Sir John Valentine Carden Survives. Part 2.

[marathag]

It has been, but my Carden is concerned with an effective dual-purpose tank gun. The 17-pdr's HE capability was always going to be limited. He is also thinking about the next gun. Yes, we know the 17-pdr is enough gun for the rest of the war, he doesn't. If the Venom is 5-6 inch armoured, then there's a good chance German tanks will be likewise (King Tiger has over 7-inches in places?). The capture of some 88mm Flak guns in North Africa will help give the Allies a real knowledge of what they're up against. I think looking a jumping the 95mm towards a 102mm, or better yet, 105mm gun is well worth looking at, even at this point.

The M4 105mm Howitzer used in the M4 Sherman weighed 1140 pounds
the 25pdr used with British SPGs was 1124 pounds

17 pdr was 2032 pounds in weight , US M3 90mm was 2450 pounds. the high power US 90mm was the the T15E2 90mm 3270 pounds and far more powerful.

The real monster was the US 105mm T5E1 used in the T28 GMC, 6484 pounds.

The energy of the various cannons
-Br- 77mm HV – 7.71kg at 785m/s = 2,383,866 joules
-Br- 17pdr QF – 7.71kg at 884m/s = 3,021,246 joules
-US- 90mm M3 – 10.914kg at 853m/s = 3,983,662 joules
-US- 90mm T15E2 – 10.9kg at 975m/s = 5,196,586 joules
-Br- 32pdr QF – 14.515kg at 878m/s = 5,608,738 joules
-US- 105mm T5E1 – 17.7kg at 914m/s = 7,416,335 joules

With new steels and developments, the British L7 weighed 2826 pounds, and had almost the same power as the T5E1, 7,096,896 joules of muzzle energy
It replaced the 20 pounder, that was pretty much an improved 17 pounder
The 20 pounder weighed 2885 pounds with 4,545,000 joules of muzzle energy

 

[MarcH]

It's such a limited gain over a 75mmHV that making it as the centrepiece for a new tank would be very short sighted.

Not really, at least not from the point of view of the current TL. If, as has been suggested, the 75mm HV is comparable or a bit less powerful than the OTL 75mm HV that makes it a bit less powerful than the 77mm HV which was less powerful than the 17pdr. Even without that knowledge and the knowledge of the "accuracy issues" of the 17pdr it is still a notable and worthwhile step up over the 75mm HV.

It has been, but my Carden is concerned with an effective dual-purpose tank gun. The 17-pdr's HE capability was always going to be limited. He is also thinking about the next gun. Yes, we know the 17-pdr is enough gun for the rest of the war, he doesn't. If the Venom is 5-6 inch armoured, then there's a good chance German tanks will be likewise (King Tiger has over 7-inches in places?). The capture of some 88mm Flak guns in North Africa will help give the Allies a real knowledge of what they're up against. I think looking a jumping the 95mm towards a 102mm, or better yet, 105mm gun is well worth looking at, even at this point.

The HE capacity of the 17pdr is entirely dependant on the construction of the HE shells. It's theoretical HE capability is higher than any 75mm weapon, though only theoretically in practice. In a tank mounting the set up of the sight is the determining factor for the British. If the Army demands a single reticule sight for both HE and AP then either the AP or HE is going to be limited on both guns. While it is easy to criticise that aspect of British tank doctrine post war I still believe it makes sense from an OTL perspective with a large conscript army. Plus the point @Winged-One made better than me,

the Venom might take the 17pdr first but is ultimately designed to take the larger 94mm.

That would make sense as a starting point. Design the tank to take the gun that is basically ready to go with the capability to be up gunned in future. The Jump from 75mm HV to 95mm/105mm is a lot greater than from 17pdr. Plus Carden likely knows that the 17pdr will be entering production soon so designing the Venom to take the 17pdr means that there will be less or no bottleneck in getting the most powerful gun in service into the tank. The next consideration is if there is a delay in getting the 95/102/105mm gun into service then the Venom still has a very good gun.

 

[Ramp-Rat]

Um, compared to OTL the British are doing massively better, not only did they manage to pull more men out of France (~50K more than OTL), but their victories in Greece (probably several thousand fewer men captured), Crete (probably at least 15K fewer casualties) and North Africa (probably in the region of 200K fewer casualties), leave them probably almost a quarter-million men better off than OTL. Then you add in the 100K+ not captured in Malaya. Add in a few tens of thousands fewer casualties in Burma (if that will even be a thing.

Sir I would dispute your use of the word massively, in regards to the better position ITTL that Britain is in, in comparison to the situation IOTL. Yes Britain is substantial better off now ITTL than she was IOTL, but the major gains will only come after a successful defence of Malaya and Singapore. And while the troops saved as a result of better outcomes in France, the Middle East and the Far East, will provide a significant boost to the British, both morally and materially. The massive boost to the British situation, will only occur after if ITTL America suffers the substantial losses in the Pacific and Philippines, that it did IOTL. If this does occur, then the combination of the better British performance, and it’s continuing ability to export from its Far Eastern colonies, significant quantities of such much needed resources such as rubber, tin and rice. This will be when the British gain a massive advantage in comparison to the state they were in IOTL. While they will eventually be reduced to playing second fiddle in the great/supper power stakes, this will not occur until late 44, as apposed to early 43. And with luck Britain will end the war in a better position than she did IOTL, not as damaged or financially drained, having suffered less casualties than she did.

RR.

 

[MarcH]

...To be honest, there's a decent chance the British might not actually develop a 102mm or 105mm gun as a jump from the 4in/3.7in Carden is thinking about currently; instead of the 105mm L7 being developed from the 84mm 20pdr, the bigger case designed from the basis of the 4in naval gun's case might instead result in being rebored to something like a 4.5in/113mm gun? 84mm to 105mm corresponds closer to 94mm to 113mm compared to 94mm to 105mm, after all. And the bigger calibre will be better for the HESH and HEAT that would be expected to make up a sizeable chunk of the new gun's ammunition load, while sabot instead of AP or APCR basically eliminates the downside of the bigger calibre.

A 115mm gun could be interesting for NATO. That basically negates the 120mm gun currently in use.

17pdr to 102mm to 115 mm would be quite nice for British tanks.

 

[marathag]

...To be honest, there's a decent chance the British might not actually develop a 102mm or 105mm gun as a jump from the 4in/3.7in Carden is thinking about currently; instead of the 105mm L7 being developed from the 84mm 20pdr, the bigger case designed from the basis of the 4in naval gun's case might instead result in being rebored to something like a 4.5in/113mm gun? 84mm to 105mm corresponds closer to 94mm to 113mm compared to 94mm to 105mm, after all. And the bigger calibre will be better for the HESH and HEAT that would be expected to make up a sizeable chunk of the new gun's ammunition load, while sabot instead of AP or APCR basically eliminates the downside of the bigger calibre.

The moster gun the British were working on postwar was L4 gun, 183mm. weighed around 4 tons. based off the old 7.2" gun for caliber
It was to be HESH only, and that shell was around 158 pounds. Tested in the FV4005

 

[Bougnas]

17pdr HE was only an issue on Firefly due to the special mount and breech not allowing it (or good HE). Archer and Challenger had no such issues as they could use the normal gun. Even if they had the fast and weak HE early on, they did get the slower and better version in 1944 at least.

 

[Cryhavoc101]

17pdr HE was only an issue on Firefly due to the special mount and breech not allowing it (or good HE). Archer and Challenger had no such issues as they could use the normal gun. Even if they had the fast and weak HE early on, they did get the slower and better version in 1944 at least.

I also recall that the Firefly could not store the longer 17 pounder HE rounds used on the towed guns (and i assume the Archer and Challenger) due to the ammo racks etc

 

[MattII]

Sir John's indulging in some muddled thinking there - if he wants 45-degree elevation, then his SP howitzer is going to end up with a high, bulky superstructure that for weight reasons can only be lightly armoured. Assault guns, which need heavy armour, are low-profile and don't allow high elevation of the main armament.

I don't know, the Sexton managed 40° and wasn't too bad. A bulky superstructure is only an issue if you want 360° traverse, if you're prepare to accept something with a more limited traverse, you can actually get a half-decent vehicle,

Not really, at least not from the point of view of the current TL. If, as has been suggested, the 75mm HV is comparable or a bit less powerful than the OTL 75mm HV that makes it a bit less powerful than the 77mm HV which was less powerful than the 17pdr. Even without that knowledge and the knowledge of the "accuracy issues" of the 17pdr it is still a notable and worthwhile step up over the 75mm HV.

Not sure muzzle velocity matters a lot to HEAT or HESH.

Sir I would dispute your use of the word massively, in regards to the better position ITTL that Britain is in, in comparison to the situation IOTL. Yes Britain is substantial better off now ITTL than she was IOTL, but the major gains will only come after a successful defence of Malaya and Singapore. And while the troops saved as a result of better outcomes in France, the Middle East and the Far East, will provide a significant boost to the British, both morally and materially. The massive boost to the British situation, will only occur after if ITTL America suffers the substantial losses in the Pacific and Philippines, that it did IOTL. If this does occur, then the combination of the better British performance, and it’s continuing ability to export from its Far Eastern colonies, significant quantities of such much needed resources such as rubber, tin and rice. This will be when the British gain a massive advantage in comparison to the state they were in IOTL. While they will eventually be reduced to playing second fiddle in the great/supper power stakes, this will not occur until late 44, as apposed to early 43. And with luck Britain will end the war in a better position than she did IOTL, not as damaged or financially drained, having suffered less casualties than she did.

Britain is already in the region of a quarter-million men better off, not to mention massive savings in materiel, and Malaya is, even at this early stage, going a ton better than OTL.

 

[marathag]

I don't know, the Sexton managed 40° and wasn't too bad. A bulky superstructure is only an issue if you want 360° traverse, if you're prepare to accept something with a more limited traverse, you can actually get a half-decent vehicle,

The M4 with the 105mm got 35 degrees(same as M7 Priest), and the GMC M37 got to 42.8 degrees

 

[marathag]

Not sure muzzle velocity matters a lot to HEAT or HESH.

faster means better accuracy, but HEAT still needs that stand off distance

 

[MarcH]

Not sure muzzle velocity matters a lot to HEAT or HESH.

It does at this point in time, at least for HEAT. Fuses aren't as good as they would quickly get even pre war, throwing heat too fast and the round impacts and breaks up on the tank before it has had time to go off. Why do you think the 17pdr had no HEAT round developed for it during WW2? Britain was right there pretty much from the beginning with HEAT and the no68 AT rifle Grenade and the PIAT had a very good HEAT round.

 

[MattII]

It does at this point in time, at least for HEAT. Fuses aren't as good as they would quickly get even pre war, throwing heat too fast and the round impacts and breaks up on the tank before it has had time to go off. Why do you think the 17pdr had no HEAT round developed for it during WW2? Britain was right there pretty much from the beginning with HEAT and the no68 AT rifle Grenade and the PIAT had a very good HEAT round.

Therefore, wouldn't a lower muzzle velocity actually be better for HEAT?

 

[MarcH]

Therefore, wouldn't a lower muzzle velocity actually be better for HEAT?

Think we're a bit cross purposes here.

Yes a lower MV would be better for HEAT, thing is for a tank gun in WW2 the velocity will have to be rather low affecting accuracy and range. The QF 95mm Howitzer for instance had a very good heat round at a MV of 1100 ft/s. In WW2 you also run into the issue of needing a larger diameter than 75mm/3" to get a really good HEAT round. See the above 95mm round, the PIAT at 83mm, the Panzerfaust was 100mm minimum and the Panzerschreck's 88mm.

 

[MattII]

Think we're a bit cross purposes here.

Yes a lower MV would be better for HEAT, thing is for a tank gun in WW2 the velocity will have to be rather low affecting accuracy and range. The QF 95mm Howitzer for instance had a very good heat round at a MV of 1100 ft/s. In WW2 you also run into the issue of needing a larger diameter than 75mm/3" to get a really good HEAT round. See the above 95mm round, the PIAT at 83mm, the Panzerfaust was 100mm minimum and the Panzerschreck's 88mm.

The effect of lower muzzle velocity on accuracy is a mixed bag, as that depends on the motion of the target. An approaching enemy won't be affected, beyond perhaps a minor difference in elevation, while one moving laterally will be rather more difficult to hit.

As to ammunition, yes, 75mm isn't ideal, but it does work. Also, most of what the Victors are going to be firing at aren't going to be Panthers/Tigers. Also, what's the size and weight difference between a 75mmHV shell and a 17-pounder one?

 

[marathag]

The effect of lower muzzle velocity on accuracy is a mixed bag, as that depends on the motion of the target. An approaching enemy won't be affected, beyond perhaps a minor difference in elevation, while one moving laterally will be rather more difficult to hit.

lower velocity rounds require for more accurate range estimation. Faster shoots flatter, slower more of a parabolic arc

 

[MattII]

lower velocity rounds require for more accurate range estimation. Faster shoots flatter, slower more of a parabolic arc

And it matters not a jot if you struggle to load the gun properly because the round is too big an awkward to manoeuvre inside the confines of the turret.

 

[sonofpegasus]

The British 4.5" naval gun was relined to take a 3.7" shell in the original 4.5" chamber and shell case. This AA gun had a hi velocity and an effective altitude of around 45K feet.
This is a very big/heavy but effective weapon that exists at this time OTL, ITTL it probably does as well. So what effect does this have of Sir Carden and his plans?

 

[duckie]

The British 4.5" naval gun was relined to take a 3.7" shell in the original 4.5" chamber and shell case. This AA gun had a hi velocity and an effective altitude of around 45K feet.
This is a very big/heavy but effective weapon that exists at this time OTL, ITTL it probably does as well. So what effect does this have of Sir Carden and his plans?

The Brits don't fear the Stalin III and other russian heavy tanks as much as in OTL.

 

[MattII]

The Brits don't fear the Stalin III and other russian heavy tanks as much as in OTL.

You mean the IS-3?

 

[Dathi THorfinnsson]

You mean the IS-3?

Since "IS" stands for "Iosef Stalin", I would assume yes.