.5in fired a 100lbs shell (lots of steel) 14.8km. Used a more modern shell shape than some of the old WW I stuff. All of the old WW I 6in stuff (at least the guns) were lucky they had 38 degrees of elevation, Going to 45 degrees helps but not a lot. The 60 degrees of traverse for the 5.5" was huge improvement.

Instead of developing an all-new 5.5 in gun and it's ammo, as well as with tooling up the factories for everything new, go with the known thing that your industry had decades of experience, and can apply the newer techs easier, faster and cheaper. Use the money saved to design and produce the high-capacity shells.

German 15cm Howitzer had a range of 13.3km so you need a bigger, heavier gun.

Big guns are motorized, so no biggie. The modern 6in shell will be heavier than a modern 5.5in shell by 25%.

Only if you are willing to pay for large, heavy tanks. This is relative. The British treasury didn't want to pay for even 18 ton tanks. Or at least not for many of them. Going for 24 ton tanks means that until 1939 you are going to get about 33% fewer tanks.

I am willing to pay for tanks capable of carrying such a gun, and even 15 ton tanks can carry these. Mistake was designing tanks for pop guns, and worry later when bigger guns were supposed to be installed.

 

[Shortround6]

Keep the 18 pdr as a plan B solution, not just because it aligns with frugality mindset very well. Go with a much more substantial weapon for the near future, and ASAP. We can only expect that other big powers will not sit idle with their artillery developments in the 1930s.

The 25pdr was a sort of split the difference between a 75mm and a 100-105mm. More shell weight than the 75-76mm guns and a range somewhere between a 75-76mm field gun and a 100-105 howitzer. Artillery was often developed as part of systems, not individual weapons.

4in will do.

Basically a 100-105mm howitzer with several thousand more meters of range?

Instead of developing an all-new 5.5 in gun and it's ammo, as well as with tooling up the factories for everything new, go with the known thing that your industry had decades of experience, and can apply the newer techs easier, faster and cheaper. Use the money saved to design and produce the high-capacity shells.

While not common the 5.5 was not unknown in Britain although the RN use came in through the back door after commercial sales to Greece.
However by the late 20s and early 30s gun construction was changing over considerably. The WW I naval guns were wire wound.
As far as cost. The Price of several thousand rounds of ammo can exceed the cost of the guns. Cost of other parts of the 'system' can add to the total cost.
WW I carriages unless designed in the last 1-2 years are best left in the warehouse.

Instead of developing an all-new 5.5 in gun and it's ammo, as well as with tooling up the factories for everything new, go with the known thing that your industry had decades of experience, and can apply the newer techs easier, faster and cheaper.

Use the money saved to design and produce the high-capacity shells.

Big guns are motorized, so no biggie. The modern 6in shell will be heavier than a modern 5.5in shell by 25%.

I am willing to pay for tanks capable of carrying such a gun, and even 15 ton tanks can carry these. Mistake was designing tanks for pop guns, and worry later when bigger guns were supposed to be installed.

They can't in reality. The 75mm armed Valentine was not a good tank, it wasn't even a mediocre tank. It was slow, it had poor range, it fired slow, it had poor vision which was made worse by the commander being the loader. It had both low cannon ammo capacity and low MG ammo capacity.
It could not do some of the Jobs that the either the Crusader or Stuart could do. While the British loved the Stuart for certain things they disliked it for others, like the two man turret which was a problem in combat. The fast tanks could operate on the flanks which the Valentine could not do.
A 75mm armed Valentine is a well protected slow firing and slow moving SP gun.
Compared to a 2 man turret T-34 it doesn't seem too bad. Compared to a proper tank with a 3 man turret it leaves a lot to be desired.

 

[tomo pauk]

The 25pdr was a sort of split the difference between a 75mm and a 100-105mm. More shell weight than the 75-76mm guns and a range somewhere between a 75-76mm field gun and a 100-105 howitzer. Artillery was often developed as part of systems, not individual weapons.

No quarrels about that.
For this what-if, I'd say that it would've been better if they kept close to the new/original calibre, and not dialed that back a few times.

Basically a 100-105mm howitzer with several thousand more meters of range?

Yes. And I'm willing to pay the price in weight and, well, price.

They can't in reality.

British were installing the 3.7in howitzers in the tanks as light as 13 tons. The medium-power 3in should not demand much more.

 

[z42]

Instead of developing an all-new 5.5 in gun and it's ammo, as well as with tooling up the factories for everything new, go with the known thing that your industry had decades of experience, and can apply the newer techs easier, faster and cheaper. Use the money saved to design and produce the high-capacity shells.

If your existing guns in the size are all obsolete in several respects, and you have to design a new gun, shell, carriage, etc, then maybe whether the diameter of the barrel happens to match an older one doesn't matter that much?

I am willing to pay for tanks capable of carrying such a gun, and even 15 ton tanks can carry these. Mistake was designing tanks for pop guns, and worry later when bigger guns were supposed to be installed.

Historically, the well balanced tanks equipped with medium velocity 75mm guns ended up in the 25 ton range. E.g. M4, T-34, Cromwell. What are you preparing to sacrifice to get a 15 ton tank? Mobility? Armor? Ammo capacity? 3 man turret? One thing you could give up is the bow gunner, let the commander handle the radio. Probably not a huge improvement, but something.

And yes, such tanks would have been great had they been available from the start of the war. And in retrospect, having such vehicles available in France 1940 and later in the NA campaign could have been very useful, even at the cost of smaller numbers than the historical early war British tanks. But that's with a huge dose of retrospectivity.

 

[Shortround6]

British were installing the 3.7in howitzers in the tanks as light as 13 tons. The medium-power 3in should not demand much more.

Tomo, this a misconception. Wiki is in error.
The 3.7" whatever (Even British books do not agree.) but it seems to have been officially called the
" Q.F.,3.7-in MARK I Mortar"
A manual can viewed/downloaded here that covers the ammo fairly well.

https://ordnancesociety.org.uk/wp-content/uploads/2020/05/3.7-inch-mortar.pdf

This ammo and gun shares nothing in common with the 3.7in mountain gun except diameter.
The weapon fired basically a short stumpy 15lb projectile at 620fps (189ms) using a fixed charge of about 1.6 ounce. Or about 1/5 of the max charge of the 3.7in mountain gun.
The weapon is somewhat less powerful than the German 7.5cm infantry gun but uses a poorer shaped projectile.
Max range is often given as 2000yd (1829 meters). and we can see that the time of flight to that distance is over 10 seconds.
A medium powered 3in (Cromwell or Sherman gun) is going to weight between 4 and 5 times as much.
Please note that these weapons (devices?) were only used officially in the old Vickers medium tanks and the A-9 and A-10.
Perhaps some work shop/s stuck a handful in A-13s but that was not official.

This weapon was replaced by the British tank wonder weapon, the QF 3-in close support howitzer. Which fired a 13.75lb projectile at a similar speed (sources disagree) for about the same range.
Basically for point targets both were very, very, very short ranged weapons and as shown very long times of flight for area fire at anything even approaching half range.

A real problem with trying to put large guns in small tanks is that they don't hold a lot of ammo and since the British were still trying to figure basic things, like getting fast artillery support fire or how to cooperate with infantry, what the tank/s carried for ammo was it. Nobody else was usually going to be able to bail them out.
In a "what if" perhaps the British would do better to fix tactics/doctrine/communications sooner (and a number of other things) rather than trying to stuff large guns in small tanks.
Unfortunately it took the British armor until late 1942 to really get into combined arms. Sticking even medium powered 3in guns into tanks and outrunning their artillery support and infantry support is still not going to end well.

 

[Shortround6]

If your existing guns in the size are all obsolete in several respects, and you have to design a new gun, shell, carriage, etc, then maybe whether the diameter of the barrel happens to match an older one doesn't matter that much?

That is pretty much the case for the British, they had nowhere near the inventory of old guns the French did so they wouldn't be throwing away that much.

Historically, the well balanced tanks equipped with medium velocity 75mm guns ended up in the 25 ton range. E.g. M4, T-34, Cromwell. What are you preparing to sacrifice to get a 15 ton tank? Mobility? Armor? Ammo capacity? 3 man turret? One thing you could give up is the bow gunner, let the commander handle the radio. Probably not a huge improvement, but something.

British just about always stuck the radio in the turret so the bow gunner just handled the bow gun, not a all hard to give up except to doctrine (those stupid little machinegun turrets)

And yes, such tanks would have been great had they been available from the start of the war. And in retrospect, having such vehicles available in France 1940 and later in the NA campaign could have been very useful, even at the cost of smaller numbers than the historical early war British tanks. But that's with a huge dose of retrospectivity.

In France in 1940 if the British could possibly make a mistake with their tanks they probably made it in the 1st Armored division. Some of this was due to time. Radios not working (or not enough of them) not having combat load outs of ammo (they thought they were going to a training camp) Not having their own infantry, not having their own artillery (still on the docks in England?) a lot of driving to and fro to help French moral that wore out/broke tanks and separated the Tank Regiments as units.
Not even getting into the poor doctrine/tactics or the stupid fire on the move doctrine.

Changing the guns doesn't fix any of that and would not help in Greece or for much of first months in North Africa.

 

[tomo pauk]

If your existing guns in the size are all obsolete in several respects, and you have to design a new gun, shell, carriage, etc, then maybe whether the diameter of the barrel happens to match an older one doesn't matter that much?

Diameter of the barrel does not mean much indeed. What might, or perhaps should matter is the timing of the weapon, and ability of industry to start churning up both the new guns and ammo for them in good quantities. The more it is to change, or new stuff to introduces, the more time & money is needed.

Historically, the well balanced tanks equipped with medium velocity 75mm guns ended up in the 25 ton range. E.g. M4, T-34, Cromwell. What are you preparing to sacrifice to get a 15 ton tank? Mobility? Armor? Ammo capacity? 3 man turret? One thing you could give up is the bow gunner, let the commander handle the radio. Probably not a huge improvement, but something.

The 15 ton tank is in the #2 place among the tanks, behind a 25+ ton tank IMO. I have no illusions that a 15 ton tank armed with something that is as powerful as the French 75mm will be a balanced tank. OTOH,. a tank that has a higher MV 57mm gun, like the new RN gun or the Army's 6pdr, will still demand the same internal volume. So we will not have 3-men turret if the tank is well armored, or perhaps we can go with the Cruiser tank idea, that sacrifices armor for having the 3-men turret. Ammo capacity can be as it was on the Valentine.
Again, the focus need to be at the 25+ ton tank, and the 15 ton tanks should be made by factories that can't handle the heavier tank.

Tomo, this a misconception. Wiki is in error.
The 3.7" whatever (Even British books do not agree.) but it seems to have been officially called the
" Q.F.,3.7-in MARK I Mortar"
A manual can viewed/downloaded here that covers the ammo fairly well.
https://ordnancesociety.org.uk/wp-content/uploads/2020/05/3.7-inch-mortar.pdf
This ammo and gun shares nothing in common with the 3.7in mountain gun except diameter.
The weapon fired basically a short stumpy 15lb projectile at 620fps (189ms) using a fixed charge of about 1.6 ounce. Or about 1/5 of the max charge of the 3.7in mountain gun.
The weapon is somewhat less powerful than the German 7.5cm infantry gun but uses a poorer shaped projectile.

Thank you.

 

[z42]

In France in 1940 if the British could possibly make a mistake with their tanks they probably made it in the 1st Armored division. Some of this was due to time. Radios not working (or not enough of them) not having combat load outs of ammo (they thought they were going to a training camp) Not having their own infantry, not having their own artillery (still on the docks in England?) a lot of driving to and fro to help French moral that wore out/broke tanks and separated the Tank Regiments as units.
Not even getting into the poor doctrine/tactics or the stupid fire on the move doctrine.

Changing the guns doesn't fix any of that and would not help in Greece or for much of first months in North Africa.

Sure, no objection there. It's easy to forget even the best tank in the world isn't worth much if it's employed incorrectly. It needs to be part of a well thought out combined arms system. OTOH without at least a half decent tank even a good combined arms doctrine will falter.

Of course, the doctrine informs which kind of tank is to be designed. And a good tank will allow the development of doctrine to make use of it. And combat experience will show whether peace time thought is worth anything, and (hopefully?) lead to better doctrine and equipment. So we have a chicken, an egg, and a potato; which comes first?

 

[z42]

Diameter of the barrel does not mean much indeed. What might, or perhaps should matter is the timing of the weapon, and ability of industry to start churning up both the new guns and ammo for them in good quantities. The more it is to change, or new stuff to introduces, the more time & money is needed.

I think it's understandable. After WWI Britain had, like the other powers, lots of surplus equipment, and then there was the post war economic slump. When the clouds started gathering in the mid 30ies what they had was obsolete, and they had to start with a clean sheet.

The 15 ton tank is in the #2 place among the tanks, behind a 25+ ton tank IMO. I have no illusions that a 15 ton tank armed with something that is as powerful as the French 75mm will be a balanced tank. OTOH,. a tank that has a higher MV 57mm gun, like the new RN gun or the Army's 6pdr, will still demand the same internal volume. So we will not have 3-men turret if the tank is well armored, or perhaps we can go with the Cruiser tank idea, that sacrifices armor for having the 3-men turret. Ammo capacity can be as it was on the Valentine.
Again, the focus need to be at the 25+ ton tank, and the 15 ton tanks should be made by factories that can't handle the heavier tank.

If you want a 15 ton tank at the start of the war, which given what they knew at the time and budgets is arguably more realistic than going straight for a 25 ton one, I think you'll have to sacrifice the idea of the medium velocity 75mm. The historical high velocity 6pdr is indeed no improvement size wise over the medium velocity 75mm, so that is out too. So we're left with something like a medium velocity 6pdr. Or then just giving a HE shell to the historical 2pdr.

 

[tomo pauk]

If you want a 15 ton tank at the start of the war, which given what they knew at the time and budgets is arguably more realistic than going straight for a 25 ton one, I think you'll have to sacrifice the idea of the medium velocity 75mm. The historical high velocity 6pdr is indeed no improvement size wise over the medium velocity 75mm, so that is out too. So we're left with something like a medium velocity 6pdr. Or then just giving a HE shell to the historical 2pdr.

British went with the 26 ton Matilda II for the start of war. So the '25+' ton tank - but a bit more refined machine - is not such a stretch IMO.
Medium velocity 6pdr existed a few decades earlier, there is some elbow room to make the 'quasi APCR' shot (ie. something that can use machine steel and still not shatter on impact), for perhaps 800 m/s vs. 540 m/s for the full-weight shot? It will kill any German tank in 1940 already as-is. A bit souped-up APC should've also worked - see here the French going from 590 m/s to 700 on the tankers 47mm.

 

[z42]

British went with the 26 ton Matilda II for the start of war. So the '25+' ton tank - but a bit more refined machine - is not such a stretch IMO.
Medium velocity 6pdr existed a few decades earlier, there is some elbow room to make the 'quasi APCR' shot (ie. something that can use machine steel and still not shatter on impact), for perhaps 800 m/s vs. 540 m/s for the full-weight shot? It will kill any German tank in 1940 already as-is. A bit souped-up APC should've also worked - see here the French going from 590 m/s to 700 on the tankers 47mm.

Matilda was quite lacking in the firepower and mobility department. But yes, it does show that the British army was capable of logistically supporting such a heavy tank already early in the war.

And yes, several options for a medium velocity 6pdr gun suitable for the small early war tanks.

Ideally, in retrospect, forget the doctrine requiring separate cruiser and infantry tanks, and instead adopt a "heavy cruiser" as the main tank. With the help of a time machine, take the Centurion and produce a few downscaled versions for different phases of the war:

All of them with 3 man turrets, with main gun and coax Mg. Maybe a roof mounted Mg for the loader to use? Sloped front armor, no bow gun (thus 4 man crew).

- Early war tank. Medium velocity 6pdr, Liberty engine, around 20 tons.

- Mid war tank. QF 75mm gun, Meteor (if available yet) or uprated Liberty engine, around 30 tons.

- Late war tank. The real Centurion, with the 17pdr gun.

 

[tomo pauk]

- Early war tank. Medium velocity 6pdr, Liberty engine, around 20 tons.
- Mid war tank. QF 75mm gun, Meteor (if available yet) or uprated Liberty engine, around 30 tons.
- Late war tank. The real Centurion, with the 17pdr gun.

I'd go a bit more ambitious
MBTs:
- 25+ ton tank, Liberty is okay (twinned AEC petrol engine as back-up), the new Navy's 6 pdr or the mid-power 3in gun
- 40 ton not-Churchill: main gun that is in the ballpark of the 77mm HV or the US 3in; hopefully Meteor or some V12 diesel
- 50 ton tank for late 1943: with either something like the 17 pdr or an 84mm cannon (that is as powerful as the Tiger's cannon or the US 90mm), a 600-700 HP engine

A 15 ton tank to bulk up the numbers in the late 1930s; guns might be the old navy's 6pdr, or perhaps the semi-auto 2pdr; powerplant - includes the twinned bus engine.
Horstmann suspension for all, with greater emphasis on armor protection than on speed. APDS ammo by 1943/early 1944.

A 7-8 ton tank that is tailored towards being a self-propelled piece, for AT guns, artillery, as well as AA use. This one can be fast.

 

[Shortround6]

British went with the 26 ton Matilda II for the start of war. So the '25+' ton tank - but a bit more refined machine - is not such a stretch IMO.

Well the Matilda was kind of a special case. It was small (volume) for it's weight. It was a bit easier (not a lot easier) to transport than a larger tank of the same weight. Still needs the same bridging equipment. The Matilda only gained it's reputation because of it's armor for the most part. It carried a bit less ammo than the Cruiser tanks. You also need a bigger hull to fit in a bigger powerplant if you want a faster tank and the increased hull size is going to run up weight quick.

A bit souped-up APC should've also worked - see here the French going from 590 m/s to 700 on the tankers 47mm.

And the French souped-up 47mm tank gun still wasn't as good as the British 40mm.
Some of the proposed 6pdr/57mm tank guns aren't much better than the British 40mm and weigh more, need larger/heavier turret, and restrict ammo capacity.

- Early war tank. Medium velocity 6pdr, Liberty engine, around 20 tons.

Great, ditch the medium velocity 6pdr. Keep the 2pdr, Keep the basic A 13. work on fixing the existing Liberty and not start dissipating design and development work on 3 different bespoke tank engines, while trying to sort out the modified Liberty.
For the A 13, add more armor, add 5 wheel if needed. Get rid of the stupid shoulder elevation system.

- Mid war tank. QF 75mm gun, Meteor (if available yet) or uprated Liberty engine, around 30 tons.

Get the Centaur/Cromwell into production sooner. Maybe by killing the Covenanter on the drawing board. And perhaps a few other projects.

Late war tank. The real Centurion, with the 17pdr gun

Just get the tank guys and the gun guys to talk to each other sooner. A close to Comet with the 77mm in production at the end of 1943?
Put a sloped nose on it instead of the left over Cromwell nose.

A 15 ton tank to bulk up the numbers in the late 1930s; guns might be the old navy's 6pdr, or perhaps the semi-auto 2pdr; powerplant - includes the twinned bus engine.
Horstmann suspension for all, with greater emphasis on armor protection than on speed. APDS ammo by 1943/early 1944.

For some reason everybody thinks the standard British 6pdr was a bad gun. It was being designed in 1938, it was test fired in 1939. It should have gone into production in late 1940 or early 1941 and most British service tanks in 1942 should have had the 6pdr in late winter/early Spring of 1942, not just showing up in the late fall of 1942.
As far as the 2pdr goes. I may be being a bit of stickler here. The Standard 2pdr tank/AT gun was semi-auto. This may be a translation issue. For artillery/AT guns/AA guns semi-auto means that the gun is auto ejecting. Gun fires and as the barrel recoils the breech block drops down and the empty casing is ejected. As the Barrel runs forward the breech block stays down and stays down until the loader slams a new round into the breech. The act of slamming the new round into breech pushes either the ejectors forward or trips a latch allowing the spring loaded breech block to slam shut.
Please note that the French 75 was NOT semi-automatic even though it was "quick firing" weapon. It depended on a gunner's hand to operated the handle to open and close the Breech. US/British tank cannon could fire French 75mm ammo but the tank guns had new breech blocks (they also had new barrels).
The Pom-Pom gun was full automatic, it was just slow. It was also heavy and bulky and would need a largish turret.

A 7-8 ton tank that is tailored towards being a self-propelled piece, for AT guns, artillery, as well as AA use. This one can be fast.

I keep saying, there is a lot more to self propelled AT guns, Artillery and AA guns that just getting the chassis and gun to drive down the road (or field) without falling over.
You need a decent amount of ammo, or you need a crap load of ammunition vehicles. Which runs up the total cost of purchasing the needed vehicles for a battery/company/battalion.
You also have to have for some vehicle, enough crew and enough space for the crew to work. Jamming a large gun into a small chassis/hull can often restrict the rate of fire for artillery pieces which means you either can't fire a lot of rounds in "burst fire" or you need more SP guns to get the same amount of rounds down range than you need towed guns to get the same volume of fire.

A lot of the proposals for the British seem to ignore that the British were NOT supplying very good ammo to their tanks.
The 2pdr started with APHE, a small charge of HE was supposed to go off after the shell penetrated. This was common to a lot of other countries tank and AT tank ammo in the 37mm size, not all. But by 1939 trials had shown problems with the 2pdr APHE. They had a high dud rate. When going through armor at steep slopes the shell body distorted and popped the fuse (and sometimes the HE) out the back before it detonated. There was some argument as to the small charge being large enough to kill/disable the enemy crew (or most of them).
So before ever going to war the British decided to use just plain AP shot with a tracer screwed on the back. In 1940 and early 1941 there 3 types of 2pdr AP ammo in use. The old APHE, available in limited numbers but a least some showed up in France and Egypt. Some was used in training. Some was turned into training ammo buy pulling the fuse and HE out of the shells and filling the space with sand and threaded plug and refitting the tracer element. And lastly the AP shot (no cap, no ballistic cap). There was NO HE shell in the early years.
Granted this is a what if but the solution seems to be to take old, crappy 6pder guns and/or ammo ( or build new guns to old dimensions), design and build new HE shells, and then design/build new AP projectiles, some of which will be some sort of APCR shot (tungsten steel core?) to get around the fact that the old 6pdr guns/ammo aren't any better than the 2pdr gun using cheap solid one piece projectiles.
The 6pdr offers better HE but still small fraction of what a 75mm (12-16pdr) holds and the 6pdr ammo would have been a really poor smoke round (none every built?) so you still need some sort of 75-94mm smoke thrower (you still need a close support tank).

Cheapest, easiest solution for British tank guns was to use the 2pdr, Fit either 40mm Bofors shells or 2pdr Pom-Pom shells for HE, design and build APCBC ammo and issue it by the beginning of 1941.
After Dunkirk (if not before) scrap the fancy 360 degree carriage for the 2pdr AT gun and build 60 degree split traverse carriages that and much cheaper and lighter and use the freed up production capacity to get the 6pdr into production quicker.