Up Gunning - why was it so difficult?

[ajmac]

Post war (WW2) many wartime tanks were upgunned, some to a main gun that was already available towards the end of the conflict, others ended up with 'massive' calibre upgrades compared to there original issue. Many vehicle histories state that futher up gunning was impossible due to the limited size of the turret ring... then later on in the history they go to show just the modifications that in wartime were supposadly a non-starter. What is all that about?

 

In question:

Cromwell > Charioteer

Sherman 75mm turret. > M50?? (the one with the 'nose' welded onto the front of the turret)

Sherman 75mm turret > 76mm wartime weapon that was originally in the larger turreted 76mm Sherman

Edited January 20, 2010 by ajmac

[Adrian Barrell]

In wartime it was not always possible to develop new ideas or at least expend the energy indulging what were often seen as being unrealistic ideals. Quite how you equate that attitude with some of the dubious descisions made with regard to British tanks, I wouldn't like to say!

 

Having said all that, until you're in that mans shoes......

 

Cromwell to Charioteer required a larger turret ring and a consequent modification to the roof. Cromwell turret ring is 60" dia, Charioteer 64" and is a much more massive assembly.

 

Sherman used a 69" turret ring and is noticeably more roomy inside than any equivalent British tank.

 

The M50 conversion moved the trunnions forward in that beak like casting which is incidentally bolted onto the turret using the original gun mount holes. The consequent moving forward of the centre of gravity required the large casting welded on to the back of the turret.

 

The 76mm gun was very similar in dimensions to the 75 other than in barrel length.It was not an equivalent of the 17 pr in any respect until the advent of the HVAP ammo. The 75 and 76 share many breech componants and the rings a are of a similar size.

 

Ultimately, it was the size of the turret ring that gave Sherman the edge on it's ability to be upgunned.

[woa2]

On a similar point, I remember that there was a plan to modify the Lancaster in WW2 as an escape hatch was a bit small and needed to be made bigger so that aircrew could bale out easier. The modification was turned down as it would have meant stopping production for a short while during wartime, and this was deemed unacceptable.

Also, was this the same reason that the Jeep didn't get a decent hand-brake until after the war?

[steveo578]

The Charrioteer had a relatively high trunnion height to overcome the limitation of the size of the turret ring which although it was larger than the Cromwell is still comparatively small 64inch as opposed to 60inch but was very heavily made . The high trunnion trick was also used in the A30 Challenger which had a 65inch ring. The primary problem with a small turret ring is the inablity of long rounds being loaded when the gun is at certain elevations- in addition larger rings are often stronger- but not always, for example the Sherman 69inch ring is not as strong as the Charioteer and some say not as strong as a Cromwells 60inch or a Churchills 54inch. The Soviet T62 got around the large ammunition problem by having the gun drop to horizontal during loading in a similar manner to some field or medium guns do.

 

The Other types mentioned. The Israeli M50 mounted at CN N 50 gun which is about the same as a 17pdr, similar KE, slightly longer recoil throw and similar ammunition size. However the extended front of the M50 was actually un-necessary as the Indians had the same weapon in Sherman V using the original mantlet as did the Argentinian 90mm replacement of 17pdr in their M4C, which used the same recoil mechanism. Further the Israeli M51 used more or less the same recoil mechanism and orignial trunnion position for the F1 105mm gun.

 

The small turreted 76mm gun tank M4 , the 76mm gun was designed for the original 75mm gun turret and most components apart from the barrel were similar to the 75mmm gun but with beefed up recoil cylinders, but the Armor Board considered it too cramped -which was an excuse -they did not rate the 76mm gun and were playing games with the ordnance- so the T23 turret was used instead making the VVSS M4 76 somewhat top heavy.

 

Photos Web photo of Indian Army Sherman V with CN N 50 (AMX13 75mmgun)

Two excellent photos from another HMVF thread showing the exterior and interior of a Argentinian Sherman firefly modified with a French/Beligan 90mm gun note the AMX style Slide beneath the breach, similar to that used in the Israeli M50 -51 photos of these will be posted later.(scanner problem)

 

Steve

[steveo578]

Shown are two photos of the interior of the strange A30 turret (one is the TOG 2 prototype not in A33 as in the caption), the A30 turret shows the comparatively high trunnion height allowing loading of the large 17pdr shell. The Tog photo show the bazar roller ring something akin to a Naval barbette. In addition (but not visible in this photo) a large ball bearing approx 4inches in diameter beneath the floor taking much of the recoil loading. In addition the whole turret could be raised a few tenths of an inch around this bearing by a jack to clear debris on the roller ring. In hindsight madness but it has to be remembered we have the benefit of hindsight.

 

Third photo of an interior view of a Pershing a T26E4 trial vehicle loading a T15E2 shell into the breach showing the problem of shell length at certain elevation angles. This gun was in fact a separate loading weapon, the original T15E1 was trialed in the Wartime Super Pershing by 2AD just before the end of the War in Europe. The problem was resolved by using a fatter T54 round which in turn required a larger breach and therefore a concentric recoil system to save space- concentric systems requiring better seals- and so it goes on. Photo from Pershing by Hunnicut- really good book which may still be available having recently been re-printed.

[Adrian Barrell]

Charioteer ring has a greater section size than Sherman and being smaller in diameter is, I would think, stronger. Whoever says Cromwells ring is stronger than Sherman has clearly never seen one. It is fairly weedy in comparison.

[Richard Farrant]

Also, was this the same reason that the Jeep didn't get a decent hand-brake until after the war?

 

 

I know this is off topic, but to answer your question, Robert. The Jeep transmission brakes were changed to internal expanding (ie drum brake) in July 1944.

[steveo578]

M50 and M51 modification

 

The Israeli M50 mantlet is shown in photo1 and the interior view shown in photo 2 note the inner section bolted to the standard mantlet bolt holes as previous mentioned by Adrian. Note the recoil throw indicator on the breach showing a throw between 300-and 350mm was acceptable beyond that a recharging of the recoil system is required.

 

The Israeli M51 mantlet interior in three photos, the the gun is a modified F1 fitted to an AMX30 but the recoil system has more in common with the AMX13 FL12 fitted in Dutch AMX13s, the huge size of the D1504 (f1) breach is apparent note the recoil cylinder ends in the left side photo. In the second photo beneath the breach the recoil cylinders are the large green lump. This mechanism is much softer than comparative systems such as 20pdr/105mm L7A1 which have about 2/3rds the recoil stroke. It is said that when the Israelis trialed a 20pdr in a Sherman that it damaged the turret ring.

[Tony B]

The thing is most people get it the wrong way round. The ammunition is designed first, then a gun to chuck it out of. The need is to defeat the oppositions latest armour. So a Ballastician designs a new shell and propellant, the enginner then has to design a breech to hold the charge in,physical and explosivly, a new rifiling set, a new barrel to stand the weight and speed of the projectile, consider that you are chuking a lump of metal from standstill to 1000g in les than a heart beat. Then produce design drawings, then manufacture one and fire the beast, then sort out all the little problems you hadn't considered. Then re tool then allocate materials, including somewhere a new alloy or process, bet on it. Then start changing the vehicle to fit the whole new contraption. That it happned at all in five years is a miracle!

[ajmac]

Nice discussion guys. Steve, out of interest, it looks like that M50 is in the UK, is it being restored as an M50 or is it being sent back in time :-) I rememeber that last year someone mentioned that an Isreali Sherman was being restored in the UK. Sometime I feel a little sad that post war modifications are generally fround upon and removed in order to get back to 'proper' spec during a restoration, but hey, I know I would do the same!

 

NB: I'm not a sad case, up at 1:50am writting this, it is 8:20am in this neck of the woods!

Edited January 21, 2010 by ajmac

[fesm_ndt]

I heard a story from a gent over here who was involved in the, from memory Thai Scorpion mods. Apparently the recoil wasn't assessed correctly and the wheels were snapping off

[mcspool]

The Israeli M51 mantlet interior in three photos, the the gun is a modified F1 fitted to an AMX30 but the recoil system has more in common with the AMX13 FL12 fitted in Dutch AMX13s, the huge size of the D1504 (f1) breach is apparent note the recoil cylinder ends in the left side photo.

 

Steve,

 

Great input. Apart from the problems you mentioned the French and Dutch found out that upgunning at some point will also affect the turret structure. The Dutch Army requested their AMX-13's to be equipped with the 105mm gun, this variant was designated AMX-13/105 Modèle 58 by the French. Some time after being taken in service, the Dutch Army noticed cracks in the FL-12 turret's casting. At first it was thought this was due to bad casting or metallurgy, but later it turned out the 105mm guns' recoil force was causing the cracks. All sorts of modifications were carried out, the main one was restricting its use!

 

Buying the AMX-13 fleet turned out to be a disaster. Apart from the above, how are you going to fit the largest people in the world in armoured vehicles designed for one of the world's smallest people?!?! Technically they were not very relaible either. Today, even as targets they do not very well as the armour is too thin. . .

Rumour has it that the French were going to sell their Mirage fighter aircraft to the Dutch Air Force, but due to Royal intervention they bought the Lockheed Starfighter instead. Then the Dutch MoD decided to buy AFVs off the French to keep our relations stable.

 

Oh well.

 

- Hanno

[Adrian Barrell]

 

Apart from the above, how are you going to fit the largest people in the world in armoured vehicles designed for one of the world's smallest people?!?!

Oh well.

 

- Hanno

 

:rofl:

[steveo578]

ajmac

it looks like that M50 is in the UK, is it being restored as an M50 or is it being sent back in time

 

 

The M50 I photographed was and probably still is at Eden Camp in Yorkshire, a former POW camp mainly for Italians now a theme park disneyesque history experience. I would imagine it is now painted with white stars and Olive drab, but I doubt anything has been done in the inside since it arrived on the ship on the humber when Budge brought it in (numbered DB5 by budge), it still had lots of junk inside such as 7.62 cal MG belt links and track links thrown into the turret.

[mcspool]

:rofl:

Funny isn't it?!?! And then the big guys asked the small guys to fit a bigger gun in their small tank - or should I say "tankette"? A typical case of trying to get the biggest bang for the guilder. . .

 

In the early 1960s the AMX-13 replaced the M24 Chaffee in Cavalry Recce units. I can see why Recce units want a small tank, but why did they need an upgunned one?

 

H.

Edited January 21, 2010 by mcspool

[steveo578]

Apart from the problems you mentioned the French and Dutch found out that upgunning at some point will also affect the turret structure.....

 

Thanks for that input, I wasn't aware of the problems with the AMX13/Fl12 but I'm not surprised it's far to big a gun on a small chassis even the 75mm Fl10 is probably too much, I think the designer believed the mass of the upper portion of the oscilating turret bearing on the lower section would make up for lack of structure, having said that a relatively small-"air portable" recce cum tank destroyer was really asking too much from the design, T.D.s in particular need to be robust to fire consistantly whereas a recce vehicle to be successful should fire rarely.

 

The AMX13 is very small if you're more than 170cm tall its almost impossible to close up, far better to design a tank around 90% stature male as the U.S. do. I would still quite like an AMX13 or an EBR- the early post war french tanks have an appeal but not if you've got to use one for real.

 

Strange you should mention the F104 Starfighter as last night I was sorting my old photos and came across photos of the RNAF F104 that crashed on Otterburn Training Area in 1983, if I remember correctly (but aircraft aren't really my thing) some at least were built or assembled by Fokker, which is often a deal clincher for Governments.

 

regards

 

Steve

[steveo578]

As a Post script to Post#5 I found the photo of the A30 ball mechanism when it was at Bovington. In addition note the small rotating rack and large traversing motor to the left.

 

a30 ball.jpg

[Stone]

You could just go for the Russian approach and forbid any crew from being over 5'4"! :cool2:

 

Not sure which tank that started on but making the short crewman assumption allowed them to shave a couple of inches off the silhouette...

 

Stone

[steveo578]

Stone

Not sure which tank that started on but making the short crewman assumption allowed them to shave a couple of inches off the silhouette...

 

 

A20 T34/76, before that most soviet Armour was based on foreign designs T26 based on Vickers 6tonner. BT the US T3 Christie, T18 in effect an advanced Renault FT 18. Indiginous designs such as T28- T35 seem to have been designed to impress (Kinder Shreck) so size wasn't an issue.

[mcspool]

You could just go for the Russian approach and forbid any crew from being over 5'4"! :cool2:

 

 

That is what they had to do in the end: select the smallest guys from the draftees.

 

Could work for tank crews, but not for APCs as you would have to restrict entire infantry battalions in height. . . So it was get in, move over and shut up.

 

H.

[mcspool]

Thanks for that input, I wasn't aware of the problems with the AMX13/Fl12 but I'm not surprised it's far to big a gun on a small chassis even the 75mm Fl10 is probably too much, I think the designer believed the mass of the upper portion of the oscilating turret bearing on the lower section would make up for lack of structure, having said that a relatively small-"air portable" recce cum tank destroyer was really asking too much from the design, T.D.s in particular need to be robust to fire consistantly whereas a recce vehicle to be successful should fire rarely.

Yes, after being used by Recce units, the Dutch AMX-13's were used in an anti-tank role, first with artillery and then infantry units. They were not a succes in that role either. . .

 

- H.

Edited January 21, 2010 by mcspool

[mcspool]

Strange you should mention the F104 Starfighter as last night I was sorting my old photos and came across photos of the RNAF F104 that crashed on Otterburn Training Area in 1983, if I remember correctly (but aircraft aren't really my thing) some at least were built or assembled by Fokker, which is often a deal clincher for Governments.

Yes, Fokker built large numbers of F104's during 1962-1965 under licence. Later also F16's, but it won't happen with the F-35 as the aircraft assembly part of the company no longer exists, only components and services.

 

That F104 at Otterburn was one of many to fall from the sky. . .

 

H.

[steveo578]

Mcspool

Could work for tank crews, but not for APCs as you would have to restrict entire infantry battalions in height...

 

 

Probably less of a problem when the Soviet Union was in existance, small asiatic troops could fit both tanks and APCs but post comunism things will have become a little tight. BTR 60-70 and 80 were difficult to access through the little door between wheel station 2 and 3 and sighting the 14.5mm turret MG is not so easy if your tall. The Czechs and the Poles prefered the OT64, but I was recently told that the Ukranian paras who were "big lads" used the BTR 70 or 80 for peacekeeping in the Balkans.

 

There is an overfire problem with the BMP1 the zero elevation fire height of the weapons is about 170cm.

[AlienFTM]

That is what they had to do in the end: select the smallest guys from the draftees.

 

Could work for tank crews, but not for APCs as you would have to restrict entire infantry battalions in height. . . So it was get in, move over and shut up.

 

H.

 

As described to us back in the day. Selection for Russian conscripts:

 

Tallest on the left, shortest on the right, in single rank SIZE.

 

From the right NUMBER

 

1 2 3 4 5 6 7 8 9 10 ... 100,000 last man SIR!

 

(So now you have a single line of 100,000 conscripts with the dwarves in the low numbers and the giants in the thousands.)

 

Numbers 1 - 50,000, you are assigned to the infantry. Remainder stand fast. To your duties FALL OUT.

 

Numbers 50,001 - 75,000, you are assigned to armour. Ditto.

 

And so on. At the end of all this, the right people were selected who could fit into a BMP, then those who would fit into a T62. Choice? You wanted choice? Why do you think it's called conscription?

 

So yes, we were told that Russian (and presumably Soviet since they shared the technology) infantry battalions were selected by size.

[steveo578]

Does anyone have a Comet TM or any documentation regarding the recoil throw of the 77mm gun fitted to the A34. I was reading Universal Tank and wondered about the problems with the Vickers 75mm HV design, at one stage it was to be fitted to both Cromwell and the A42 (heavy) Churchill MK7.

 

Steve