An even greater inter-Allied cooperation on the technical & tactical matter?

Outright standardizing on certain parts or equipment is rather challenging since one country's tooling stock may not be suitable for its production, or because it's more convenient to keep producing the domestic designs even if they may be worse or redundant. Of course there are some instances where some standardization was done when one country had no equivalent (eg the US adopting the 6 pounder and 20mm Hispano albeit with several design changes). Design ideas seem easier to share.

I know that there was some thought into using a "Packard Meteor", a custom Packard tank engine or a variation of the Ford V12 on the A27 Cromwell which could have led to some standardization had such engines been used in Shermans (M4A4 chassis was mooted with the Ford V12) or T2X series as well. I'm afraid most of the other Wallied equipment runs into the issue of domestic designs already being in production for quite some time.

Interestingly enough, some promising co-op work went on during the limited timeframe the British and French fought together up to June 1940. Both parties were preparing to jointly run comparative test flights of their aircrafts. Some studies were done to evaluate the possibility of using one country's aircraft equipment (like gauges or navigation equipment) or sub-parts by the other. Assembly of US aircrafts for both countries was supposed to be done by one country per type, eg France was to expand its own assembly base (near Bourges IIRC) for Douglas and Curtiss aircrafts to meet joint needs, while Lockheed aircrafts were to be assembled in the UK.

One thing that could have happened on the co-op level if France had not fallen and the US industry had been called on to supply the Anglo-French, is the US standardizing on French 75mm AP ammunition and higher-powered 75mm guns. US 75mm AP ammo seems to have entered production no earlier than January 1942 while the French were in the process of industrializing modern AP (APCBC) in mid-1940; the 75mm M3 ballistics are extremely close to what was done 1-2 years before for the French 640 m/s class 75 guns (very similar bore length and charge characteristics). It would thus make sense that the US would piggyback off of already complete studies that would even have entered production early, with France probably having a sufficient lead in the production at this stage to set the standard for parts imported from the US. The British would probably have done the same regarding the OQF 75mm.

Elan Vital said:

One thing that could have happened on the co-op level if France had not fallen and the US industry had been called on to supply the Anglo-French, is the US standardizing on French 75mm AP ammunition and higher-powered 75mm guns. US 75mm AP ammo seems to have entered production no earlier than January 1942 while the French were in the process of industrializing modern AP (APCBC) in mid-1940; the 75mm M3 ballistics are extremely close to what was done 1-2 years before for the French 640 m/s class 75 guns (very similar bore length and charge characteristics). It would thus make sense that the US would piggyback off of already complete studies that would even have entered production early, with France probably having a sufficient lead in the production at this stage to set the standard for parts imported from the US. The British would probably have done the same regarding the OQF 75mm.

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Seems like the Allies were 'installing' the German 75mm AP shots on the US (French) 75mm ammo in North Africa, for the needs of their tanks. Rumor has it that Soviets were doing the opposite for the needs of the 6pdr gun from the LL - removing the AP shots and installing their own HE shells from the 57mm At gun.

Perhaps in the similar fashion the Soviet 76mm AP shots would've been a good fit for the US 76mm gun? If the French hold, their cored 37mm projectile adopted for the M4 gun on the P-39 would've been interesting.

(post-ww2, the ex-Yu military was modifying the American 90mm AP shots for the needs of the captured 88mm guns)

Howard Gibson said:

... The British installed R2800s in most of their Vickers Warwicks. The Warwick was big twin engined aircraft, and the Sabres and Centauruses simply were not available. I wonder how an R2800 would have worked on a Hawker Tornado or Tempest? The Fairey Barracuda was too big for its Merlin engine. Wright R2600 anyone? How about four R2800s on the Short Stirlings?

Did the British manufacture any American designs?

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The Australians put R-2600's in one Beaufighter but it took too long and was not considered worth repeating.

The Australians manufactured Pratt R-1340 and R-1830 engines under licence but I am not aware of any American engines manufactured in the UK.

In 1941 there was a plan to produce the Short Stirling in Canada powered by 1,600hp GR2600G-A5B engines. While the project fell through, two (or four?) aircraft were converted as prototypes in Britain. It also proposed the S.36 "Super Stirling" powered by 4xCentaurus engines to a 1941 Spec.

220 Wellington IV were built with 1,200hp P&W R-1830 Twin Wasp engines at the Broughton factory. This was intended as a protection against shortages of Pegasus engines for the Mk.I, Merlin X for the Mk.II and Hercules for the Mk.III.

The Beaufort was another to use the Twin Wasp in all the Australian production but also in the Mk.II produced in Britain (about 400 aircraft)

These engines were all imports.

There were 3 Stirling II prototypes, 165 Beaufort II and 250 T.II.

Warwick, ignoring prototypes, 16 B.I, 40 B(ASR).I, 14 C.I, 235 ASR.I, 100 C.III with R-2800, total 405, 118 C.II, 14 II (MET), 211 GR.V and 94 GR.VI, total 437 with Centaurus.

British Built Beaufighter Ic T4921/A19-2 After squadron service sent on 5 February 1943 to have R-2600 engines fitted, as an insurance against interruption of Hercules supply, the engines needed a new nacelle which extended beyond the wing trailing edge, as of 19 July 1944 it was at 1 Aircraft Performance Unit, with Wright engines, awaiting return of reconditioned fuel tanks and with cowl gill modifications proceeding. As of 20 September it was ready for the latest test flights, on 4 October 1944 a dihedral tail plane was being installed, in mid November undercarriage door modifications were being done, in January 1945 hydraulically operated undercarriage doors were being installed and so on. Australian Beaufighter production began in May 1944.

One - very cunning - plan would've involved the much greater effort towards the Merlin Mustang. Basically, something that is not perfect, but that is excellent in 3 things at least:
- available in good numbers for the air var in the ETO in 1943
- performance
- range

The 1st bullet point would've been achieved via making enough of Mustang X, and early, talk winter 1942/43 and in Spring of 1943. Airframes in question - whatever is survived among the Mustang I and Ia, plus the shipment of the new airframes from NAA. 2nd bullet point is easy - a combo between the 2-stage Merlin and the Mustang airframe = success. 3rd bullet point - additional fuel tankage in the place where the cameras were installed in the recon Mustangs; do the drop tank facility as soon as possible.

Shortcomings of the idea:
- supply of the 2-stage Merlins was not immense between the Autumn of 1942 and the same time of 1943, so there will be less of the Spitfire IXs manufactured (a trade off that I'm willing to accept)
- need for something to replace the recon Mustangs - stick the cameras on the A-36 and P-51As, ship these to the UK (come late 1943, supply of Mustangs is much improved, so the needs of 1944 tac recons can be fulfilled)

What can be gained? A much earlier attrition of the LW in the ETO, lower loss rate of the heavies turning this into a virtuous circle of ever bigger number of bombers making an even greater dent on the German war production and supplies. All P-38s from the UK can go to the MTO now.
Indirectly, this might've served as a template and impetus to have the P-47s, Spitfires and Tempests with increased fuel tankage, lest the laurels would've belonged to the Mustang only.

A more nerfed plan would've involved sticking the Merlin 45 and 50 (instead of the 60s) on the Mustangs.

tomo pauk said:

Seems like the Allies were 'installing' the German 75mm AP shots on the US (French) 75mm ammo in North Africa, for the needs of their tanks. Rumor has it that Soviets were doing the opposite for the needs of the 6pdr gun from the LL - removing the AP shots and installing their own HE shells from the 57mm At gun.

Perhaps in the similar fashion the Soviet 76mm AP shots would've been a good fit for the US 76mm gun? If the French hold, their cored 37mm projectile adopted for the M4 gun on the P-39 would've been interesting.

(post-ww2, the ex-Yu military was modifying the American 90mm AP shots for the needs of the captured 88mm guns)

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Soviet 76 ammo performed somewhat better than US 76 AP but it would probably be more practical and even better to standardize on 17pdr projectiles, or an extrapolation of French 75 APCBC for an earlier deployment.

France also had 90mm solid shot APCBC designed by 1940 so that would be an option for an early US 90 shot.

Correcting my previous reply, 640 m/s ballistics only matter if the French fielded tank or field guns with those, but in the case of field guns at least they were supposed to choose between 350R case at 640 m/s or 480R case at 700 m/s. The latter would be intermediary between the not-yet-in-existence 76 M1 and the US 75 M1897 pattern guns, but still requires a new cartridge case while not providing 3" gun ballistics.

Elan Vital said:

Correcting my previous reply, 640 m/s ballistics only matter if the French fielded tank or field guns with those, but in the case of field guns at least they were supposed to choose between 350R case at 640 m/s or 480R case at 700 m/s. The latter would be intermediary between the not-yet-in-existence 76 M1 and the US 75 M1897 pattern guns, but still requires a new cartridge case while not providing 3" gun ballistics.

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One wonders - how much hotter the French/US 75mm could've been loaded? It seems to me that many of the pre-1945 guns were over-built, at least when looking at barrels being over-bored, and/or the increse of the propelling charge.
A 75mm gun either loaded to, or modified to take the more powerful cartridge would not be unheard of; granted, it will require the muzzle brake to safely operate.

tomo pauk said:

One wonders - how much hotter the French/US 75mm could've been loaded? It seems to me that many of the pre-1945 guns were over-built, at least when looking at barrels being over-bored, and/or the increse of the propelling charge.
A 75mm gun either loaded to, or modified to take the more powerful cartridge would not be unheard of; granted, it will require the muzzle brake to safely operate.

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I've been trying to find exact equivalents to the US/French service pressure in other countries to see if there was room for improvement, to no avail but IIRC some Soviet high-velocity guns (57mm) and British 77/17 pdr work a step beyond the US and the French (more like 300-310 MPa instead of 290 MPa).

The French basically had 3 main levels of pressure, 240-250 MPa (75mm Mle 1897, mayyybe 47 SA35, 75mm Mle 1928 AA ballistics), 260-270 MPa (640 m/s class 75, 37mm SA38) and 290 MPa (700 m/s class 75, 47mm casemate and SA37). The US 3" M7 sits in the 1st category, the 75 M3 in the 2nd and the 76 in the 3rd category (the 90 if I recall started in 2nd and then was upped to third category with higher velocity late M82 ammo). 76 was maybe used at 310 MPa service pressure.
The max they gave for the 75mm 350R cartridge at 270 MPa was 652 m/s in a gun a little longer than the US 75 M3, so that gives an idea of the max here. I'm not sure how much of the 700 m/s gun's extra velocity was down to the higher pressure, and how much was down to the increased propellant load. Nor if one could even up the pressure on 350R cartridges.

That said, reportedly the BAS microfilms from WW2 said that 75mm M3 could have been hotloaded from the regular 2030 fps to 2300 fps (about 700 m/s).

The postwar 90mm T119 (M36/M41) had a rated max pressure of 47k psi or 324 MPa, but not sure if this is the same thing that is being discussed here.
I think there is some leeway overall, but not sure how much.

3 things with upgrading guns.
1, chamber pressure.
2, expected barrel life.
3, recoil system.

Muzzle brakes allow for increased performance using an existing recoil system. They do nothing for either barrel life or safe chamber pressure.
Safe chamber pressure was sometimes achieved using newer propellents.
Better materials (steels) allowed for more pressure for the same weight with both safety and barrel life.
US 3in/76mm is a classic. Gun barrel got a lot lighter. Powder charge got smaller with new propellent. External ballistics stayed the same.

We can probably expect that the hotter rounds will represent perhaps 10% of what would've been fired from the French 75 in the ww2 scenarios?

There is also another arithmetic, covering the decreased barrel life of a 25+- years old gun vs. the consequences of the enemy tanks breaching the line and wreaking havoc in the rear area, with possibility of inciting panic among the inexperienced soldiers, because the AT guns cannot perform as they should. Sorta like rather loosing the chess mach because of not wanting to loose a pawn.

I will note that the French 640 m/s guns used new barrels (IIRC this was also done to improve other aspects such as quick barrel removal). The M3 75mm also involves a new barrel though I'm not sure it was itself an enabler for the extra pressure and seemingly it didn't have the rifling, chamber mouth and driving band modifications of the French guns.

Hot loading without modifications on the gun's end wasn't common in France. Going from the 690 m/s of the 47mm Mle 1902 to the 855 m/s of the Mle 1934/SA 37 took deeper rifling grooves and a slight modification to the case profile. New ammo on SA16/18 short guns (subcaliber and new HE) made a stronger case ejector useful (otherwise the case would not eject as intended). You know about the 75s, and they also required a higher capacity recuperator. Granted, this was before the real heyday of hot loading (1942-1945).

tomo pauk said:

One - very cunning - plan would've involved the much greater effort towards the Merlin Mustang. Basically, something that is not perfect, but that is excellent in 3 things at least:
- available in good numbers for the air var in the ETO in 1943
- performance
- range

The 1st bullet point would've been achieved via making enough of Mustang X, and early, talk winter 1942/43 and in Spring of 1943. Airframes in question - whatever is survived among the Mustang I and Ia, plus the shipment of the new airframes from NAA. 2nd bullet point is easy - a combo between the 2-stage Merlin and the Mustang airframe = success. 3rd bullet point - additional fuel tankage in the place where the cameras were installed in the recon Mustangs; do the drop tank facility as soon as possible.

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Are we modifying existing Mustangs, or manufacturing them outright? Manufacturing stuff under license, especially foreign designed stuff, is not trivial. Obviously, quite a bit of this happened during WWII. I suppose North American should ship airframes without engines. How do the original radiators work with Merlins at high altitude

tomo pauk said:

A more nerfed plan would've involved sticking the Merlin 45 and 50 (instead of the 60s) on the Mustangs.

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The Merlin 45 was a horrible compromise that allowed Supermarine to use the Mark I and II style airframes on the Spitfire_Vs. We want two-speed superchargers at the very least on anything that can fit it. Merlin_XXs please. This is what they installed in P40s.

Howard Gibson said:

Rolls Royce was an artisanal outfit too. Both Ford of England and Packard in the USA told Rolls Royce that their drawings were crap. Mass production needed way more precision than Rolls Royce was calling up. I recently did a presentation on Design for Manufacture and Assembly (DFMA) and documentation, and I pointed out that the complete drawings of the strategically critical Merlin engines were done at least three times.

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People don't seem to like my post here. Production oriented automotive firms were not impressed with the documentation and organization of aerospace companies. This is true of Ford and England and Packard of USA making Rolls Royce engines, and it is true of Ford of USA when they manufactured Consolidated B24s. I am an old mechanical designer, and I am proud of my drafting skills. I don't hesitate to tell people that my drawings are better than everyone else's

Here is the Merlin production from one of Bill Gunston's books...


Rolls Royce and Consolidated made lots of Merlin engines and B24 Liberators. Did they do it as efficiently as the automotive firms?

This a bit off topic, but I am curious about how they managed to build 11,462 Vickers Wellingtons. In the 1930s, the geodetic construction was considered to be too expensive for civilian use, and only suitable for the military. A lot of work was put into making it manufacturable. There is a great documentary about building a Wellington in 24 hours, but the geodetic construction is pre-fabricated.

Howard Gibson said:

Are we modifying existing Mustangs, or manufacturing them outright? Manufacturing stuff under license, especially foreign designed stuff, is not trivial. Obviously, quite a bit of this happened during WWII. I suppose North American should ship airframes without engines. How do the original radiators work with Merlins at high altitude

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Existing surviving Mustangs I, in the UK.
2nd source are the engine-less airframes coming from NAA.

Howard Gibson said:

The Merlin 45 was a horrible compromise that allowed Supermarine to use the Mark I and II style airframes on the Spitfire_Vs. We want two-speed superchargers at the very least on anything that can fit it. Merlin_XXs please. This is what they installed in P40s.

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There was no Merlin 45 to be installed on the P-40s, unless the Spitfires get them; Merlin XX equivalent was what was made at Packard.
Merlin 45 was an excellent compromise, that was making the same power above ~10000 ft as the Merlin XX, while being cheaper and faster to make, and also lighter and a bit smaller. Spitfire V was 20 mph faster than the similar Mk.II counterpart (provided the same level of equipment, pit & finish).
2 speed superchargers are red herring here.

The 20 series Merlins were much better as the 'bomber engines'.

Howard Gibson said:

People don't seem to like my post here. Production oriented automotive firms were not impressed with the documentation and organization of aerospace companies. This is true of Ford and England and Packard of USA making Rolls Royce engines, and it is true of Ford of USA when they manufactured Consolidated B24s. I am an old mechanical designer, and I am proud of my drafting skills. I don't hesitate to tell people that my drawings are better than everyone else's

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People don't like that post of yours for the good reason - it does not stand up the scrutiny.
RR were series- and mass-producing the Merlin before a new factory was built for the production of Merlins, the factory in question being run by Ford. RR-run factories probably produced more Merlins than what the German factories produced Jumo 211s and DB 601s combined, even before the German factories were bombed. Apart from the propeller spline (designed for the US props) and the S/C drive (Wright instead of Farman type), parts were interchangable between the UK- and Packard-built Merlins.

You don't need to take my word for it, ask Calum Douglas (he posts on the Twitter and on the secretprojects forum), or see his posts here (link).

tomo pauk said:

Existing surviving Mustangs I, in the UK.
2nd source are the engine-less airframes coming from NAA.



There was no Merlin 45 to be installed on the P-40s, unless the Spitfires get them; Merlin XX equivalent was what was made at Packard.
Merlin 45 was an excellent compromise, that was making the same power above ~10000 ft as the Merlin XX, while being cheaper and faster to make, and also lighter and a bit smaller. Spitfire V was 20 mph faster than the similar Mk.II counterpart (provided the same level of equipment, pit & finish).
2 speed superchargers are red herring here.

The 20 series Merlins were much better as the 'bomber engines'.

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The Merlin XX improvements were mostly an improved impeller, and a two-speed drive. This was installed in Hurricanes, where they improved performance. The new engine did not fit in current Spitfire airframes, so they developed the single-speed Merlin_45 with the new impeller. If the Spitfire_III had reached production, it would have used the Merlin_XX. The Spitfire_V was significantly faster than a Spitfire_II mostly at altitude. A Merlin_XX equipped Hurricane_II was almost as fast as a Spitfire_V below 10,000ft.

The Merlin_45's advantage was that it fit in Spitfire_Vs, and it was better than the Merlin_XIIs used on Spitfire_IIs. If the two-speed supercharger fits, I want a two-speed supercharger.

Apparently, some later Hurricanes were equipped with the cropped supercharger single-stage Merlin_32s. Has anyone seen performance figures for these?

Howard Gibson said:

The Merlin XX improvements were mostly an improved impeller, and a two-speed drive. This was installed in Hurricanes, where they improved performance.

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The Merlin XX (and 45) differed from the Merlin X by having the much better air intake.
The Merlin X was the 1st to get the improved impeller.
The two-speed drive was beneficial for the low-altitude power, a thing immaterial for the fighters' air combat in the ETO, especially if one wants to defend the Allied bombers.

It is only to be expected that the Hurricane with the Merlin XX will be with the improved performance, the engine power above 10000 ft went up by 20%.

Howard Gibson said:

The new engine did not fit in current Spitfire airframes, so they developed the single-speed Merlin_45 with the new impeller. If the Spitfire_III had reached production, it would have used the Merlin_XX.

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The Merlin XX fit on the Spitfire. Both on the Spitfire III prototypes, that started the life as Spitfire I on the production line and were modified into the Mk.III, and as the retrofit on some Mk.IIs used by Coastal Command. Griffon with the 2-speed S/C fit on the Spitfire, the Merlin 60 and 70 series fit (together with their 2-speed 2-stage S/Cs), and so did the 2-stage Griffons.

But I guess some myths are still alive 80 years after the fact.

Howard Gibson said:

The Spitfire_V was significantly faster than a Spitfire_II mostly at altitude. A Merlin_XX equipped Hurricane_II was almost as fast as a Spitfire_V below 10,000ft.

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It is the altitude we're interested in here, not what the Merlin-powered Mustang can do at 5000 ft.

Allison engined Mustangs were prized by RAF low level tactical PR squadrons in NW Europe and the RAF scoured their holdings to keep Allison engined PR Mustangs in service right up to the end of the war. At sea level little could touch it for speed. They would be very unhappy with them being taken away to have Merlins fitted and used as fighters. They did make enquiries as to whether they could have new Allison engined Mustangs sent over in lieu of some Merlin ones but the production lines had gone over exclusively to Merlin Mustangs. At any higher levels the Merlin was better of course.

yulzari said:

Allison engined Mustangs were prized by RAF low level tactical PR squadrons in NW Europe and the RAF scoured their holdings to keep Allison engined PR Mustangs in service right up to the end of the war. At sea level little could touch it for speed.

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All true.

yulzari said:

They would be very unhappy with them being taken away to have Merlins fitted and used as fighters.

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Military people are not 8 year old girls or boys. Their happiness is not a thing.