WW2 British tank gun questions

monochromelody

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I have some questions about WW2 era British tank guns and hope that you can help.

1. In the early stage of TOG 2 tank, they planned to install a 3in 20cwt gun or a 3.7in AA gun Mk.I (also known as 3.7in monobloc or 28pdr) into the turret. But later they developed the 17pdr, some sources say that 17pdr has a 3.7in monobloc chamber.
Considering that there were ideas about necked down 3in 20cwt to fire a Sherman 75mm shot(75mm 50 calibre HV), is that means they also necked down the 3.7in to fire a new 3in shot, which known as 17pdr?

2. Comet tank, armed with a 77HV gun, said to have a shorten 17pdr barrel with a 3in 20cwt chamber. Is that means 77HV can fire original 3in 20cwt HE shells? It's also said that 77HV have better accuracy firing HE shells than those firing from a 17pdr.

3. A39 Tortoise assault tank, armed with a 94mm 32pdr AT gun, greatly differed from a 3.7in AA gun, with a rim diameter of 142mm and a case length of 909mm. I assumed it was developed from a known chamber or case design, for example a 4in Mk.V naval gun/coastal gun, which had a 141mm rim diameter and a 730mm case length. I mean if you stretch the case to 909mm, it will just fit to 94mm calibre.
59fe7c95c8ee037d.png
Is there any info about how 32pdr AT was developed?
 

DWG

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I have some questions about WW2 era British tank guns and hope that you can help.

1. In the early stage of TOG 2 tank, they planned to install a 3in 20cwt gun or a 3.7in AA gun Mk.I (also known as 3.7in monobloc or 28pdr) into the turret. But later they developed the 17pdr, some sources say that 17pdr has a 3.7in monobloc chamber.

I don't think I've seen the '3.7" Monobloc' designation before, so if it was used it may not have been used widely. I do wonder if the 'monobloc' refers to the barrel construction rather than the chamber.

WRT whether the 17 Pdr used the 3.7" AA chamber, the 3.7" AA Mk 1-3 casing was 94 x 675R, while the 17 Pdr was 76.2 x 585R, 90mm shorter. Using the 3.7" chamber dimensions might have been possible - I don't think you could use it unmodified given you need a smaller throat leading into the smaller barrel - but 3.54" of extra steel seems unnecessarily wasteful, at a time when steel was in short supply, as well as making the gun less suitable for use in a turret.

(Edited to change references to the casing to Mks 1 to 3, Mks 4 and 5 used the same casing as the Mk 6)
 
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Old_ROF

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Copy of links to information/ discussion. May be of interest.

British Ordnance Collectors Network forum

Tony Williams site.

Tortoise tank info
 

Tony Williams

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I have some questions about WW2 era British tank guns and hope that you can help.

1. In the early stage of TOG 2 tank, they planned to install a 3in 20cwt gun or a 3.7in AA gun Mk.I (also known as 3.7in monobloc or 28pdr) into the turret. But later they developed the 17pdr, some sources say that 17pdr has a 3.7in monobloc chamber.
Considering that there were ideas about necked down 3in 20cwt to fire a Sherman 75mm shot(75mm 50 calibre HV), is that means they also necked down the 3.7in to fire a new 3in shot, which known as 17pdr?

2. Comet tank, armed with a 77HV gun, said to have a shorten 17pdr barrel with a 3in 20cwt chamber. Is that means 77HV can fire original 3in 20cwt HE shells? It's also said that 77HV have better accuracy firing HE shells than those firing from a 17pdr.

3. A39 Tortoise assault tank, armed with a 94mm 32pdr AT gun, greatly differed from a 3.7in AA gun, with a rim diameter of 142mm and a case length of 909mm. I assumed it was developed from a known chamber or case design, for example a 4in Mk.V naval gun/coastal gun, which had a 141mm rim diameter and a 730mm case length. I mean if you stretch the case to 909mm, it will just fit to 94mm calibre.
A few comments, as the subject of the development of these medium calibre (75-94mm) high velocity guns in WW2 interests me.

The ammunition development is the most important element, and the key measure is the cartridge case rim diameter: case length and calibre can be changed relatively easily, but the rim diameter is fixed for any particular gun design.

There might have been a relationship between the 3.7 inch Mk I-III and the 17 pdr, as both cases used 135mm rim diameters. This raises an interesting question: given that most tank ammo seems to have been expended against soft targets (artillery, buildings, unarmored or lightly armoured vehicles, troops in the open etc) for which HE shells are considerably more destructive than AP shot, might the 17pdr tank gun have been replaced with a larger calibre version with a more effective shell? Either the 3.7 inch (94mm) AA gun or an intermediate calibre such as 87mm - as used by the 25 pdr. Such a cartridge would actually have been more powerful than the German 88mm L/56 as used by the Tiger 1, but the gun need have been no bigger than the 17 pdr.
 

DWG

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The mention of 'OQF 3.7" Monobloc' there could definitely be referring to the barrel. In fact looking up the wiki entry for the 3.7" AA it specifies "Monobloc barrel" as the distinguishing feature of the Mk 1, while later Marks are specified as built-up guns with liners, Mks 4-6 using the 4.5" AA barrel with a 113mm rim diameter cartridge.
 

Tony Williams

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The mention of 'OQF 3.7" Monobloc' there could definitely be referring to the barrel. In fact looking up the wiki entry for the 3.7" AA it specifies "Monobloc barrel" as the distinguishing feature of the Mk 1, while later Marks are specified as built-up guns with liners, Mks 4-6 using the 4.5" AA barrel with a 113mm rim diameter cartridge.
The very high-velocity 3.7 inch Mk VI fired 94 x 857R mm ammunition with a 150mm rim.
The WW2+ 4.5 inch naval/AA guns using fixed ammunition fired 114 x 695R mm ammunition with a 167mm rim.
 

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The very high-velocity 3.7 inch Mk VI fired 94 x 857R mm ammunition with a 150mm rim.
The WW2+ 4.5 inch naval/AA guns using fixed ammunition fired 114 x 695R mm ammunition with a 167mm rim.

Definitely not going to argue cartridge dimensions with an expert, but worth noting for completeness that WWII 4.5" naval came in both fixed and separate forms, depending on the turret. Data from Navweaps, which gives 114x695R for the fixed round, but 114x645R for the separate (I'd presume the difference in dimensions is the overlap between case and shell in the fixed round).
4.5" QF Mk I in Mk I UD Single, Fixed
4.5" QF Mk I in Mk II BD/RP10 Mk II* BD/Mk III UD Twin, Fixed
4.5" QF Mk III in RP10 Mk II** BD, Fixed?
4.5" QF Mk III in Mk II*** BD Twin, Separate
4.5" QF Mk IV in Mk V/RP50 Mk V/RP50 Mk V*/Mark 5* Mod 1/2 Single, Separate
4.5" QF Mk IV in RP10 Mk IV/RP10 Mk IV* Twin, Separate
4.5" QF Mk V in RP 41 Mk VI/VII Twin, Separate
 

monochromelody

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might the 17pdr tank gun have been replaced with a larger calibre version with a more effective shell?
The answer might be yes, I have heard there were plans about fitting a 3.7in barrel with a 17pdr chamber so that it could fire bigger HE shells. Sort of like what they did to mate the 3.7in howitzer barrel with 25pdr breech to make a 95mm CS howitzer.
 

EwenS

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The very high-velocity 3.7 inch Mk VI fired 94 x 857R mm ammunition with a 150mm rim.
The WW2+ 4.5 inch naval/AA guns using fixed ammunition fired 114 x 695R mm ammunition with a 167mm rim.

Definitely not going to argue cartridge dimensions with an expert, but worth noting for completeness that WWII 4.5" naval came in both fixed and separate forms, depending on the turret. Data from Navweaps, which gives 114x695R for the fixed round, but 114x645R for the separate (I'd presume the difference in dimensions is the overlap between case and shell in the fixed round).
4.5" QF Mk I in Mk I UD Single, Fixed
4.5" QF Mk I in Mk II BD/RP10 Mk II* BD/Mk III UD Twin, Fixed
4.5" QF Mk III in RP10 Mk II** BD, Fixed?
4.5" QF Mk III in Mk II*** BD Twin, Separate
4.5" QF Mk IV in Mk V/RP50 Mk V/RP50 Mk V*/Mark 5* Mod 1/2 Single, Separate
4.5" QF Mk IV in RP10 Mk IV/RP10 Mk IV* Twin, Separate
4.5" QF Mk V in RP 41 Mk VI/VII Twin, Separate
The switch from fixed to separate rounds was made in mounts designed from 1942 onwards because the earlier rounds were too heavy to allow rate of fire in larger ships to be maintained, and would only have got worse when fitted in destroyer sized vessels.

The one piece round was 87-92lb. Breaking it in two gave a shell of 55-58lb with a case of 32-34lb. Much easier to handle on a pitching destroyer.
 

Petrus

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might the 17pdr tank gun have been replaced with a larger calibre version with a more effective shell?
The answer might be yes, I have heard there were plans about fitting a 3.7in barrel with a 17pdr chamber so that it could fire bigger HE shells. Sort of like what they did to mate the 3.7in howitzer barrel with 25pdr breech to make a 95mm CS howitzer.

Please note that when the Centurion was being developed, its derivative armed with a 32-pounder (or other similarly powerful gun) would have accompanied the standard Centurion with the 17-pounder.

In "The Centurion Tank" by Bill Munro there are few remarks on that:

A self-propelled artillery version was planned, with a 3.7in 65-calibre anti-tank gun or howitzer or field gun heavier than 95mm or 25-pounder. This should be capable of firing HE, smoke and hollow-charge projectiles.
Provision was also be made, if possible, for a 32-pounder gun for use in an engineers' vehicle.

At https://www.facebook.com/TheFriends...ok-at-the-little-known-vick/2214932102060128/ you may find an article on the project designated Vickers SP.4:

One of the more interesting vehicles to have been unearthed recently is the Vickers SP.4. Its origins lie back in 1943 when the A41 was first envisioned. As was customary when a new tank was being designed various support roles are often planned these typically include bridge layers, recovery types and support or assault vehicles. Centurion initially was to have a mixture of 95mm Close Support (CS) tanks at a 10% ratio to regular gun tanks but this idea quickly vanished while centurions armament was being heavily debated (it would appear later as the Mk IV albeit just the one). Of the weapons planned for Centurion several are listed, the 77 mm, 17 pounder, 21 pounder (which would go on to form the 20 pounder gun), the 32 pounder, and planned 37 and 55 pounder tank guns.

Centurion would go on to be initially produced with the 17 pounder, however the larger 32 pounder gun was not forgotten and although its large size and slow handling made it suitable only for assault roles it was tested out in at least one Centurion tank, albeit with a 14 inch thick rigid mantlet. The 44th and 45th Tank Board minutes held in November 1944 and January 1945 stipulated that for the 32 pounder to enter production along with supporting platforms they needed to have at least 25% greater armour penetration capability and not less than 25% slower reloading and laying.

It was therefore deemed that to get the best performance from the gun it would need to be mounted in a heavy vehicle and fired from a static position ideally in a limited traverse casemated superstructure. This had already been the plan for the A39 Tortoise (the name Tortoise is the class of vehicle not the individual machine’s name), a separate multi wheeled platforms had been devised by Nicholas Straussler and the third option was for a Centurion based Tank destroyer which was simply referred to as SP.4.

The layout consisted of a raised superstructure which extended over the hull sides in a boxy slab sided configuration not too dissimilar from Tortoise. The armour was relatively thin although not directly specified it would appear from the plans to be 2-3 inches at the thickest which would indicates a certain degree of mobility being required. The primary difference was in firepower. While Tortoise maintained a 32 pounder with two loaders, SP.4 would come equipped with either a 21 or 32 pounder gun with a fully automatic loading mechanism with 8 rounds in a large hopper. It’s unknown where the idea from this came from but it has been suggested it may have been tied to a project to mount the same weapon on the mosquito fighter bomber for anti-shipping use although no clear confirmation of that can be sourced.The plans themselves show it fitted with the 20 pounder gun or envisioned one as the muzzle break was never fitted in the style shown.

The crew consisted of three men, the Driver, Commander and Gunner (loading was automatic) the blueprints don't show who is who but they are all situated on the left hand side of the vehicle as the autoloading mechanism takes up the right hand side. The Commander is offset to the right side and sits above the track. Ammunition is stored to the drivers left and in two racks above the cheeks over the tracks. 45 rounds are carried, 27 on the left hand side, 9 on the right and 9 in the nose.

Although full pans were drawn up by Vickers (ref: T44251) no production or even conversion would take place. The Tank board was dissolved at the end of December 1944 and became the A Vehicles Committee and many of the war time oddities were silently put to rest. Tortoise would get as far as 6 prototypes but only used for measuring roads and bridges in the BAOR to gather data for the next generation of heavy tanks, the UK chose to use SP.2 Avenger as an interim Anti-tank vehicle and shortly after Centurion proved itself capable of performing the role itself. Today only a few blueprints and mentions in the minutes are all that’s left of one of the most elusive of the Centurions variants.

Provisional specifications as listed on the blueprints:

Total weight: 24 tons (24.385 kg)
Height: 8 ft 1 inch (2,46 m)
Length with gun: 30 ft 4 inches (9,25 m)
Length without gun: 19 ft 4 inches (5,89 m)
Width: 9 ft 9.5 inches (2,98 m)
Track centers: 7ft 8 inches (2,34 m)
Ground clearance: 18 inches (457 mm)
Gun: 20 pounder or 32 pounder
Gun depression -5 degrees
Gun elevation +20 degrees
Gun traverse 12.5 degrees left and right
Ammunition 45 rounds + 8 ready to use.

Piotr
 

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Nick Sumner

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Was the chassis shortened? The Centurion chassis had 6 wheels per side, the drawing shows 5...
 

Basilisk

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Looks like a whole new vehicle, see the 5 pairs of small circles in the bottom of the hull? That's how torsion bars usually appear in a cross sectional view like that.
 

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You can bet there'll be an Armoured Archives video about it soon, the Facebook article is one of Ed's older ones which are gradually turning into full-blown videos. He may tell us more then. However it was drawn up during the early design of the Centurion, so maybe the drawings are based on an earlier version? It's certainly very different to your average Cent's horstman arrangement. I could try asking him on the channel's discord if you'd like?
 

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And the drawing in full
 

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The version above from Facebook is a copy of the orginal by Ed to sharpen it up. It is indentical in technical aspects. He is just showing us a bit of the original as proof. When I said 'full' I meant full size, sorry about the confusion.
 

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