A Better 6 pounder

[yulzari]

The tank 6 pounder was always expected to support infantry with HE but the effectiveness of HE is a function of the size of the HE charge which is itself a function of the size of the projectile, thus a larger bore gives a better HE result. Artillery had established before WW1 that 75mm was really the lower worthwhile limit (though horse drawn field guns and mountain guns needed low weights so were often smaller). Hence we saw the efforts in the Mediterranean to fit surplus Sherman 75mm guns into Churchills as the doctrine was that infantry support with HE was the prime role of tanks.

The telling thing is that they retained a proportion of 6 pounders to cope with enemy armour. My hypothesis is that it would only take a small improvement in the anti armour capacity of the 6 pounder for it to do the same in NW Europe, save building Challengers and Fireflies and concentrate on progressing the full 17 pounder tank design into service before the end of 1944.

 

[tomo pauk]

The APDS shot made the 6pdr as capable as feasible, before going into a '6pdr on steroids'? I still maintain that, in second half of 1944, W. Allies have had plenty of 'horizontal' solutions for Panther and heavier; an APDS shot for the US 76mm/3in makes the vehicles equipped as capable for the AT work as the 77mm HV. The '6pdr on steroids' still lacks HE punch, compared with 75mm and heavier, so the British still need a decent HE thrower to deal with targets more numerous than tanks/AFVs.

My hypothesis is that it would only take a small improvement in the anti armour capacity of the 6 pounder for it to do the same in NW Europe, save building Challengers and Fireflies and concentrate on progressing the full 17 pounder tank design into service before the end of 1944.

Doest that mean that Challenger Firefly were not to be designed/built?

Hi, Jabberwocky,

17 pounder had an in-action weight of 4,624 lbs, at least according to the Royal Artillery. That's just under 50% more than the Pak40 7.5 cm, which had an in-action weight of about 3,135 lbs.

Would that be with the carriage of the 25pdr, or with split carriage? If it would not be much of a trouble for you, perhaps you could direct me towards an easily obtainable source that gives the figure; the 3 books I've have all state the weight in cation at circa 6400 lbs.

The problem with fitting the 17 pounder into UK manufactured tanks is that UK tanks had turret rings that were too narrow, primarily due to the narrow UK rail gauge and the loading gauge (and thus the width of rail tunnels). The UK War Office change the loading gauge design limitation from 8'9" to 9'6" in 1941 (to accommodate the Churchill) and then dropped the requirement altogether in 1942.

It was too unfortunate that, after Matilda II, no British ww2 tank (worth speaking of) was not featuring sponsons.

The main problem with the QF 6 pounder is the lack of effective HE, which was more a doctrine issue (in the UK) than an design issue. I believe (but I could be way out on this one) that HE ammunition was first issued for UK guns in March or May 1944, but ammunition was in relatively short supply. HE was used in late 1944 and through 1945 by 6 and 17 pounders for bunker/ hardened emplacement plinking at long-ranges, outside of MG ranges.

Perhaps you could kindly shed some light at the question: why the HE shells were not issued to the guns prior 1944?

 

[Shortround6]

The 6pdr went from (roughly) 74mm of penetration at 500yds/30^ to 84-88mm of penetration by going from the interim 43 caliber caliber barrel to the originally planned 50 caliber barrel and changing from APC to ABCBC shot. this later shot improved things even more at longer ranges as it was more streamlined and keep it's velocity better. British ammo was loaded to pretty high pressures to begin with so not much scope is left there.
The British should have gotten the stick out and made a tank to use the 77mm or whatever you want to call it earlier. It used a hot loaded 3in AA case so the case and chamber were no great mystery. Just chamber up a modern barrel with enough chamber wall. pick your projectiles (75mm or 76.2 mm) and go to it. Futzing about with a "super" 6pdr is just going to delay the inevitable, a proper 75-77mm weapon.

 

[tomo pauk]

Futzing about with a "super" 6pdr is just going to delay the inevitable, a proper 75-77mm weapon.

That wraps it up.

 

[yulzari]

But the 'proper 75mm-77mm' was half a failure to fit the Cromwell and half a failure to get it into service with Comet except just in the last few weeks in small numbers.

By skipping this stage, when it was found impossible to use the 75mmHV in time in 1942, the real 17 pounder vehicle might have been in service in numbers in late 1944 while the 6 pounder held the fort in the meantime..

If we go back to 1941 and ensure the Cromwell would take the 75mmHV well and good; but my starting point is what action to take when it was found that the 75mmHV would not fit the Cromwell and that was too late to enlarge the turret.

Not how to get the 17 pounder 77mm in tank service for D day. That is easy. Just wave a wand and say that the Ministry of Defence ordered such a weapon and tank in 1936. Job done. There was no novel technology in the Comet bar the APDS. The Centuar and Cavalier worked with Liberty engines. There were a variety of workable gearbox types to use and insisting on welding armour would have been easier as there was less competition then for the supply of suitable welding kit.

The various suggestions that the 17 pounder and/or 77mm should have been used earlier is perhaps somewhat like responding to a question of whether the RAF should have had just more Spitfires instead of maintaining Hurricane production for the Battle of Britain by saying they should have got the Typhoon in service in 1939. The Hurricane was already showing obsolescence in 1940 but it was useable and existed.Yes the Typhoon was far better and the desired replacement but it was not possible to produce it for 1940. The 6 pounder is the Hurricane equivalent. Good enough but not good. It existed in quantity. The 77mm is the Hurricane MkII/IV. Not the best, just a bit better and built only because the replacement had problems. This is an analogy and like all analogies, they are to illustrate a point and attacking the analogy does not destroy the original premise.

Now if someone can convince me that the 6 pounder was unable to take on the task (and, yes, if i were the tankie I would want a 17 pounder or at least a 77mmHV) then I would conclude my hypothesis was incorrect.

For the unwary, the 3" AA gun itself was far too heavy too large and could not take 77mm pressures as I am sure Shortround6 would be happy to confirm.

 

[Juha]

Now if someone can convince me that the 6 pounder was unable to take on the task (and, yes, if i were the tankie I would want a 17 pounder or at least a 77mmHV) then I would conclude my hypothesis was incorrect.

If you read the history of 6th Guard Tank Brigade, you would find out that men of the brigade thought that 6pdr even with APDS wasn't adequate against frontal armour of Panther/Jagdpanther

For the unwary, the 3" AA gun itself was far too heavy too large and could not take 77mm pressures as I am sure Shortround6 would be happy to confirm.

As I wrote 75mm/76.2mm Vickers Model 1931 AA gun would have given almost as good penetration power as the German 7,5cm Pak 40 plus ability to fire reasonable good HE early in the war, it would not have been reliable Tiger killer frontally, but that would have been a problem only from Nov 42 onward. And as SP A/T gun like Archer or German Marder,so not as a tank gun, but something on tracks with long range killing ability against panzers and Paks.

Juha

 

[Shortround6]

But the 'proper 75mm-77mm' was half a failure to fit the Cromwell and half a failure to get it into service with Comet except just in the last few weeks in small numbers.

By skipping this stage, when it was found impossible to use the 75mmHV in time in 1942, the real 17 pounder vehicle might have been in service in numbers in late 1944 while the 6 pounder held the fort in the meantime..

If we go back to 1941 and ensure the Cromwell would take the 75mmHV well and good; but my starting point is what action to take when it was found that the 75mmHV would not fit the Cromwell and that was too late to enlarge the turret.

Now if someone can convince me that the 6 pounder was unable to take on the task (and, yes, if i were the tankie I would want a 17 pounder or at least a 77mmHV) then I would conclude my hypothesis was incorrect.

The question is how do you improve on the existing 6pdr to meet your goal, which you have haven't specified unless I missed it. what are you looking for 92mm penetration at 500yds/30 degrees or 100mm or 110mm?

The 6pdr was designed with the 50 cal length barrel and only made with the 43 cal barrel as production expedient due to a shortage of lathes to make the longer barrels. Increasing the length to 55 calibers or longer is going to give very little return without changing the powder charge. The 6 pdr was already operating at the top of the range of chamber pressures. If they could have used a different propellant that gave a higher velocity they probably would have. The Navy was able to use different propellants that gave longer barrel life because they gave the about the same pressures with a lower flame temperature but they rarely, if ever, increased the velocity.

This pretty much leaves reaming out the chamber to take a larger cartridge case with more volume and a larger charge to generate more gas at the same peak pressure. Now we are back to trying to figure out if the new case will fit the old barrel or will the chamber walls be too thin, will the new case fit the breech block. Will the breech block take the strain. as an example changing from a 90mm diameter case to a 100 mm diameter case increases the forces acting on the breech block by over 23% even at the same chamber pressure. Maybe the answer to all these questions is "no problem" and it is an easy change, but if the answer starts coming back as bulged barrels, or breech blocks setting back or other problems then what?

 

[Shortround6]

As I wrote 75mm/76.2mm Vickers Model 1931 AA gun would have given almost as good penetration power as the German 7,5cm Pak 40 plus ability to fire reasonable good HE early in the war, it would not have been reliable Tiger killer frontally, but that would have been a problem only from Nov 42 onward. And as SP A/T gun like Archer or German Marder,so not as a tank gun, but something on tracks with long range killing ability against panzers and Paks.

Juha

The 75mm/76.2mm Vickers Model 1931 AA was not that great an improvement on the 3in 20cwt gun if the Wiki figures are to be believed. 2500fps with a 14lb shell? the old 3in 20cwt gun could manage 2040fps with a 17.5lb shell and up to 2500fps with a 12.5lb shell. increasing shell weight by 12% while keeping the same velocity is nice but not exactly a major leap forward.

 

[Juha]

The 75mm/76.2mm Vickers Model 1931 AA was not that great an improvement on the 3in 20cwt gun if the Wiki figures are to be believed. 2500fps with a 14lb shell? the old 3in 20cwt gun could manage 2040fps with a 17.5lb shell and up to 2500fps with a 12.5lb shell. increasing shell weight by 12% while keeping the same velocity is nice but not exactly a major leap forward.

Yes, but Model 1931 was significantly lighter, 3,325/2,825kg, the later is in action weight, 3in 20cwt weighted 5,99 tons according to wiki.

Juha

 

[fastmongrel]

I think the only way your going to get bigger guns in British tanks earlier is if you specify that all interwar and therefore early war tanks had to carry the WWI Hotchkiss type (40 cal I think?) 6 pounder. This would force British designers to use larger turret rings from the start as the Hotchkiss 6 pounder is a good sized lump. Going to the much smaller 47mm 3 pounder then the slightly smaller again 2 pounder allowed small turret rings to be used.

 

[Jabberwocky]

Hi, Jabberwocky,

Would that be with the carriage of the 25pdr, or with split carriage? If it would not be much of a trouble for you, perhaps you could direct me towards an easily obtainable source that gives the figure; the 3 books I've have all state the weight in cation at circa 6400 lbs.

That's from the 1943 QF 17-pr handbook with the Mk I (split-trail) carriage. There is also a figure of 2 tons 17cwt 1qr 25lbs in the handbook - which equals 6540 lbs - as travel weight, but it doesn't specify what type of carriage.

Most confusing. There seems to be some contradiction in both the handbooks and specialist literature. I have weights of the gun in action ranging from 4,001 lbs (!) all the way up to 6600 lbs in various books, with travel weights as high as 6900 lbs.

Zaloga's US anti-tank artillery book also gives the 4624 lbs figure when comparing the 17 pdr with the US 3 inch.
Delf's book on UK anti-tank artillery gives the weight as 6537 lbs, but then clouds the issue
by referring to the weight of the gun as "over 4,000lb" when referring to crews moving it.

One of the other problems is that the British made a number of modifications to the carriage, adding more armour and substantially adjusting the recoil mechanism. There were at least three different 'Mk I' carriages, as well as a Mk Iw.

I'll do some more digging, but I'm beginning to wonder if the lower end figures aren't for the gun/carriage as is, while the upper weights are for the gun, carriage, spares and possibly ammunition. Maybe AVIA 46/187 or the later 17-pdr handbooks can clear this up.

 

[tomo pauk]

Much appreciated, I'm hoping that the matter will be cleared

Brits have found the way to mount a turret featuring the 20pdr cannon (84 mm L.64) at the Cromwell hulls, creating the Charioteer TD. Price paid was that turret was bulkier and of thinner armor. Looking at the pictures, the 20pdr, due to higher line of fire, recoiled into the space that, in Cromwell's turret, was occupied be the radio set. The mantlet was somewhat in the front, at least it seems to me by looking at the pics. So I'd say they circumvented the narrow hull ring limitation.
Too bad that they did not mounted the 75mm HV, or 77mm HV into the Cromwell, using the outer mantlet and/or higher line of fire. Ditto for Comet/17pdr. The price would be the weight gain (for same protection level), no doubt about that.

 

[Juha]

Ah
Charioteer mentioned, have ridden on one during a military exercise looong time ago, not the one in the attachment.

Juha

 

[tomo pauk]

Great; my only 1st hand experience with 'tanks' was anti-tank drill vs. and ZSU-57 playing a tank (turret covered with canvas for the occasion), and I've been several times within the turret of the M-47 (48?) Patton. US-made tanks were being mothballed at the barracks I was serving 1990/91, Ljubljana - Slovenia.

How well the Charioteer was regarded in the Finish army?

 

[Juha]

Now what I remember
it was fast and the gunner's sight was very good but the commander was fairly blind when buttoned up. The Finnish Charioteers had a mg, it was the type as used in T-34s IIRC. The cannon was very good. IIRC Army wasn't altogether satisfied because of light armour of the turret and because of the limited observation possibilities for the commander.

Juha

 

[Juha]

My experience was also after we had "stopped" a tank attack during an exercise, after that we got a couple km ride on one Charioteer on road and off-road. Later I spent some time in the turret of one, which was camo'd in an A/T position for possible war use, at that time I noticed how good the gunner's sight was. And in 60s and 70s one could freely climb into the turrets of Pz IV, T-28, KV-1 etc at Parola Tank Museum.
Juha

And the Charioteer at Parola

 

[Shortround6]

Thank you for the pictures. They also show a few considerations of turret design. The Comet shows how elevation limits can affect turret ring size. At high angles of elevation the gun needs room to recoil ( and needs room behind it to load) and also look at the roof line. At large angles of depression the gun still needs room to recoil and be loaded. The range of elevation of the Comet was from +20 degrees to -10 degrees. The Charioteer had an elevation range of +12 degrees to -5 degrees even with the larger turret.

 

[Juha]

Thank you for the pictures. They also show a few considerations of turret design. The Comet shows how elevation limits can affect turret ring size. At high angles of elevation the gun needs room to recoil ( and needs room behind it to load) and also look at the roof line. At large angles of depression the gun still needs room to recoil and be loaded. The range of elevation of the Comet was from +20 degrees to -10 degrees. The Charioteer had an elevation range of +12 degrees to -5 degrees even with the larger turret.

Yes, Charioteer wasn't perfect, IMHO not even optimal solution, but definitely more effective A/T system in 50s than Cromwell, and British (and Finns) needed A/T system that was effective frontally against T-54s/T-55s, so IMHO some failings were acceptable if the main point, mobile hard-hitting A/T system could be produced fairly cheaply and fast. In certain respects Charioteer was a bit like M-18 Hellcat.

Juha

BTW, I made a mistake earlier, in Charioteer commander was also gunner and the other man in the turret was loader/radio operator.

 

[tomo pauk]

Charioteer is to the Cromwell what is the M-36 to the M4s. What was the disposition of the rest of the crew in the Charioteer?

 

[Juha]

In principle it had a 3 men crew and the 3rd one was the driver, but because of the high muzzle pressure dirt made the observation of hits difficult when target was under 1500m away, so sometimes 4th man was carried in the place of Cromwell's hull gunner, he when readied for action would have moved to commander/gunner seat allowing the commander to move out of tank and 10-30m sideways, so that he would have been able to observe the fall of the shot and give if necessary corrections to the acting gunner/4th man.

Juha