British 6pdr/57mm automatic AA guns

[Petrus]

Looking for information on the twin 6 pdr coastal defence (also a warship's weapon) gun (http://www.navweaps.com/Weapons/WNBR_6pounder_10cwt_m1.htm) I found elsewhere on the Internet a cut-out from Ian V. Hogg's books "Anti-Aircraft Artillery" (attached below). The author mentions there that the British worked on anti-aircraft guns in the 57mm calibre, but in the scan there is no detail on the weapons.

Does anybody have further information on the weapons in question? Any input would be appreciated, esp. pictorial reference.

Best regards,
Piotr

 

[Abraham Gubler]

Hogg's "Allied Artillery of WW2" has a lot of info about the 6 lb coastal defence guns and its various adaptions.

 

[Petrus]

In the meantime I've found some pictures of the Twin 6pdr AA gun:

Piotr

 

[CostasTT]

One more of the system in traveling mode.

 

[Tony Williams]

Hogg's "Allied Artillery of WW2" has a lot of info about the 6 lb coastal defence guns and its various adaptions.

Just to clarify; the 1930s 6pdr 10 cwt coast defence gun (commonly known as the Twin Six) had nothing in common with the late-WW2 6pr 6 cwt AA gun, except for the calibre. They fired different ammunition and were different designs, the 10 cwt being manually loaded, the 6 cwt automatic.

Initially the Twin Six mounting had a low maximum elevation because it was designed for engaging small craft at short range (as it famously did at Valetta Harbour, Malta during WW2 - its moment of glory). Later, the maximum elevation was increased considerably to allow it to be used to engage aircraft.

 

[Rickshaw]

Hogg's "Allied Artillery of WW2" has a lot of info about the 6 lb coastal defence guns and its various adaptions.

Just to clarify; the 1930s 6pdr 10 cwt coast defence gun (commonly known as the Twin Six) had nothing in common with the late-WW2 6pr 6 cwt AA gun, except for the calibre. They fired different ammunition and were different designs, the 10 cwt being manually loaded, the 6 cwt automatic.

Initially the Twin Six mounting had a low maximum elevation because it was designed for engaging small craft at short range (as it famously did at Valetta Harbour, Malta during WW2 - its moment of glory). Later, the maximum elevation was increased considerably to allow it to be used to engage aircraft.

Was a new mounting issued or was the existing one modified? What was the nomenclature of the change to the mounting?

 

[Tony Williams]

Campbell's book on WW2 naval weapons lists the Twin Six mountings transferred to the navy for installing on ships as modified Mk 1, with the maximum elevation as 80 degrees. Which implies that the increase in elevation had been a modification.

The mountings in the Malta action had a low elevation, as they were unable to elevate far enough to reach the more distant boats.

 

[DWG]

Just to clarify; the 1930s 6pdr 10 cwt coast defence gun (commonly known as the Twin Six) had nothing in common with the late-WW2 6pr 6 cwt AA gun, except for the calibre. They fired different ammunition and were different designs, the 10 cwt being manually loaded, the 6 cwt automatic.

I've seen at least one reference to a late model hybrid with 6pdr 6 cwt barrels on a Twin Six mounting, that's on the other computer right now, so I'll update with mark numbers later if I remember.

 

[Tony Williams]

I've seen at least one reference to a late model hybrid with 6pdr 6 cwt barrels on a Twin Six mounting, that's on the other computer right now, so I'll update with mark numbers later if I remember.

I presume that was experimental. If it used the 6cwt barrels that implies that it used the 6cwt ammo, which was different from the 10cwt and not interchangeable. I am pretty certain that the 6cwt ammo never entered production, being built only in test batches for the development of the 6cwt gun. Data follows:

10cwt ammo: case length 464mm, rim diameter 79mm, shell weight 2.82 kg, muzzle velocity 719 m/s

6cwt ammo: case length 514mm, rim diameter 89.5mm, shell weight 2.71 kg, muzzle velocity 945 m/s

The 6cwt ammo will have developed noticeable extra recoil, so the 10cwt mounting would have needed to be beefed-up, with a bigger hydraulic recoil management system, to cope.

 

[Rickshaw]

I've seen at least one reference to a late model hybrid with 6pdr 6 cwt barrels on a Twin Six mounting, that's on the other computer right now, so I'll update with mark numbers later if I remember.

I presume that was experimental. If it used the 6cwt barrels that implies that it used the 6cwt ammo, which was different from the 10cwt and not interchangeable. I am pretty certain that the 6cwt ammo never entered production, being built only in test batches for the development of the 6cwt gun. Data follows:

10cwt ammo: case length 464mm, rim diameter 79mm, shell weight 2.82 kg, muzzle velocity 719 m/s

6cwt ammo: case length 514mm, rim diameter 89.5mm, shell weight 2.71 kg, muzzle velocity 945 m/s

The 6cwt ammo will have developed noticeable extra recoil, so the 10cwt mounting would have needed to be beefed-up, with a bigger hydraulic recoil management system, to cope.

I assume the weight in hundredweights is that of the gun and mounting? Surely the gun and mounting weighing 10 cwt would be better able to absorb the recoil of the 6 cwt ammo adequately? It weighs some 4 cwt heavier, afterall.

 

[Tony Williams]

The cwt weight is the gun and breech mechanism, not the mounting.

The recoil problem is actually worse with the lighter barrels, as weight helps in managing recoil (more inertia means that the gun recoils more slowly). Try shooting a magnum loading of any cartridge in a heavyweight gun and then a lightweight one and you will feel the difference....

 

[Rickshaw]

The cwt weight is the gun and breech mechanism, not the mounting.

The recoil problem is actually worse with the lighter barrels, as weight helps in managing recoil (more inertia means that the gun recoils more slowly). Try shooting a magnum loading of any cartridge in a heavyweight gun and then a lightweight one and you will feel the difference....

Yes, that was what I asking about. Thank you.

 

[DWG]

A month later than planned, but I've found the reference to the hybrid mounting. It's in a single page scan of the Twin Six entry from a book (not identified, a footer says "British Coast Artillery", but that might be the chapter) that I found on the web several years ago. I've got a feeling I also found separately a several page PDF on the Twin Six that corroborated it (or possibly repeated it), but I can't find that at the moment.
After discussing the history of the Twin Six (nothing new really) the scan states (with my notes in brackets):
"Ordnance:
Mk 1 Basic Model, Loose Liner
Mk 1/1. Post war modification, breech ring mortise radiussed to prevent cracking during sustained fire.
Mk 2 Monobloc
Mk 2/1 (Modified as 1/1)
Mounting:
Mk 1 : Basic model
Mk 1*: Mk 1 converted to approximate Mk 3
Mk 2 : Mk 4 (sic) altered to become semi-mobile (I suspect this should be 'Mk 1 altered').
Mk 3 : As Mk 1*, but new manufacture (this is a circular definition, but given the Westwood's link below mentions producing conversion sets, I'd suspect Mk 1* and Mk 3 may be the AA capable mountings).
Mk 4 : As Mk 1, but fitted with 6 pdr 6 cwt guns. At the end of the war there was a development programme for a 6 pdr 10 cwt equipment that could elevate to 80 degrees and thus function as a dual purpose coast/AA gun. During the war there was a continuing development of a 6 pdr 6 cwt AA gun which gradually became a dual purpose AA/coast gun. As might be expected, the two became inextricably mixed, which is why a 6 pdr 10 cwt mounting has 6 pdr 6 cwt guns on it."
There's also a page on the Twin Six mounting here http://www.westwoodworks.net/HowItWas/WestwoodWorksInWW2/index.htm#6pounder , which suggests that both 6 pdr 10 cwt and 6 pdr 6 cwt mountings may have been produced by the same supplier, and there's a brief section on the 6 pdr 6 cwt which has some of the few pictures I've seen of the 6 pdr 6 cwt.
I'd presume the 6 pdr 6 cwt installation on the 6 pdr 10 cwt Mounting Mk 4 was a semi-automatic one, given all the reported difficulty with the feed mechanism for the automatic.

 

[Tony Williams]

Very interesting: thanks for the info and the link.

It does raise a question concerning "why a 6 pdr 10 cwt mounting has 6 pdr 6 cwt guns on it".

I can only assume that this was a one-off experiment as part of the development programme. As I've said, the 6cwt used different ammo from the 10cwt, and I've never seen any indication that the 6cwt ammo ever went into production. It is exceptionally rare among ammunition collections - I've never seen one, and never even seen a photo of a complete round.

 

[CostasTT]

Maybe this is also of interest: Twin 6-pdr guns on mobile mounting (screenshot from video). It may well be one of the mounts DWG mentioned.

 

[DWG]

Costas: Yes, that's the one. I found a better picture of it while poking around the web the other night, but didn't think to link to it and can't seem to find it again.
Tony: Agree with you almost completely, but given the extended development of the 6 pdr 6 cwt, and the Westwoods article referring to at least a dozen different prototypes, there has to have been a reasonably number of rounds floating around for proofing the feed mechanisms (the ongoing problem as I understand it), if nothing else.

 

[CostasTT]

Costas: Yes, that's the one. I found a better picture of it while poking around the web the other night, but didn't think to link to it and can't seem to find it again.

Thanks for confirming.
P.S.: Did you try searching your browser history for the photo you mentioned?

 

[DWG]

A month later than planned, but I've found the reference to the hybrid mounting. It's in a single page scan of the Twin Six entry from a book (not identified, a footer says "British Coast Artillery", but that might be the chapter)

Belated follow-up, I found where that reference came from (not that I was actually looking for it at the time, but it rang an immediate bell): British & US Artillery by Ian V Hogg, the scan is in a thread here: http://www.phpbbplanet.com/warshipprojects/viewtopic.php?t=3618&mforum=warshipprojects

 

[Tony Williams]

I have recently added a 6pr 6cwt round to my collection, along with a 42mm Red Queen (see the pic from the Ammo Photo Gallery on my website).

What is intriguing is that the date on the 6pr's headstamp is 1960. Apparently it isn't the only one in existence which was made then. Why were they still making the ammo a dozen or more years after the project was cancelled? No-one seems to know.

From left to right: 40x364R (Bofors L/70 land+naval), 42x270 (British Red Queen exp. AA), 45x386SR (Soviet naval), 57x347SR (Soviet S60 land+naval), 57x438R (Bofors naval - formerly land also), 57x515R (British 6pr 6cwt exp. AA)

 

[Rickshaw]

What is the providence of the round? Perhaps it's a fake, made with a 6 Pdr case?

 

[Tony Williams]

What is the providence of the round? Perhaps it's a fake, made with a 6 Pdr case?

It can't have been made from any other 6pr round because it's longer than any of them.

The method of construction, style of headstamping, screw-in primer hole and so on, are all authentic. For someone to manufacture these rounds (several of them are known) from scratch would require heavy ammunition-making machinery and the cost of doing so would vastly exceed their value to the very small number of collectors willing to buy such items.

These rounds are well-known to collectors and professional dealers in collectable ammunition of this size. There are no doubts about their authenticity.

 

[Abraham Gubler]

Perhaps there was a British commercial 57mm project for export as a rival to the Bofors 57mm? Or there was a British gun project as a back up to Sea Cat that hasn't yet seen the light of day? Pure conjecture but a brace of reasonable reasons as to why someone was making long cased 57mm in 1960.

 

[Tony Williams]

Judging by the very poor performance of the 6pr 6cwt prototype guns, an entirely new design would have been needed to get anywhere near the Bofors. And since the market for such guns in the West was small, and the efficient Bofors had that market sewn up, I can't see anyone bothering to do that.

The last time the British designed, developed and put into service an automatic AA cannon was the 2pr introduced in 1915.

 

[JFC Fuller]

Assuming the head-stamp is accurate the only theory which jumps to mind is that whilst the overall project was cancelled it is possible that low-level research was continued. This was not uncommon at the time, major R&D/procurement programmes would be cancelled but small scale research would continue for years afterwards on specific components and technologies.

 

[Tony Williams]

That's quite possible.

For instance, while the 7mm EM-2 rifle was cancelled in 1951, a batch of the unique ammo for it was made in 1970 (I have one). This was probably in conjunction with the development of the necked-down 6.25mm round which was made for testing in an EM-2 rifle.

 

[CJGibson]

DACR?

Chris

 

[Tony Williams]

DACR is supposed to have been a fast-firing CIWS and I've only seen calibres of 34-40mm mentioned in conjunction with it (although I can well imagine that if 42mm Red Queen had succeeded, it might have been adopted by the RN as well as the army).

Besides, by 1960 the RN seems to have become fixated on SAMs, with Sea Cat being the Bofors replacement.

 

[CJGibson]

I think that, having seen Sea Slug and its boosters making pretty spirals in the sky for such a long time, the Third Sea Lord might have considered an insurance against Sea Cat failure. I'm sure Vickers would have applied Ratefixer work to a 57mm naval AA system.

Chris

 

[smurf]

DACR (Chris Gibson has e-mailed me about this thread.
There are sets of Vickers drawings of two different 57mm versions of DACR in the Cumbrian archives for Vickers guns at Barrow-in-Furness (not the Vickers photo museum)
Chris kindly drew two reduced and simplified profiles for me for my book 'British Cruiser Designs'
The big drawings were unfortunately undated, and there was no technical data.
My computer has gone down (this from my wife's) so at the moment I can't get at any pictures.
If Chris has his drawings still, he is welcome to post them.
Reproducing the actual Vickers drawings involves a ferocious copyright fee, but it might be possible to estimate the length of the case.
PS They were one-man automatic twin turrets.

DACR was quoted for use on the RN "1960 Future Cruiser" designs, and some others dated in the early 1950s, calibre not specified.
The French cruiser Colbert 1959 had 57mm AA and memory tells me there were some NATO commonality studies around then (but my memory is a bit tricksy these days)

 

[Tony Williams]

Thanks Smurf, I'd never heard about the 57mm DACR. That does provide a possible explanation for the existence of the 6pr 6cwt ammo from that period.

The French Navy were early adopters of the 57mm Bofors, using them in their own-design twin mounting in various postwar ships. The ammunition for the Bofors is of course not compatible with that for the 6pr 6cwt.

 

[CJGibson]

OK, now Smurf's let the cat out of the bag, here is a much simplified drawing of the Scheme 1. Scheme 2 had the control cab moved to the bottom right corner. The originals are very cluttered and take a great deal of examination to work out what is going on and what is moving where.

Chris

 

[Tony Williams]

Thank you!

No indication of what type of 57mm gun this was planned for, I suppose?

 

[Abraham Gubler]

OK, now Smurf's let the cat out of the bag, here is a much simplified drawing of the Scheme 1. Scheme 2 had the control cab moved to the bottom right corner. The originals are very cluttered and take a great deal of examination to work out what is going on and what is moving where.

Chris

That is very cool. Like a mini 4.5" Mk 6 turret. Any chance of a scale?

As to the workings it looks like the same kind of feed to the ordnance as on those guns with side mounted rotating pan magazines (Red Queen, etc) except with a linkless belt style magazine (~70 rounds per gun). The magazine probably has a pivot where it conects to the tail part so when elevating this can always be sticking out the rear for access for manual replenishment. Which unlike the Bofors Mk 2 57mm gun would allow for continuous firing without the need for stoping the gun to reload the hoppers.

 

[PMN1]

So what date are the Vickers schemes from?

 

[Abraham Gubler]

Friedman's "Navy Anti-Aircraft Guns and Gunnery" (2013) mentions that Bofors offered both the 40mm L70 and the 57mm L60 to the Royal Navy in the mid 1950s for their new DA gun. After assessment the RN selected the 40mm L70. So this mounting could very much be a British solution for mounting the Bofors 57mm. Which in its Swedish original was considered too heavy by the French leading to their development of their own version. A fascinating "What If?" to consider if the RN had selected the 57mm in place of the 40mm L70 and we saw these guns and mounts on all the 1950s RN ships in place of their Bofors. If they were still onboard by 1982 would have made a big difference in San Carlos.

 

[Tony Williams]

It's a nice thought but I think that a twin 57mm mounting would have been so much heavier that using it instead of 40mm would have been problematic. I suspect it would have required a centreline mounting on any frigate, which begs the question where it would go.

On checking Friedman, the Bofors twin 57mm weighed 30 tons, the French one 16 tons. The RN Bofors Mk 5 water-cooled twin 40mm weighed 6.4 tons, the single air-cooled 40mm around 1.5 tons.

 

[JFC Fuller]

I suspect such a twin 57mm would only be a viable replacement for the sextuple bofors mountings (Mk.6). I have never seen a weight for these but the octuple pom-pom mountings they were meant to replace came in at approximately 16 tons, so right in line with the french twin 57mm.

To my knowledge (happy to be corrected) the RN only took single bofors to the Falklands, all the twin mounts were gone by then. The RN was running out of ships with enough space and weight allowance for a 16 ton mount- the carriers progressively lost their multiple bofors as various appendages were added (angled decks, mirror landing systems etc) to the extent that Victorious ended up with a single lonely sextuple mounting and Eagle got Sea Cat- as did Hermes in her 1964-66 refit (she had only ever had five twin bofors anyway). The battleships went in 1957 as did any chance of building a new gun-cruiser. That just left a diminishing fleet of legacy cruisers, the Tigers had the 3"/70 so didn't need bofors guns and all the others were to be gone by the mid-60s.

 

[Abraham Gubler]

On checking Friedman, the Bofors twin 57mm weighed 30 tons, the French one 16 tons. The RN Bofors Mk 5 water-cooled twin 40mm weighed 6.4 tons, the single air-cooled 40mm around 1.5 tons.

The image above indicates that the Vickers twin 57mm mounting is much smaller than the Bofors or French models. The Vickers design does not include reloading inside the gunhouse. It would appear that its radius and height would be about the same of the 40mm Mk 5. Weight would be higher but with the much smaller gunhouse weight should be less than the Swedish or French versions. Of course it couldn't replace the Mk 7/9 single barrel 40mm guns but it would appear to be a good fit for replacing the twin barrel 40mm/60 Mk 5 and as an alternative to the twin barrel 40mm/70 guns.

 

[Hot Breath]

Why are we discussing a naval weapon in the army section? Surely this discussion needs to be split?

 

[CJGibson]

Chaps,

I've looked at the original drawings and I have a spot of good news on the scale front.

The only dimensions I can see on Scheme 1 (or A on my drawing) with the upper gunner are: the radius from the gun muzzle (at zero elevation) to the centre of rotation of the turret - 14ft 6in (4.42m in proper money), 7ft 9in (2.36m) from the deck to the trunion centres and 14ft 2in (4.32m) from the deck to the top of the cupola.

I might add these to the drawing if I can find it again.

No such dimensions on Scheme 2 (lower gunner). I haven't drawn that as the Scheme 1 was a right PITA.

Hope this helps.

Chris