A Better 6 pounder

[yulzari]

The 57mm 6 pounder anti tank gun/ tank gun was used widely by British, Commonwealth and US Forces in WW2.

Given the extraordinary lengths the British went to squeeze the 17 pounder into a tank turret could the 6 pounder have more performance squeezed out of it?

A longer barrel to go with APDS like the Italian high velocity 60mm that went into the last operational Sherman gun tanks perhaps?

 

[Shortround6]

The British originally planed a 50 caliber barrel but a shortage of lathes with long enough beds force the production of the 43 caliber length barrels for a while. While a longer barrel would have squeezed out a bit more performance I believe the Italian/Israeli high velocity 60mm used an even bigger cartridge case to get it's performance. Possible in WW II but it also means fewer rounds per tank in the storage racks and a shorter barrel life.

 

[tomo pauk]

The longer barrel can give only so much a performance growth. The Germans used different rounds for 'mid power' 7,5cm (L43/46/78; even the L46 using different round vs. other two?) vs. the 'hi-power' 7,5cm L70, the 8,8cm L56 and L71 were also firing different rounds, same for 5cm L42 and L60 - just to give some perspective.
Mounting the 6 pdr as-is into tanks in 1941-42 would give far more boost for UK Commonwealth tank forces, for AT work, let alone the 'soft' attack; not the topic here, though.

 

[yulzari]

The advantage of retaining the 6 pounder is that it fitted the existing turrets and chassis.

One can tweak the ammunition as well as the gun. With a longer barrel you will need to alter the burning charge and characteristics to maintain the projectile's acceleration down the extra barrel length. Not a great increase, but combined with APDS it makes it just that bit nearer 77mm penetration if not full 17 pounder penetration. A muzzle brake would mitigate greater forces on the existing mountings though the greater barrel weight would alter the balance of the gun.

So British and Commonwealth tanks can stay effective until the end of the war using 6 pounder tanks to support 75mm ROF tanks, much as 6 pounders were used in Italy and as Fireflies were to support Shermans in NW Europe. Saving all the effort into squeezing the 17 pounder into something. The 17 pounder needed to go into a 17 pounder tank and that was the Centurion, so skipping the Comet.

 

[davebender]

Most army targets are soft targets. HE filler amount is mostly related to shell size. So I cannot see much point trying to give the 6 pounder cannon even more velocity. Britain would be further ahead using the 6 pounder as is and spending development money trying to build something similiar to the German 7.5cm Pak40.

The 17 pounder cannon is not the answer. It weighs twice as much as a Pak40 which made it a clumsy AT gun and it would not easily fit in a tank turret. Consequently the British army had to develop the 77mm HV cannon for their new Comet tank. Perhaps Britain could develop the 77mm HV cannon and skip the 17 pounder entirely.

 

[Shortround6]

The 17pdr had the performance of the 75mm/L70 in the Panther tank which put it in a rather different class than the Pak40. The Panther gun also weighed about twice as much as the 75mm/L43-46-48 series of guns. Perhaps the Germans should had skipped the 75mm/L70 ?

 

[davebender]

Germany had priorities right. They developed the Pak40 first and it served as their main tank / AT / assault artillery cannon during 1942 to 1945. The Panther cannon was developed later and was never used as a towed AT gun.

 

[Shortround6]

First lets a fact or two straight. The 17pdr did not weigh twice what a Pak 40 did, it weighed about 50% more. It also weighed a whole lot less than than all the rest of the heavy AT guns the Germans dragged onto the battle field, like all those 88mm guns. Like the 75mm/L70 the 17pdr could out penetrate the 88mm/L56 at most normal combat ranges.
The British 6pdr could have been looked at the Germans for a few hints also. When loaded with the same type of projectile as the PaK40 (APCBC) it wasn't that far behind in penetration.

 

[yulzari]

My objective was to examine if British industry could have saved themselves the time and cost of trying to fit a 17 pounder into some modification of existing tanks by upgrading the 6 pounder as an anti tank weapon. As in Italy I would presume the majority of tanks would use the ROF 75mm as their principal job is to use HE to support infantry, retaining a proportion of (upgraded) 6 pounder tanks for protection.

Industry could then be devoting it's time and resources into a proper (ie Centurion) 17 pounder tank in full service for a year earlier and no need for the 77mm at all.

 

[tomo pauk]

17 pdr was needed to reliably defeat the Panther and heavier stuff. British had one modification of the existing tank that cost them almost nothing, that being Sherman Firefly. It was feasible in 1943, too bad it was not present in far greater numbers from winter 1943/44, especially in Normandy.
For something of lower power, the derivative of the 3in AAA cannon was a choice, materialized as the 77mm cannon. Unfortunately, it was too late, too few; one wonders if the Cromwell might have carried it?* With APDS, the 'animals' are within the scope.
Further down, the 75mm with APDS might be a nasty surprise for an unsuspecting Panther's or Tiger's crew. And one still gets good HE performance, with shell being of modest size (= more to be carried, vs. the bigger two).
Sorry if it sounds like I'm raining into your parade, just think that Brits have had more tempting options, as far as tank armament is in question. The British tank development (for tanks used in ww2) received plenty of the bad rap. I can agree with much of it.

*will try to compare the layouts of Cromwell, T-34-76 T-34-85; the 77mm should need turret of the size in-between of the later two, or maybe as big as for T-34-76, if the muzzle brake is carried?

 

[davebender]

British had one modification of the existing tank that cost them almost nothing, that being Sherman Firefly.

Have you looked at the amount of craft work required to convert a Sherman tank into a Sherman Firefly? I am unable to find a historical price but I suspect the conversion cost as much as the original tank.

 

[tomo pauk]

Yes, I did.
Brits have deleted the hull gun, using the place now vacant (no hull gunner) for ammo stowage. The stowage box was relocated at the front of the hull, they welded the armored box for radio at the back of the turret, radio being accessed through the hole cut in the rear turret wall. The main modification was the new cannon, installation being simplified through usage of existing trunnions (of the 75mm cannon installation).
Seems like a far simpler modification than Cromwell -> Challenger, of Churchill -> Black Prince. Hull remained the same (bar the 'patching' the hull, where the MG was), while the turret was a non-fancy modification of the one that was shipped from the USA.

 

[Shortround6]

Tanks and tank cannon ( and ammunition ) are a lot like aircraft. It take several years for a program to go from drawing board to service use. A good planner is never trying to match what his enemy just put into the field but what he thinks his enemy will put into the field in 2-3 years. The British spent several years behind the curve due to decisions made in 1937-40 and then stalled as they tried to make up for the losses in France. At some point they decided to get to the front of tank/anti-tank armament, instead of being in 3rd place, and stay there. Stopping the 17pdr to go ONLY with the 77mm would have dropped them back in the race. While APDS turned out to work very well, it was by no means a sure thing even in 1944 and the results of firing trials with bad batches of ammo and lack of accuracy with early ammo types only emphasize that relying on trick ammo instead of the developing bigger guns would have been foolish.
Even the US with comparative lack of raw material supply problems was only getting enough APCR shot to it's tanks and tank destroyers with 3in/76mm in the fall/winter of 1944 to supply them with 2-5 rounds apiece at a time. This is a big hang up with the APCR 75mm for Shermans that is brought up so often. Every 75mm round with tungsten is one 76mm with tungsten NOT made. Which round is going to give the American tankers the best chance to take out a big German tank?
A Low chance hit from the 75( even if better than the normal 75AP) or a higher chance hit from the 3in or 76mm guns?

Many of these tank, gun and ammo programs overlapped considerably in timing.

Considering that the Germans fielded not only the 88mm DP guns, but dedicated 88 mm Anti-tank guns AND 128mm anti-tank and tank guns I don't see how the British can be faulted for fielding the 17pdr.

The Germans may have done better to field the 75mm/L70 as an AT gun than trying to Feild those ultra heavy monsters.

 

[tomo pauk]

I don't think that anyone is trying to blame the British for fielding the 17pdr. It took a while to come out with the suitable platform, though. A quote from T. Williams' site is quite telling (all quotes are from the expert):

The Vickers 75mm HV was supposed to fit in the new Cromwell tank, but it was discovered rather late in the day that the Cromwell's turret was too small, causing a major crisis.

...the 75mm HV being a derivative of the AA 3in cannon, lined down to accept the US 75mm shells/projectiles. So Cromwell (as-is) is out of game :\
This is very interesting, about the cannon:

The M61 [APCBC projectile]weighed 6.77 kg and was fired at 808 m/s from the Vickers HV for a muzzle energy of 2,200 kJ, compared with 620 m/s from the US tank guns (1,300 kJ). As a result, penetration went up from about 60mm to an estimated 87mm - not a huge amount more than the 6 pdr 7 cwt, but with a vastly more effective HE shell. The M48 [HE round] was downloaded to only 457 m/s since the thin-walled shell could not take the same high chamber pressures as the M61.
(the 76mm M42 HE shell contained only 390g TNT compared with 667g for the 75mm M48)

...meaning the HE round was notably better for the 75mm HV. It was also better than of the 17pdr, HE round featured the thick-walled shell there. 17pdr is far better AP thing, unsurprisingly.
The 75mm HV was further modified into the 77mm:

Meanwhile, Vickers persevered with their 75mm HV and the next tank, the Comet, was designed around it to make certain that it would fit this time! Before it could enter service, it was decided to take the calibre back up to the original 76.2mm so that the new gun could use the same projectiles as the 17 pdr, and the gun was then renamed the 77mm (presumably to distinguish it from the US 76mm).

the 77mm with this ammo [APDS] could penetrate 165mm [range not stated, 100 yds maybe?]

As for German AT guns heavier than the 'regular' 7,5cm pak, all of them were requiring the good vehicle to tow them. Going for the SP version makes far more sense to me.

 

[yulzari]

The 77mm is a version of the Vickers 75mm HV that was intended to be the Cromwell's normal gun. Due to some **** up in coordination they then found it wouldn't fit! Hence the panic to try to get a 17 pounder into something. The Comet was designed around the 75mmHV that used the 3" AA case but reverted to the 3" (76.2mm) bore but was termed 77mm to avoid confusion with other 76mm rounds.

The external mantlet of the Sherman left less 17 pounder protruding into the turret than in a Cromwell/Churchill type of turret with an internal mantlet. Even then it had to be mounted on it's side and substantially modified. Put one in a Cromwell and the breech hits the turret rear if it fired. The good news is that it would have too little room left in the turret to load a 17 pounder round anyway.....

I heard a (very) dubious story that someone at the time asked if a 17 pounder could be put into a Grant as there was more room inside, the turret be removed and additional armour added.

The 17 pounder was a next generation tank gun and really demanded a next generation tank (Centurion). The 77mm,, nee 75mmHV, was the intended 1943/4 intermediate gun. In it's absence, and in the knowledge that a 6 pounder APDS was a viable (if not ideal) anti tank gun, I wondered if it could fill the gap with a little tweaking.

If the Vickers 75mmHV had fitted then the Cromwell (and presumably Churchill) would have been quite formidable machines in 1944.

 

[Shortround6]

I don't think that anyone is trying to blame the British for fielding the 17pdr.

It is not you but somebody on this thread is trying to make out like it was a mistake.

As for German AT guns heavier than the 'regular' 7,5cm pak, all of them were requiring the good vehicle to tow them. Going for the SP version makes far more sense to me.

Very true, once you are above the size of the 50mm Pak or perhaps the 6pdr manhandling the guns any distance beyond a few hundred yds is impractical. However towed guns are cheap. A towed gun may cost 10% of what the similar gun in a tank would cost and trucks are no where near as expensive as any sort of track laying vehicle.

 

[tomo pauk]

The 77mm is a version of the Vickers 75mm HV that was intended to be the Cromwell's normal gun. Due to some **** up in coordination they then found it wouldn't fit! Hence the panic to try to get a 17 pounder into something. The Comet was designed around the 75mmHV that used the 3" AA case but reverted to the 3" (76.2mm) bore but was termed 77mm to avoid confusion with other 76mm rounds.

The 17 pounder was a next generation tank gun and really demanded a next generation tank (Centurion). The 77mm,, nee 75mmHV, was the intended 1943/4 intermediate gun. In it's absence, and in the knowledge that a 6 pounder APDS was a viable (if not ideal) anti tank gun, I wondered if it could fill the gap with a little tweaking.

If the Vickers 75mmHV had fitted then the Cromwell (and presumably Churchill) would have been quite formidable machines in 1944.

Designing a whole new tank in order to properly* accept a modestly sized gun is really out of whack. 'Properly' meaning a rotating turret for the gun, 3 crew members in turret, coax with plenty of ammo, plenty of main gun ammo...
Agreed on 75mm HV for Cromwell/Churchill, it would've given the Germans a good ride for their money. In lieu of that, the APDS for 75mm is again my favorite

The external mantlet of the Sherman left less 17 pounder protruding into the turret than in a Cromwell/Churchill type of turret with an internal mantlet. Even then it had to be mounted on it's side and substantially modified. Put one in a Cromwell and the breech hits the turret rear if it fired. The good news is that it would have too little room left in the turret to load a 17 pounder round anyway.....

Yep, the Comet/Cromwell look like having a gun 'inside' the tank, while the Sherman looks like the gun is 'outside' of the tank.

I heard a (very) dubious story that someone at the time asked if a 17 pounder could be put into a Grant as there was more room inside, the turret be removed and additional armour added.

The Grant + 17 pdr (or even the US 76mm; all minus the 37mm turret) fits somewhere between StuG-IIIG and JagdPanther, a most tempting combination.

It is not you but somebody on this thread is trying to make out like it was a mistake.

Roger that.

Very true, once you are above the size of the 50mm Pak or perhaps the 6pdr manhandling the guns any distance beyond a few hundred yds is impractical. However towed guns are cheap. A towed gun may cost 10% of what the similar gun in a tank would cost and trucks are no where near as expensive as any sort of track laying vehicle.

The SP guns need far less crew to operate an ATG (and other artillery) efficiently vs. their towed counterparts. So a trade off between fewer manpower and more expensive hardware? At the time we arrive at 8,8cm PaK, let alone the 12,8cm (and their Soviet equivalents), the prime mover required for those is not cheap anymore. Maybe the 17pdr, 85mm D-44 and (unbuilt) 7,5cm L70 PaK would be the heaviest cannons able to be 'cheaply' towed, including off-road towing?
Sure enough, a truck-borne 7cm+ SP ATG would be interesting; Italians were experimenting with such a vehicle (along with SP AAA 90mm).

 

[Shortround6]

SP guns do need less crew but what is often over looked is that SP guns often had a lower rate of fire, a lower rate of engagement, in some cases limited traverse, and in most all cases except for the big German guns ( or AA guns), harder to hide.

The loader on a towed gun stood, or knelt, by the breech and his job was to shove a shell into th breech whenever the gun fired and the breech opened itself. There was another crewman, or a chain of them, reaching to the ammo supply, who slapped a fresh shell into the hands of the loader. The SP gun loader had to get the rounds out of the rack/s, orientate them and then do the loading. The towed gun's gun captain could be a few yards to one side or the other of the gun for a better view, especially after the gun kicked up a cloud of dust or dirt. Perhaps the SP gun commander could dismount? This tactic was used by a few SP guns.
Again, in different circumstances, different weapon proved better than the other but often, not in all circumstances.

And yes, when your towed guns start to get in the 5-10 class, their tow vehicles tend to get specialized and expensive.

 

[tomo pauk]

Good post; the limited ability to hide/camouflage being maybe the major shortcoming of the SP vs. a towed variety. As for the kicked dust, the higher line of fire should make that a less of an incident for a SP variant, so the firing position is less likely to be revealed?

(yulzari, if you think the thread is going way off topic, just let me know and I'll reduce the non-6pdr posting)

I'd like to return to the 75mm ('plain', not HV) + APDS.
For comparison sake, the penetration of the 77mm HV went up some 50% when firing APDS vs. the results of the APCBC. The APDS shot being 45% of the APCBC shot's weight. The penetration of the 6pdr grew similarly, APDS vs. APCBC. Under same token, the penetration of the 75mm gun, with APDS replacing the other AP shots should rise for 50%. Or perhaps only 40%, just to be on the safe side. The data found on the 'net suggest that 75mm was able (at 30 deg from normal) to pierce 58-75mm at 500m, and 45-70 mm at 1000m.
Add 40%, and 85-110 mm can be defeated at 500m, 65-100mm at 1000m. All at 30 deg - the Panther is a fair game here. At 0 deg, penetration is at higher numbers of the interval - the Tiger's sides can be penetrated under 1000m, front under 500m. The quirk is that German drivers can drive the tank, terrain permitting, at 30-60 deg (plus 90/180/270 deg) vs. the gun that is about to fire at him. Well, better bring the 17pdr - now you know what a 'reliable penetration' menans

About this:

the 77mm with this ammo [APDS] could penetrate 165mm [range not stated, 100 yds maybe?]

It's 1000 yards

 

[yulzari]

Going off topic is part of the charm of the forum but it would be nice if someone could contribute to the question of improving the 6 pounder rather than what they would prefer to have instead. I would prefer the 17 pounder but it wasn't going to fit anything in 1943/4 British production.

The 6 pounder did fit and was a better AP gun than it's bored out 75mm companion using a WW1 French field gun case. In the Western Desert the AP shortfall of the Grant's American 75mm was known and they took captured German 75mm projectiles and fitted them into captured French 75mm cases. Now if the Grants had been captured too the whole thing would have been free. Yes I do know the great thing about the Grant was that it could take out antitank guns at range with HE.