Sir John Valentine Carden survives.

With regards to the 75mm and not 76.2mm the answer could be as simple as Vickers was already working on it and simply ran with what they had - an off the shelf design so to speak

And as for logistics and production - a new round and gun production line would be required regardless of it being 75mm or 76.2mm and therefore "new production" not existing production - so it does not matter which was chosen
I think the issue is that Vickers had both calibres "off the shelf" for the Model 1931. And the the RO chief requested a 3" round to be used. So Vickers necked it down to 75 mm?

Doesn't really matter but just seems a bit odd. TBH if you can turn a 57mm into a 75 mm then switching from 75mm to 3" is childsplay
 
With regards to the 75mm and not 76.2mm the answer could be as simple as Vickers was already working on it and simply ran with what they had - an off the shelf design so to speak

And as for logistics and production - a new round and gun production line would be required regardless of it being 75mm or 76.2mm and therefore "new production" not existing production - so it does not matter which was chosen
Vickers choosing to run with something and the army accepting it are two different things.

If Vickers are designing around an existing case, the 3" 20cwt case, and that already has a round of the desired weight and vellocity then why not design the gun to use the already in production round?
That way you only need to expand some production rather than start up something new. Yes both require work but one needs quite a bit less.
Now that's not to say current production will be sufficient but adapting and expanding must surely be preferable to starting completely from scratch.
 
With regards to the 75mm and not 76.2mm the answer could be as simple as Vickers was already working on it and simply ran with what they had - an off the shelf design so to speak

And as for logistics and production - a new round and gun production line would be required regardless of it being 75mm or 76.2mm and therefore "new production" not existing production - so it does not matter which was chosen
the question comes is why are they adding a new 75mm shells into their logistics when they already have 76.2mm shells of similar performance would it not be more practical to stick with one to avoid issues of getting the two mixed up?
 
the question comes is why are they adding a new 75mm shells into their logistics when they already have 76.2mm shells of similar performance would it not be more practical to stick with one to avoid issues of getting the two mixed up?
Okay - fair one - but they also went with a 75mm HV gun historically despite all this 'existing' production (I appreciate that US 75mm was a driver but still)

They are adding a new shell into their logistics regardless of the gun and calibre chosen - and historically there was a smorgasbord of ammo types anyway and they seemed to manage.

Chaps - less angst was expended by the Admiralty on building HMS Unicorn than this part of the thread has on 75mm HV guns!
 
Just a friendly suggestion.....

If Allan has chosen to go 75mm then let's respect his decision and let him make that call. He likely has his reasons.

If you don't like the adoption, then add a rationale....

"As tool and die makers in the UK were already over capacity with existing orders, Vickers reached out to US suppliers who replied that although 76mm sets would take longer, that a first full 75mm tooling set for both guns and projectiles (not cases) could be on a ship within 30-days of receipt of payment. As the performance of both shells would be nearly identical, as time was of the essence, as it would lower the burden on UK tool & die makers, and as the US factories could later be asked to provide complete guns or ammunition if required, the 75mm bore was selected and designers got to work on an efficient and lightweight design suitable for their new tanks."
 
Just a friendly suggestion.....

If Allan has chosen to go 75mm then let's respect his decision and let him make that call. He likely has his reasons.

If you don't like the adoption, then add a rationale....

"As tool and die makers in the UK were already over capacity with existing orders, Vickers reached out to US suppliers who replied that although 76mm sets would take longer, that a first full 75mm tooling set for both guns and projectiles (not cases) could be on a ship within 30-days of receipt of payment. As the performance of both shells would be nearly identical, as time was of the essence, as it would lower the burden on UK tool & die makers, and as the US factories could later be asked to provide complete guns or ammunition if required, the 75mm bore was selected and designers got to work on an efficient and lightweight design suitable for their new tanks."
Perfectly plausible.

UK may even prevent the 75mm from being deployed and delay the Victor (TTL's great tank scandal) whilst the 75mm HV is built under license for the M4
 
the question comes is why are they adding a new 75mm shells into their logistics when they already have 76.2mm shells of similar performance would it not be more practical to stick with one to avoid issues of getting the two mixed up?
Maybe Allan is setting up the British to have issues over mixing up the shells - possibly even to lose a battle or two based on that. Just because Carden is still alive, it doesn't make the British immune to making new and creative mistakes in the middle of a war.
 
Okay - fair one - but they also went with a 75mm HV gun historically despite all this 'existing' production (I appreciate that US 75mm was a driver but still)

They are adding a new shell into their logistics regardless of the gun and calibre chosen - and historically there was a smorgasbord of ammo types anyway and they seemed to manage.

Chaps - less angst was expended by the Admiralty on building HMS Unicorn than this part of the thread has on 75mm HV guns!
How about a 75.5 m!

just like the Royal Navy went to 7.5” etc just to annoy the Germans and French
 
Jesus fucking christ. Anywhere else on the internet I would be surprised to find grown adults losing their minds over 0.047244” but it’s absolutely par for the course here.
Oh my god no, one twentieth of an inch, stop the presses, there is clearly no way any industrial nation in the mid-twentieth century could possibly accommodate such a difference.
How dare anyone suggest in a work of fiction that the UK could possibly add one more calibre to its OTL WW2 collection of .303, 8mm, .38, 9mm, .45, .455, .50, 15mm, 20mm, 40mm, 2”, 6pdr, 3”, 25pdr, 3.7”, 4”, 4.5”, 4.7”, 5.25”, 6”, 7.2”, 8”, 9.2”, 14”, 15”, 16” (and probably a bunch more I have missed), that’s clearly CRAZY TALK.
No wonder most timeline authors lose interest in continuing….
 
Jesus fucking christ. Anywhere else on the internet I would be surprised to find grown adults losing their minds over 0.047244” but it’s absolutely par for the course here.
Oh my god no, one twentieth of an inch, stop the presses, there is clearly no way any industrial nation in the mid-twentieth century could possibly accommodate such a difference.
How dare anyone suggest in a work of fiction that the UK could possibly add one more calibre to its OTL WW2 collection of .303, 8mm, .38, 9mm, .45, .455, .50, 15mm, 20mm, 40mm, 2”, 6pdr, 3”, 25pdr, 3.7”, 4”, 4.5”, 4.7”, 5.25”, 6”, 7.2”, 8”, 9.2”, 14”, 15”, 16” (and probably a bunch more I have missed), that’s clearly CRAZY TALK.
No wonder most timeline authors lose interest in continuing….
Don't forget, the British had two different .50-caliber cartridges (and yeah, you missed a fair few, mostly British Army artillery calibers, but I won't list them).

But in all seriousness, yeah. I agree, seriously I actually didn't expect to encounter this at all here. I guess this is why forums is a place where (unless your doing a timeline here on AH), that you should leave your sanity at the door.
 
Question on the gun, is the 3" 20cwt gun actually in production at the time, or like the 18-pounder, is it simple a hold-over from the previous war?
 
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Question on the gun, is the 3" 20cwt gun actually in production at the time, or like the 18-pounder, is it simple a hold-over from the previous war?
Hand over, around 200 with the army though most have been converted into the AT 3 inch 16cwt.
The navy also has just under 1000 guns in service in various marks.

New ammo is being produced though including the new AT round.

Realistically though the only reason the 3 inch is being discussed is the ammo. The gun itself, even in lightened AT gun form is far too heavy for tank use. The mounting in the Churchill for instance was rubbish being cramped and front heavy. Also the rifling was a bit prone to not lasting with highish velocity rounds. The 2550ft/s of the 12.5 pound round won't make it long lived for instance. In WW1 the gun got a new 16lb round at 2000ft/s and that solved the barrel wear problem.
 
Hand over, around 200 with the army though most have been converted into the AT 3 inch 16cwt.
The navy also has just under 1000 guns in service in various marks.

New ammo is being produced though including the new AT round.

Realistically though the only reason the 3 inch is being discussed is the ammo. The gun itself, even in lightened AT gun form is far too heavy for tank use. The mounting in the Churchill for instance was rubbish being cramped and front heavy. Also the rifling was a bit prone to not lasting with highish velocity rounds. The 2550ft/s of the 12.5 pound round won't make it long lived for instance. In WW1 the gun got a new 16lb round at 2000ft/s and that solved the barrel wear problem.
Fitting a hold-over weapon when you don't have the tooling to produce more would seem to me to not be a particularly brilliant idea. The Model 1931 meanwhile has not only the tooling, but an actual (admittedly low volume) production line set up.
 

Ramontxo

Donor
Jesus fucking christ. Anywhere else on the internet I would be surprised to find grown adults losing their minds over 0.047244” but it’s absolutely par for the course here.
Oh my god no, one twentieth of an inch, stop the presses, there is clearly no way any industrial nation in the mid-twentieth century could possibly accommodate such a difference.
How dare anyone suggest in a work of fiction that the UK could possibly add one more calibre to its OTL WW2 collection of .303, 8mm, .38, 9mm, .45, .455, .50, 15mm, 20mm, 40mm, 2”, 6pdr, 3”, 25pdr, 3.7”, 4”, 4.5”, 4.7”, 5.25”, 6”, 7.2”, 8”, 9.2”, 14”, 15”, 16” (and probably a bunch more I have missed), that’s clearly CRAZY TALK.
No wonder most timeline authors lose interest in continuing….
Do you mean the same Nation famous for using the naval 4,5 as heavy AA in an Army having a 4,5 inch long range gun but using different ammunition?
Not to mention that the navy 4,5 guns were divided between those that used fixed and separate Ammunition.
 
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Fitting a hold-over weapon when you don't have the tooling to produce more would seem to me to not be a particularly brilliant idea. The Model 1931 meanwhile has not only the tooling, but an actual (admittedly low volume) production line set up.
Oh I am by no means suggesting fielding the 3 inch 20cwt as the tank gun. The Model 1931 is definitely the way to go, the only question is which Model 1931. The gun was both a 75mm and 3 inch weapon after all so the calibre can be changed between the two.
The big issue for me is the case in use is the 3" 20cwt case necked down to 75mm and is firing a 12.5 pound projectile at 2550ft/s
The 3" already has an AT round that is firing a 12.5 pound projectile at 2550ft/s roughly. This round is already in production as is other 3" 20cwt ammo like a 16 pound HE round, a star shell and a shrapnel round.

My argument is rather than reinventing the wheel just make use of what is already their. The model 1931 is already being adapted to fire a round from the 3" 20cwt case. Why not just adapt it to fire the 3" 20cwt ammo already being built. We already know that 12.5lb's at 2550ft/s is acceptable so it isn't like anything is being lost or gained. Yes in future you can increase the performance of the AT round if you want or improve the HE round but for now they are better than what is out their and are available and in production already. Expanding and in some cases modifying production lines is surely preferable to setting up a whole new set of production for almost identical ammo.
 
Oh I am by no means suggesting fielding the 3 inch 20cwt as the tank gun. The Model 1931 is definitely the way to go, the only question is which Model 1931. The gun was both a 75mm and 3 inch weapon after all so the calibre can be changed between the two.
The big issue for me is the case in use is the 3" 20cwt case necked down to 75mm and is firing a 12.5 pound projectile at 2550ft/s
The 3" already has an AT round that is firing a 12.5 pound projectile at 2550ft/s roughly. This round is already in production as is other 3" 20cwt ammo like a 16 pound HE round, a star shell and a shrapnel round.

My argument is rather than reinventing the wheel just make use of what is already their. The model 1931 is already being adapted to fire a round from the 3" 20cwt case. Why not just adapt it to fire the 3" 20cwt ammo already being built. We already know that 12.5lb's at 2550ft/s is acceptable so it isn't like anything is being lost or gained. Yes in future you can increase the performance of the AT round if you want or improve the HE round but for now they are better than what is out their and are available and in production already. Expanding and in some cases modifying production lines is surely preferable to setting up a whole new set of production for almost identical ammo.
The question is, is it the same case? It's certainly a different shell (75 x 495 mm for the Model 1931, 76.2 x 420 mmR for the 3" 20cwt), so it might not be the same case.
 
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