British "75mm AT gun"...

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Clive Mortimore
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Re: British "75mm AT gun"...

Post by Clive Mortimore » 22 Jul 2012 19:43

phylo_roadking wrote:
Very true but that was the whole gun and recoil system not a cut down gun and a new mounting and recoil system.
Paul and I discussed this both on and off the board at the time. It "looks" (there are pics) like the MkI (or I*) 3" 20cwt and recoil system was mounted on a redesigned but quite simple pedestal mount inside the Gun Carrier's "armour box"...with a little round mantlet mounted on the gun so that it just overlapped the edges of the hole in the box's armoured front face! :P Not a lot of time (equals money, after all!) seems to have been spent designing the new mount... :P
Hi Phylo

Are you talking about the photos of the gun carrier pulled off the ranges recently, where you can see inside the fighting compartment? They do show the same recoil system as on the AA gun. I also recall seeing some pages of the manual showing the interior stowage which show the same mounting.
Paul_G_Baker wrote:
At least Pemberton seems to think they were a bit more substantial than "Nessie"! :wink: :wink:

Probably they were all re-barreled with the correct weapon as soon as production caught up - and there's always the chance that those intended for the ME were sunk en-route....
Hi Paul

Pemberton does not give any more information than Hogg, it is possible that is where Hogg got his information from. For the guns to have been accepted in service there would have had to be some form of handbook, they done one for the 50 SP guns. There would have had to be something like a range table. New sights those from the AA gun would not have fitted the 17 pdr carriage. A anti-tank gun is no good without sights. 50 gun tractors with a different stowage arrangement would have not gone past the vehicle enthusiasts noses without comment.

What does seem strange that in the Pemberton report the carriages were well in advance of the guns in April 1941? The 17 pdr was not approved of until May 1942 and to get it into action as soon as possible where the guns that were advance of the carriage production the guns were mounted on 25 pdr carriages. So the carriage building programme must have been slowed down from April 1941, before the approval and September 1942 when the first 17/25 pdr was test fired.

It still beats me that 50 guns were made and no official photo or an unofficial one. How many twin 6 pdr anti aircraft guns were made? How many photos of the two of them? The British liked to photograph their development weapons, photos the 17pdr Straussler Monitor is well published and so is the Thornycroft Amazon 17 pdr SP. So why not the 3 inch gun on the 17 pdr carriage after all neither parts the gun or the carriage were top secret.

Which units did they go to, or did they remain in storage like the 95mm Infantry Howitzer?

As for them being re-barrelled with a 17 pdr gun I am sure that would have been documented. If they would have been lost at sea they would appear on the Lloyds register as cargo losses.

Yours

Clive
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Re: British "75mm AT gun"...

Post by phylo_roadking » 22 Jul 2012 19:58

Are you talking about the photos of the gun carrier pulled off the ranges recently, where you can see inside the fighting compartment? They do show the same recoil system as on the AA gun. I also recall seeing some pages of the manual showing the interior stowage which show the same mounting.
Yes, the gun and recoil system is complete and stock...but the pedestal mount they're in in that application seems to be unique to the Gun Carrier as far as I can tell.
New sights those from the AA gun would not have fitted the 17 pdr carriage. A anti-tank gun is no good without sights
Be interesting to see...if we ever find out...if they were the same as those for the Gun Carrier, or adapted from - and which came first...
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Re: British "75mm AT gun"...

Post by Clive Mortimore » 22 Jul 2012 23:38

Hi Phlyo

I have found the handbook drawings and they do show a sight that is not the same as the ones fitted to the AA gun.
http://forum.axishistory.com/viewtopic. ... r#p1693660
The sight for the gun on the 17 pdr carriage would have to be able to fit the 17 pdr sight mounting. Simple enough to do just use a 17 pdr sight body with new lenses and graticules to match the 3 inch gun ballistics. But each sight design had its own nomenclature, as do its boxes etc. all relating to the gun they are supposed to fit. How does the QM know what to send to a unit if the gun does not appear on his list.

There are so many unanswered questions. Where they Mk1 guns with sliding block breaches or Mk3 guns screw breaches? Did they require a muzzle brake?

I still remain unsure about these guns. I do have a feeling that there has been some confusion in the official channels and it is the 17 pdr guns on 25 pdr carriages that went to the Middle East which has been misinterpreted as these 3 inch anti-tank guns. I do feel that 50 guns were put aside for conversion but I am not convinced they happened. What backs up my idea is the lack of official documentation when the 50 guns put aside for conversion to Churchill gun carriers have the full gambit. So why one half of the project but the other half not?


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Re: British "75mm AT gun"...

Post by phylo_roadking » 23 Jul 2012 00:02

Clive, in the meantime I've come across THIS

http://nigelef.tripod.com/anti-tank.htm
3-inch 16-cwt, in 1941 100 outdated 3-inch 20-cwt AA guns were converted to anti-tank guns. These AA guns already had 12½ lb AP shot and telescopes. 50 ordnance were mounted on Churchill tanks and 50 on new 17-pdr carriages, the latter were issued equally to Home and Middle East Forces, the former had very limited traverse (7 degrees) and were only issued to Home Forces.
...wish I knew what he was using for sources!

At the bottom of the page, however - I can't helpt thinking that THIS might shed some light on the issue of what occured in the Middle East...
Middle East Training Publication (METP)

METP No 12, Part 4 Notes on Anti-tank Shooting - Field Equipment (undated) replaced by Part 4A, June 1942
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Re: British "75mm AT gun"...

Post by Clive Mortimore » 23 Jul 2012 13:51

phylo_roadking wrote:Clive, in the meantime I've come across THIS

http://nigelef.tripod.com/anti-tank.htm
3-inch 16-cwt, in 1941 100 outdated 3-inch 20-cwt AA guns were converted to anti-tank guns. These AA guns already had 12½ lb AP shot and telescopes. 50 ordnance were mounted on Churchill tanks and 50 on new 17-pdr carriages, the latter were issued equally to Home and Middle East Forces, the former had very limited traverse (7 degrees) and were only issued to Home Forces.
...wish I knew what he was using for sources!
Brig Pemberton's book is listed as one of his sources. Most 3 inch 20cwt AA guns should have had two telescopes. One for the elevation layer and one for the traverse layer, in an emergency they could be used for anti tank work but with the 17 pdr carriage a single sight was rtequired which would have meant replacing the lenses for Anti-tank shooting.
At the bottom of the page, however - I can't helpt thinking that THIS might shed some light on the issue of what occured in the Middle East...
Middle East Training Publication (METP)

METP No 12, Part 4 Notes on Anti-tank Shooting - Field Equipment (undated) replaced by Part 4A, June 1942
This change could well be in the change of tactics after reveiwing the anti -guns in battle.
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Re: British "75mm AT gun"...

Post by YAN » 23 Jul 2012 14:23

I see that the Dutch KNLI received 50 of these weapons, what was the Dutch name for these guns?

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Re: British "75mm AT gun"...

Post by phylo_roadking » 23 Jul 2012 14:58

Brig Pemberton's book is listed as one of his sources. Most 3 inch 20cwt AA guns should have had two telescopes. One for the elevation layer and one for the traverse layer...
Except...maybe not? Certainly in the Gun Carrier, and IIRC there was something mentioned in connection with the as-yet uncorroborated A/T guns - they had very limited traverse, a maximum of 7 degrees. Surely that would obviate the need for a full-traverse "telescope" as such if completely re-carriaged?
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Re: British "75mm AT gun"...

Post by Paul_G_Baker » 23 Jul 2012 15:38

phylo_roadking wrote:
Brig Pemberton's book is listed as one of his sources. Most 3 inch 20cwt AA guns should have had two telescopes. One for the elevation layer and one for the traverse layer...
Except...maybe not? Certainly in the Gun Carrier, and IIRC there was something mentioned in connection with the as-yet uncorroborated A/T guns - they had very limited traverse, a maximum of 7 degrees. Surely that would obviate the need for a full-traverse "telescope" as such if completely re-carriaged?
Wasn't the sight actually part of the 17pdr carriage? Ditto the laying handwheel positions?
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Re: British "75mm AT gun"...

Post by phylo_roadking » 23 Jul 2012 16:28

Yes, Paul - but my point is that a separate traverse telescope wasn't necessary on either IIRC? :wink:
A most important component of an anti-tank gun is its sight, a 'sighting telescope' in British terminology. With the exception of the 25-pdr which also had a telescope, field and medium guns would engage tanks using their normal dial sight. In poor light or when the target couldn't be seen through an optical sight then an open sight (basically the same sort of thing as a rifle sight) was used. Range was set using a range drum that was part of the sight mount. This range drum 'clicked' when changed so that the layer could change the range by feel without removing his eye from the telescope. The graduations on this range drum determined the maximum possible anti-tank range, longer range indirect fire was possible but required a field clinometer to lay in elevation according to the data in the Range Tables.

6-pdr - initially had a 900 yard range drum, subsequently modified to 1200 yards.
17-pdr - from early 1944 3000 yard range drum, 1 click 100 yards to 1500 yards, 50 yards over 1500 yards.
The normal pattern for anti-tank telescopes was 'cross-hairs' their full height and width and vertical graticules aligned in a horizontal row that measured an angle (usually graduated at 30 second intervals). These marks were on a movable diaphragm in the sight that could be adjusted as part of the sight testing and zeroing procedures. Early model telescopes such as the No 24 used with 2-pr and No 22C used with 6-pdr and 25-pdr had a ×1 magnification and 21 degree field of view. The No 41 used with 17-pdr initially had the same magnification and field of view.
...the field of view in the existing sight accomodated the limited traverse available ;) The putative 3" A/T conversion's seven degrees of course was FAR less than the 17pdr's thirty degress...and could possibly have been accomdated within the horizontal field of view available in the 20cwt's existing elevation telescope?

Do we happen to have a "No." or "Mark" available for the sights fitted to the Gun Carrier? Or do we know it was the same sights as the Churchill gun tank?
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Re: British "75mm AT gun"...

Post by Paul_G_Baker » 23 Jul 2012 17:09

Phylo,

What's the betting that the "telescopes" in that text refer to the item fitted to the Gun Carrier (and provided on the basis that the original plan was for 100 Gun Carriers!)? Remember that the sighting position was not only higher than, and offset from, the axis of the bore/trunnions but it was also on the wrong side!

I don't think that the putative 17pdr conversion would have required anything but the 17pdr's built-in sighting telescope. As to the traverse, probably less than the full 30°, but (due to the traversing mechanism also being part of the carriage) probably somewhat more than a paltry 10°! :wink:

On the diagrams there is a notation of "Case Spare Tel No.6 for No.30 Tel" if that means anything to you - it's ajacent to "Bottle, Compound, Anti-Dim, No.2", but also just above "Satchel Signals"! :?
http://forum.axishistory.com/viewtopic. ... &start=735
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Re: British "75mm AT gun"...

Post by phylo_roadking » 23 Jul 2012 18:12

Ah! Well, that DOES clarify it - IIRC the "No.30" is the immediate predecessor to the "No.33 sight" as fitted to the Valentine (2pdr), Matilda Mk2, early Churchills, Tetrarch, Covenanter, Crusader and several armoured cars; the No.33 was just a minor simplification of the No.30.
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Re: British "75mm AT gun"...

Post by Clive Mortimore » 29 Jul 2012 01:35

Using my gun fitter background I have been considering the engineering aspects of mounting the 3 inch 20 cwt barrel on the 17 pdr carriage.

If the barrel was mounted on the 17 pdr cradle it would need a jacket for the supporting slide to rest on the cradle, not to hard an engineering job to do. The more serious engineering task would be how to connect the barrel to the recoil system. This is normally done by bolting on to the breach ring. The 3 inch gun and the 17 pdrs hand different designs of recoil systems and to fit the 3 inch to the recoil system would either mean a new breach ring (and block as they were matched pair) or an adapter that connects the two together. The latter would be easier to make. See the drawing the areas I am mentioning are circled red. So for this mating two major components would need to be designed, ordered and made, all this for 50 guns without any official authorisation?

The other method is to use the recoil system from the 3 inch gun, providing the saddle of the 17 pdr is wide enough to accept the cradle from the 3 inch gun. Looking at photos of both guns there would have to be some work on the trunions as they appear to be different diameter. If it 3 inch cradle fits between the saddle then a new elevating arch will have to be made to match the 17 pdr elevating gear. Or new elevating gear would have to be made to match the elevating arch from the 3 inch gun. Circled in red on the drawing. A new saddle would leave very little of 17 pdr carriage left. Again the question is a lot of work without any official authorisation.
3 inch a-tk gun.png
I still remain confused that an expensive new carriage was mated with an old design of gun. Yet to get the new gun into action fast it was mounted on a field carriage not those new “surplus” ones with the old barrels on them.
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Re: British "75mm AT gun"...

Post by Paul_G_Baker » 29 Jul 2012 07:24

Clive,

Did you ever run across a 25pdr carriage holding a 17pdr barrel - or hear how that conversion was done? At least that one has been photographed - so we have evidence that it existed!

Regards,
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Re: British "75mm AT gun"...

Post by Clive Mortimore » 29 Jul 2012 09:08

Hi Paul

The cradle on thge 25 pdr and the one on the 17pdr are of very similar design so connecting the breach to the recoil system would have been far easier than that of mating the 3 inch to a 17 pdr cradle.

As for coming across a 17 pdr MkI gun on carraige 25pdr MkII, I am old but not that old :) :)

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Re: British "75mm AT gun"...

Post by Knouterer » 28 Aug 2012 15:11

Paul_G_Baker wrote:
Clive Mortimore wrote: ... 100 old 3-in 20-cwt AA guns were collected, provided with a special 12 1/2 lb shot, and mounted half in Churchill tanks and half on 17-pr carriages, the production of which was in advance of that of the guns. ...
That surprises me. I thought that initially the production of the guns was in advance of that of the carriages, and that for that reason a number of 17 pdr barrels were mounted on 25-pdr carriages in North Africa?
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