Sir John Valentine Carden Survives. Part 2.

[marathag]

Why can't the 75HV use 75x350 shells? As can a bored out 6 pdr. The Americans can build the 75HV under license instead of the 76mm M1

I'd hate to lose the 17 pdr but it seems like the sensible thing.

Move straight to 20 pdr?

Sensible? NIH mostly overrules that. 57mm M1 was greenlit as there was nothing else close In the pipeline.
Somewhat surprised that Ordnance never tried the lightweight T13E1 75 from the B-25 as a towed piece.
Similar weight and similar performance, plus able to fire all the different 75mm projectiles.
Instead, from 1942 McNair was pushing for the M5 3' gun that weighed almost 5000 pounds.
the PAK 40, was almost 2 foot lower in profile, and around a ton lighter, for same AP performance.

 

[vizzer]

No North Sea or Humber Estuary in the Yorkshire moors!

Almost like they didn't look out the windows & see they were over land rather than sea 😁

 

[diestormlie]

In 1939 when the Germans used the Graf Zeppelins as an ELINT platform to assess the UK Radar defence, they flew up the east coast of England tracked by Chain Home the whole way. Although the Germans were picking up the 12.5meter wave band transmitions from Chain Home they completely dismissed them as being evidence of a British Radar system as the wave length was much longer than any used by their own systems and their electronic experts deemed it technically inferior to any system they would contemplate building. Such is Military and Scientific Hubris !

Please explain the joke for those of us not wise in Radar Science. AKA me.

 

[Cymraeg]

That is an amazing anecdote. Thank you for sharing it!

RV Jones wrote a book about the electronic side of the war that I massively recommend. It's called 'Most Secret War', although I think that in the US it was called 'The Wizard War'.

 

[Peg Leg Pom]

Please explain the joke for those of us not wise in Radar Science. AKA me.

The Germans couldn't believe that someone would opt for a less than ideal solution that worked rather than a perfect solution that might work next year. They never seemed to grasp the concept of Good enough for now and we'll improve it later.

 

[Derek Pullem]

Please explain the joke for those of us not wise in Radar Science. AKA me.

Similar to Germany evaluation of an atomic bomb as scientifically impossible. Until the Americans built one.

Wavelength of Chain Home was 5 times that of Freya, the German air detection system and the Germans discounted the possibility of anyone using such an outdated system.

Of course outdated meant the British had already integrated into an air defence system and were able to use it properly. Unlike the Germans who took a while.

 

[pjmidd]

Similar to Germany evaluation of an atomic bomb as scientifically impossible. Until the Americans built one.

Wavelength of Chain Home was 5 times that of Freya, the German air detection system and the Germans discounted the possibility of anyone using such an outdated system.

Of course outdated meant the British had already integrated into an air defence system and were able to use it properly. Unlike the Germans who took a while.

Indeed, the British deliberately decided to use off the shelf components, hence the wavelength, specifically to get it into service ASAP. They did reject the German approach purely on the basis they decided they needed the system now , not in a year or two's time.

 

[AlanJWhite]

Please explain the joke for those of us not wise in Radar Science. AKA me.

The principle of Radar works with (almost) all types of radio signals, each type having pros and cons

Long wavelength i.e 10s of meters (which means a low frequency) was easier to build at the time
but is less accurate in estimating both direction and distance
AND requires a bulky antenna for transmission and reception

Hence the Nazis chose a shorter wavelength band and once they got it to work
could more easily build mobile stations unlike the British fixed towers used in Chain Home
but as others have written, CH and CH low-level were just ready in time

The further irony is that the British soon were building similar sets to the Nazis
and then far surpassed them by the so-called CENTIMETRE breakthrough that allow radar sets to see fine detail
(like map terrain from the air and detecting even a Uboat periscope)

When the Nazis captured the wreckage of such a device from a crashed plane near Rotterdam
Goering is said to have written that he knew Germany was no longer effective in the radar race

Though in truth it was American production capability that made the British device a game changer

 

[MarcH]

Why can't the 75HV use 75x350 shells? As can a bored out 6 pdr. The Americans can build the 75HV under license instead of the 76mm M1

I'd hate to lose the 17 pdr but it seems like the sensible thing.

Move straight to 20 pdr?

That was the plan for the OTL 75mm HV. I have had a strong suspicion about this for a long time and recently stumbled across this.

I recently assembled some information which was new to me about this obscure gun, so I thought it might be of interest to Tanknetters:



Vickers proposed the 75mm L/50 High Velocity tank gun early in 1942 as a replacement for the 6 pdr (57mm) gun. It was intended to be used in the Cromwell tank and six prototype guns were ordered in April 1943, but it was realised in the following month that it wouldn't fit in the Cromwell turret. Nonetheless, development was continued for the A34 Comet tank which was designed around the 75mm L/50. In October 1943 it was announced that the gun was to be modified to fire 17 pdr (76.2mm) projectiles, and a month later it was officially dubbed the 77mm. It entered service along with the Comet tank in December 1944 with the 11th Armoured Division in time to see action in World War 2, and was the best British tank of the war. 1,200 Comets were produced by the end of WW2 and it saw action in the Korean War before leaving British Army service in 1958. It saw service with five other countries and finally stopped being used in the 1980s. The Comet tank was the only user of the 77mm gun.

The original 75mm HV used the cartridge case of the 3 inch 20 cwt AA gun (developed in WW1, still in British service in WW2), necked down from 76.2mm to 75mm. The cartridge was intended to use US 75mm tank gun projectiles: the M61 APCBC (14.92 lbs) and the M48 HE (14.6 lbs) as used with a smaller cartridge case in the M2 and M3 tank guns (M3 and M4 tanks) and the M4 and M5 aircraft guns (B-25G/H). Muzzle velocity with the M61 was calculated to be 2,650 fps in a new gun (2,600 fps assumed in comparisons) compared with 2,030 fps in the M3 tank gun, but it was felt that the M48 shell wouldn't be able to tolerate such a high chamber pressure so it was downloaded to 1,500 fps (35,840 psi rather than 49,280 psi for the APCBC).

Estimated armour penetration figures for the 75mm HV firing an M61 projectile were prepared. These showed a figure of 87mm at 1000 yards/30 degrees compared with c.60mm for the M3 tank gun. The performance of the 75mm HV was therefore calculated to be about the same as the US 76mm tank gun, although the 75mm M48 HE shell was much more effective than the 76mm's M42.

The only difference between the 75mm HV and the production 77mm was the fractional difference in calibre: the 77mm cartridge case was therefore exactly the same as that for the 3 inch 20 cwt, although the projectiles were different and it was loaded to a much higher performance. The 77mm's APCBC projectile from the 17 pdr (which did actually weigh 17 lb) delivered far better penetration than the 75mm HV: 108 mm at 1000 yards/30 degrees. With APDS, penetration increased to 165mm. Conversely, the 77mm's HE shell (15.4 lb) was no better than the 76mm's (in both cases, they suffered from the thicker shell walls needed to resist the high pressures). Later HE shells for the 17 pdr/77mm were much more effective as they were loaded to a lower velocity and pressure, allowing thinner walled shells to be used.

It is not clear why Vickers decided to neck down the 3 inch 20 cwt case to take the US 75mm projectiles, before restoring it to the original 76.2mm calibre. 75mm was not a standard British calibre, whereas 76.2mm certainly was and had already been selected as the calibre for the 17pdr gun early in 1941, a year before the 75mm HV was proposed and several months before the US M3 tank (the first with a 75mm gun) entered service with the British Army. What's more, despite the extensive British use of M3 and then M4 tanks with 75mm guns it seems that 75mm ammunition was never manufactured in the UK (it all came from the USA) so there was no domestic source of 75mm projectiles.

This is by Tony Williams who should need no introduction. Original site is linked here. It basically explains why Britain was going to adopt a non standard calibre in the middle of the war. Particularly given that the 3" 20cwt AA gun had AP and HE shells available before the 75mm HV was proposed. The question was always why use the same case but a different projectile? this to me settles the argument.

 

[Bougnas]

That was the plan for the OTL 75mm HV. I have had a strong suspicion about this for a long time and recently stumbled across this.

This is by Tony Williams who should need no introduction. Original site is linked here. It basically explains why Britain was going to adopt a non standard calibre in the middle of the war. Particularly given that the 3" 20cwt AA gun had AP and HE shells available before the 75mm HV was proposed. The question was always why use the same case but a different projectile? this to me settles the argument.

What I find interesting is that the British didn't ask for 3" projectiles which should fit the 3" 20 cwt case just as well as 75, even though the Americans themselves preferred said projectile over using the 75mm for high velocity guns. Seems like there were some shenanigans at play between the two projectiles explaining how the US and UK chose different ones for fundamentally the same ballistics.

 

[Mark1878]

Similar to Germany evaluation of an atomic bomb as scientifically impossible. Until the Americans built one.

Wavelength of Chain Home was 5 times that of Freya, the German air detection system and the Germans discounted the possibility of anyone using such an outdated system.

Of course outdated meant the British had already integrated into an air defence system and were able to use it properly. Unlike the Germans who took a while.

Another one I think I saw in R.V.Jones's book, "Most Secret War"

Martin Ryle was in the war involved with radar (After the war he became a radio astronomer and later the Astronomer Royal and Nobel Prize winner) said that he could easily tell if a radar was British or German by checking its stability.

Ah I found the except and it also shows that British Experts could fall for the opposite bias to the Germans. If the electronics were sophisticated then it must be for special use

However, our experts concluded that it was not a simple radar system but one that was intended for precision long-range bombing, and they backed their argument by the fact that the radio frequency and the pulse repetition rate were far more stable than would be required for ordinary radar purposes, and would only be necessary where extremely accurate range determination was necessary, such as determining the absolute position of an aircraft relative to a ground target. By this time there was more than one Mammut on the Channel coast, and every one had this same stability. It was not easy to challenge the experts on matters of technical detail, when these were supported by rational argument, but I got them to agree that the ordinary Freyas were intended merely for radar and not for long-range bombing; I then asked them to go out and check how stable the Freyas were, because I suspected that the high stability that we had observed was merely another example of German thoroughness and precision, even where it was not required. A fortnight later the experts came back and told me that I was right: the stability of <a id="mos0001201"/>every German radar station was better than that of the best instruments that we had available to check them. In fact, Martin Ryle, afterwards to win a Nobel Prize for Radioastronomy, was one of our observers, and he told me that ever afterwards if he wanted to know whether a radar transmission was British or German, all he had to do was to check its stability.

 

[MattII]

Griffon itself would take more work than usual due to it having an integrated reductor unit for aircrafts, which needs to be deleted in tanks.
Considering Vickers' excellent relations with Ricardo and their push with diesel, it would rather make sense to use the dedicated H16 diesels that Ricardo developped in 1940/41 as an offshoot of the TOG program. It is not much larger than a Meteor but can do 720-760hp supercharged and 560 when naturally aspirated. Ricardo may even tune that engine specifically for a smaller "Vickturion" since TOG may not be as important ITTL.

I was kind of hoping for an engine with 800+ hp (or at least the ability to reach 800+ hp down the line).

It's also worth noting that a Vickers-designed Centurion stemming from the Valiant/Victor line wouldn't be anything like the offshoot of the A27/34 family designed by Leyland and co.
To start with it was a Heavy Cruiser while here it's actually related to an Infantry/borderline Universal family, which changes some specs. Second Vickers is more interested in diesel and a relatively more compact and weight-efficient vehicle. One could even contemplate a Vanguard-like pike nosed hull front. Turret design under Vickers was somewhat different.

Mm, the pike nose seems to be more complex for not overly much gain that I can see.

A lower weight means that Cent wouldn't necessarily be as underpowered as OTL.

An engine with more power at the baseline, and more growth potential would do that too.

 

[Bougnas]

I was kind of hoping for an engine with 800+ hp (or at least the ability to reach 800+ hp down the line).


Mm, the pike nose seems to be more complex for not overly much gain that I can see.


An engine with more power at the baseline, and more growth potential would do that too.

Best best is a supercharged Merlin or diesel then, the former was tried. 700, 900 or 1000hp was tested in a tank, 1000 started melting shit on Centurion because it was not well-designed for it. Both Sabre and Griffon have weird built-in reduction gearboxes that will be difficult to eliminate from a tank engine design. A completely rethought Meteor design (one that is not based on Merlin III) would get close, but is just as much work as the Sabre and Griffon adaptations.

The diesel I talked about would probably do 800+ late war or postwar anyway, since tank superchargers were still not fully developped and diesels were progressing quickly.

The reason I still think Centurion would be lighter in the first place is because getting it that heavy for the weight and actual space it offered required a high degree of weight/volume inefficiencies which stemmed from the A27/34 legacy (namely the very heavy wheels), something that Vickers is imo unlikely to match due to the current level of progression ITTL and due to greater experience/competence than Leyland and co.

 

[Llewwyy]

Best best is a supercharged Merlin or diesel then, the former was tried. 700, 900 or 1000hp was tested in a tank, 1000 started melting shit on Centurion because it was not well-designed for it. Both Sabre and Griffon have weird built-in reduction gearboxes that will be difficult to eliminate from a tank engine design. A completely rethought Meteor design (one that is not based on Merlin III) would get close, but is just as much work as the Sabre and Griffon adaptations.

The diesel I talked about would probably do 800+ late war or postwar anyway, since tank superchargers were still not fully developped and diesels were progressing quickly.

The reason I still think Centurion would be lighter in the first place is because getting it that heavy for the weight and actual space it offered required a high degree of weight/volume inefficiencies which stemmed from the A27/34 legacy (namely the very heavy wheels), something that Vickers is imo unlikely to match due to the current level of progression ITTL and due to greater experience/competence than Leyland and co.

How about an early RR Crecy? I think it was 2 stroke but perhaps Ricardo could convert it to diesel.

 

[ArtosStark]

The reason I still think Centurion would be lighter in the first place is because getting it that heavy for the weight and actual space it offered required a high degree of weight/volume inefficiencies which stemmed from the A27/34 legacy (namely the very heavy wheels), something that Vickers is imo unlikely to match due to the current level of progression ITTL and due to greater experience/competence than Leyland and co.

Any thoughts on how much lighter it could be? Centurion was over 50 tons. Could the Vickers effort be closer to 40? 45?

How about an early RR Crecy? I think it was 2 stroke but perhaps Ricardo could convert it to diesel.

The Crecy was originally mooted as a diesel and IIRC the first test cylinders were compression firing. So that part would probably be doable. That said, a high performance, sleeve valve, two stroke, high reving hyper engine, noted for its very loud running and that is still failing as many bench tests as it passes in 1944 is probably not the ideal tank engine.

 

[MarcH]

What I find interesting is that the British didn't ask for 3" projectiles which should fit the 3" 20 cwt case just as well as 75, even though the Americans themselves preferred said projectile over using the 75mm for high velocity guns. Seems like there were some shenanigans at play between the two projectiles explaining how the US and UK chose different ones for fundamentally the same ballistics.

Because Britain does not need a 3" shell, they have an AP shell for the 3" 20cwt and the 17pounder is basically right around the corner if they want a better 3" shell. Putting the 17pounder shell into the 420mm 3" 20cwt case is what they did after all for the 77mm HV. As for why Britain went the 75mm US shell route this is my speculation.

First some historical perspective. In 1942 Britain came quite close to stopping tank production altogether and just relying on American tanks. While there are certainly advantages to this, particularly given what tanks Britain is producing in 1942 there are also downsides for Britain. For one they basically loose all control over their tank arm. Now the tanks themselves are fine, the problem Britain probably has is with the gun. The US 75mm while very good at worst when first introduced it has limited potential to grow to face new threats. In addition relying wholly on the Americans will wound the pride somewhat. My theory therefore is that the 75mm HV was designed to appeal to the Americans. Offer them a gun that has all the benefits of the 75mm while improving on it's weakness, namely its limited top AP potential. That gives the British the tank they want with a better gun and saves a bit of national pride. The problem is that by the time the gun might be ready the Americans have pretty much moved on from listening to the British for good and ill. That is why the project ultimately died and not the fact it would not fit in the Cromwell. Had the Americans been willing to adopt it then the British would have stuck with it but given that they weren't then there is no need to stick with the non standard calibre.

 

[Bougnas]

Any thoughts on how much lighter it could be? Centurion was over 50 tons. Could the Vickers effort be closer to 40? 45?

If we compare specifically Mark II with the 17pdr to be fairer, that was 48 tons (48.9 for Mark III), then 45 (46 tonnes) should be achievable. 40 would require particular tricks that the British couldn't/wouldn't do at the time. 46 tonnes is doable if conservative because while it has a heavier turret and suspension (somewhat) than Panther which is 44.5, it was also supposed to have a smaller hull overall which should have been enough to get marginally heavier/equal weight (more compact powertrain, no driveshaft in middle so could be lower).

There is also the fact that even an hypothetical Pershing with 8" armor basis (thicker than Cent, with thicker sides in places, contemplated before T26E5) was 44 tonnes or less, even though it can carry a similarly large gun and has only a somewhat shorter and lighter powertrain. So Panther and Pershing both give good estimates for what a less inefficient Centurion should have weighed.

 

[MattII]

Best best is a supercharged Merlin or diesel then, the former was tried. 700, 900 or 1000hp was tested in a tank, 1000 started melting shit on Centurion because it was not well-designed for it. Both Sabre and Griffon have weird built-in reduction gearboxes that will be difficult to eliminate from a tank engine design. A completely rethought Meteor design (one that is not based on Merlin III) would get close, but is just as much work as the Sabre and Griffon adaptations.

The diesel I talked about would probably do 800+ late war or postwar anyway, since tank superchargers were still not fully developped and diesels were progressing quickly.

The reason I still think Centurion would be lighter in the first place is because getting it that heavy for the weight and actual space it offered required a high degree of weight/volume inefficiencies which stemmed from the A27/34 legacy (namely the very heavy wheels), something that Vickers is imo unlikely to match due to the current level of progression ITTL and due to greater experience/competence than Leyland and co.

Okay, that all sounds good and reasonable. Maybe start out with bigger gun too? Would the 3.7 inch AA gun be too much of a step up do you think?

 

[Bougnas]

Okay, that all sounds good and reasonable. Maybe start out with bigger gun too? Would the 3.7 inch AA gun be too much of a step up do you think?

Full power 37 and 32pdr would be a bit difficult, but 28pdr (17pdr rebored/rechambered for 3.7" and basically a US 90mm equivalent) was designed to be a straight swap with 17pdr so it would absolutely work, and a 3.7" between the two (like the 30pdr 3.7" which had a less potent projectile than the 37 or 32pdr), or the 30 pounder (87mm, same caliber as 25pdr but with a heavier projectile and 2600 fps velocity), both guns with intermediate ballistics, would probably be just fine.

 

[Thoresby]

Because Britain does not need a 3" shell, they have an AP shell for the 3" 20cwt and the 17pounder is basically right around the corner if they want a better 3" shell. Putting the 17pounder shell into the 420mm 3" 20cwt case is what they did after all for the 77mm HV. As for why Britain went the 75mm US shell route this is my speculation.

First some historical perspective. In 1942 Britain came quite close to stopping tank production altogether and just relying on American tanks. While there are certainly advantages to this, particularly given what tanks Britain is producing in 1942 there are also downsides for Britain. For one they basically loose all control over their tank arm. Now the tanks themselves are fine, the problem Britain probably has is with the gun. The US 75mm while very good at worst when first introduced it has limited potential to grow to face new threats. In addition relying wholly on the Americans will wound the pride somewhat. My theory therefore is that the 75mm HV was designed to appeal to the Americans. Offer them a gun that has all the benefits of the 75mm while improving on it's weakness, namely its limited top AP potential. That gives the British the tank they want with a better gun and saves a bit of national pride. The problem is that by the time the gun might be ready the Americans have pretty much moved on from listening to the British for good and ill. That is why the project ultimately died and not the fact it would not fit in the Cromwell. Had the Americans been willing to adopt it then the British would have stuck with it but given that they weren't then there is no need to stick with the non standard calibre.

That makes a lot of sense as mental process and fits with a lot of other projects the British looked at in that 41-43 period when quite what the division of labour in the Anglo-American partnership was being worked out.