The Franco-Belgian front holds 1940: consequences for the RAF?

[Elan Vital]

Hi everyone,

I tend to be quite interested in discussing the details of a scenario where the Entente holds the front near the Franco-Belgian border in 1940 (mostly in other forums).

I was now wondering what the impacts would be for the RAF.

Obviously we may see fewer American aircrafts in service in the RAF owing to France keeping her orders and taking some of the American production capacity - unless continued French funding through the Anglo-French Purchasing Commission further accelerates the American industrial buildup.

In operational terms, there is obviously the huge difference of some of the RAF staying in France and thus operating closer to German targets, but with temporarily worse conditions than in the UK (less developped radar network), while the British Isles themselves may see far fewer German air attacks; and the AdA participating in the air war so that the RAF will never be alone for one year like it was IRL until the USSR and the US got involved.

But in terms of British procurement and technical development, would we see any significant changes from OTL?

While Franco-British synergies were a real thing in other areas, France doesn't appear to have anything to offer to the UK other than the swirl throttle technology (Szydlowski-Planiol supercharger), which the British already witnessed in later German aircrafts but didn't use; some Merlin cooling system test data (a French Merlin-equipped Amiot 356 bomber was meant to fly to Derby in May 1940 for study as its cooling system was allegedly showing interesting performance compared to Hurricane and Spitfire cooling systems); and somewhat faster 20mm HS-404 autocannon development.

Meanwhile, the reasoning for British air-industrial choices also don't really change and some decisions were already taken even before May 1940: the doomed Whirlwind/Peregrine program, the cancellation of many Rolls-Royce engine projects in favor of focusing on the Merlin, the airframe choices themselves.

Does somebody here have some insight about British decisions which were more directly influenced by the French defeat and may genuinely not have happened without it?

 

[tomo pauk]

While Franco-British synergies were a real thing in other areas, France doesn't appear to have anything to offer to the UK other than the swirl throttle technology (Szydlowski-Planiol supercharger), which the British already witnessed in later German aircrafts but didn't use; some Merlin cooling system test data (a French Merlin-equipped Amiot 356 bomber was meant to fly to Derby in May 1940 for study as its cooling system was allegedly showing interesting performance compared to Hurricane and Spitfire cooling systems); and somewhat faster 20mm HS-404 autocannon development.

The S-P adjustable vanes were a good thing for improving the low-altitude power (same as with the swirl throttle by Polikovsky as installed on the Mikulin engines of ww2). If one has 2-speed S/C, appeal of the adjustable vanes is as good as lost, since the low-speed gearing takes care of the low-alt power. Doubly so if one has an basically unrestricted access to the high-octane fuel to further increase the boost as altitude is lower for greater power. Add the probably best S/C of 1940, as installed on the 2-speed supercharged Merlin XX, and there is not that much - if anything - that RR can learn.

Bristol might learn a thing or two from the S/C installed on the G&R 14R - still a 1-stage 2-speed device, but providing the altitude power no worse than BMW 801 despite the 14R being ~200 kg lighter engine.

The faster HS 404 development is certainly a boon; combined with no BoB as we know it might yield the much incresed might've.

Meanwhile, the reasoning for British air-industrial choices also don't really change and some decisions were already taken even before May 1940: the doomed Whirlwind/Peregrine program, the cancellation of many Rolls-Royce engine projects in favor of focusing on the Merlin, the airframe choices themselves.

Does somebody here have some insight about British decisions which were more directly influenced by the French defeat and may genuinely not have happened without it?

With France and Belgium holding out, British can press on with Spitfire III, thus negating much of problems that German fighters of 1941 brought. Peregrine was slated for cancellation due to the engine not being really mass-produced, so the price of engine was supposedly greater than that of the Merlin.

Defiant might get a bit longer life as a day fighter?

French defeat and the imminent invasion that never happened probably had a lot more importance on the tanks and anti-tank guns? A big change might be the lack of lend-lease law in the USA, but that is mostly taking effect in 1941.

 

[Rule of cool]

Interesting premise, however I'd point out that by 1918 both sides had learned how to break into and through extensive trench defences. So holding the Germans at the Belgian border won't mean settling in for years, it will only be until the next offensive that even in failure could advance 100km.

That does mean France fights on though, so I could imagine the RAF becoming more of a tactical force, rather than the strategic force it became. Also without the bases on the French Atlantic coast the uboats won't be much of a strategic threat. I suspect more medium bombers and fighter bombers will be produced and there would be prolonged campaigns to gain even local air superiority. I think fighters would get longer range pretty quickly, because being to close to the front line would leave their bases vulnerable to land offensives.

 

[Elan Vital]

The S-P adjustable vanes were a good thing for improving the low-altitude power (same as with the swirl throttle by Polikovsky as installed on the Mikulin engines of ww2). If one has 2-speed S/C, appeal of the adjustable vanes is as good as lost, since the low-speed gearing takes care of the low-alt power. Doubly so if one has an basically unrestricted access to the high-octane fuel to further increase the boost as altitude is lower for greater power. Add the probably best S/C of 1940, as installed on the 2-speed supercharged Merlin XX, and there is not that much - if anything - that RR can learn.

With France and Belgium holding out, British can press on with Spitfire III, thus negating much of problems that German fighters of 1941 brought. Peregrine was slated for cancellation due to the engine not being really mass-produced, so the price of engine was supposedly greater than that of the Merlin.

Defiant might get a bit longer life as a day fighter?

This is certainly true when comparing 2-speed Merlin XX or 61 to the single speed S39H3 S-P. My understanding is that a 2-speed swirl throttle would still improve performance a bit outside of the two rated altitudes, but I suppose the benefit would not really be worth the extra effort especially when production of the swirl throttle has not been prepared long in advance?

At the same time, if I go by the Secret Horsepower Race, integrating the two-speed Merlin into the Spitfire III still proved difficult even as of late 1940, so wouldn't the British still need the single-speed Merlin 45? In that case, the swirl throttle might be worth it. But given that coop on this regard still wasn't a thing as of mid-1940, maybe it was already too late to attempt a combined single-speed swirl throttle Merlin?

As for the other high alt French supercharging setups for inline engines (the 3-stage Farman/NC and the Hispano-Rateau or Hispano-Brown-Boveri turbochargers), they were probably only suitable for niche aircrafts.

Arguably, it might be perhaps easier to apply the swirl throttle supercharger to V-1710 rather than the Merlin? The French have more influence over the V-1710 owing to their large orders, and its supercharger itself is in greater need of upgrades than the Merlin.

Bristol might learn a thing or two from the S/C installed on the G&R 14R - still a 1-stage 2-speed device, but providing the altitude power no worse than BMW 801 despite the 14R being ~200 kg lighter engine.

There is probably some value in studying the GR 14R's supercharger for Bristol, if its design was truly as good as it is believed. Too bad GR superchargers are extremely obscure.

The faster HS 404 development is certainly a boon; combined with no BoB as we know it might yield the much incresed might've.

AFAIK the British wasted a lot of time working on a different belt feed than the French had been developping for the 20mm, so certainly beneficial. There are also claims of joint Anglo-French production of a 12.7 or 13.2mm Browning, so maybe France holding would keep this scheme alive.

I wonder if the Westland Whirwind would at least have had a more interesting operational life? The short range would be mitigated in France and it could be an especially useful boon in the air war over France and against any German bombing campaign of the French industry. The fighting altitude might be slighly more favourable than over Britain/the Channel as well.

French defeat and the imminent invasion that never happened probably had a lot more importance on the tanks and anti-tank guns? A big change might be the lack of lend-lease law in the USA, but that is mostly taking effect in 1941.

Regarding ground weapons, true, the Franco-British synergies are both better known and more significant than in the air war.
The French were already delivering a decent number of 25mm AT guns to the BEF (among other weapons) and were set to deliver 100 47mm guns per month starting from late 1940, which would largely help the British. The British were also set to imminently deliver up to 80 H39 tank castings per month for the French industry, in exchange for some B1 Bis tanks starting from July, and a proportion of H39 later in 1940 to accelerate the expansion of the BEF.

Naturally, French supply of antitank guns relieves the British industry for further upgrades, while British supply of armor plate/castings was explicitly intended to free up French armor steel capacity for an even greater expansion of their battle tank production program (B1 and successors).

Interesting premise, however I'd point out that by 1918 both sides had learned how to break into and through extensive trench defences. So holding the Germans at the Belgian border won't mean settling in for years, it will only be until the next offensive that even in failure could advance 100km. I think fighters would get longer range pretty quickly, because being to close to the front line would leave their bases vulnerable to land offensives.

This is true, but the next offensive can only happen so soon after the previous one. As is even IRL Case Yellow and Red inflicted severe losses on the German mechanized branches (ground and air), while depleting the ammunition reserves needed for breakthroughs, which limits the 1940 campaign season to about July at the latest until the weather becomes unfavourable. For the next campaign season of Spring 1941, it is the Entente which is somewhat more favoured given the industrial situation.

So the front would not be stable for years...but not necessarily in a good way for the Germans.

That does mean France fights on though, so I could imagine the RAF becoming more of a tactical force, rather than the strategic force it became. Also without the bases on the French Atlantic coast the uboats won't be much of a strategic threat. I suspect more medium bombers and fighter bombers will be produced and there would be prolonged campaigns to gain even local air superiority.

Didn't the British already intend to replace their medium bombers (Hampden, Whittley and others) with heavy ones in 1940? I don't recall any medium bomber successors in development even before May 40.
It's also worth noting that the British had launched a bombing campaign against German fuel industry and supplies in May 1940. With a better situation in France, it might actually grow into a larger and longer joint campaign while the stable front until Spring 1941 would not really promote a more tactical force, though the RAF would obviously have to be more balanced than IRL with a big ground front.

 

[DWG]

Regarding ground weapons, true, the Franco-British synergies are both better known and more significant than in the air war.
The French were already delivering a decent number of 25mm AT guns to the BEF (among other weapons) and were set to deliver 100 47mm guns per month starting from late 1940, which would largely help the British.

The 25mm ATG was inferior to the 2 Pdr, which was what British units should have had, but where they couldn't scale up production fast enough to ensure every BEF unit met its TOE, so France stepped in with the 25mm. Not sure which is superior wrt the 47mm APX and the 2 Pdr, but the French 75mm TAZ would definitely outperform both, especially with Brandt's DS round, and would become available if the line held. For the UK, not facing the losses of Dunkirk would mean the 6 Pdr could enter service on schedule, rather than being deferred for continued 2 Pdr production.

Didn't the British already intend to replace their medium bombers (Hampden, Whittley and others) with heavy ones in 1940? I don't recall any medium bomber successors in development even before May 40.

There were at least five. The Manchester and HP.56 were originally intended as medium twins to P.13/36, but ended up as the Lancaster and HP.57 Halifax for various reasons. The Albemarle is effectively a medium bomber, though a compromised one by the decision to focus on non-strategic materials. The Warwick was a scaled up Wellington delayed by issues with the Vulture and Sabre, and the Blenheim replacement Beaumont ended up inflated into the Bristol Buckingham.

 

[Rule of cool]

The example I would use is what the British did in the Med in 1941-43.

Fighting the real war, as opposed to planning with interwar theories tinged with the need to maintain budgets and independence through 2 lean decades, commanders in the Med didn't try to ramp up a strategic air campaign. With men, tanks and ships in contact with the enemy they had to do what worked, so focused on interdiction and attacks on base areas rather than trying to knock out Italian factories, oil refineries or other industrial targets.

In Britain, after the Blitz ended and Barbarossa started the RAF didn't have a lot of work to do so had the luxury to blunder blindly around Germany at night dropping bombs nowhere near their targets. However with an active front in France that luxury wouldn't exist, Bomber Command would have to support the Army like they did after Dunkirk by bombing German invasion barges and in 1944 by prepping northern France for invasion.

 

[Archibald]

A blunted sickle (,pdf27 at ah.com)

 

[Justo Miranda]

Hi everyone,

I tend to be quite interested in discussing the details of a scenario where the Entente holds the front near the Franco-Belgian border in 1940 (mostly in other forums).

I was now wondering what the impacts would be for the RAF.

Obviously we may see fewer American aircrafts in service in the RAF owing to France keeping her orders and taking some of the American production capacity - unless continued French funding through the Anglo-French Purchasing Commission further accelerates the American industrial buildup.

In operational terms, there is obviously the huge difference of some of the RAF staying in France and thus operating closer to German targets, but with temporarily worse conditions than in the UK (less developped radar network), while the British Isles themselves may see far fewer German air attacks; and the AdA participating in the air war so that the RAF will never be alone for one year like it was IRL until the USSR and the US got involved.

But in terms of British procurement and technical development, would we see any significant changes from OTL?

While Franco-British synergies were a real thing in other areas, France doesn't appear to have anything to offer to the UK other than the swirl throttle technology (Szydlowski-Planiol supercharger), which the British already witnessed in later German aircrafts but didn't use; some Merlin cooling system test data (a French Merlin-equipped Amiot 356 bomber was meant to fly to Derby in May 1940 for study as its cooling system was allegedly showing interesting performance compared to Hurricane and Spitfire cooling systems); and somewhat faster 20mm HS-404 autocannon development.

Meanwhile, the reasoning for British air-industrial choices also don't really change and some decisions were already taken even before May 1940: the doomed Whirlwind/Peregrine program, the cancellation of many Rolls-Royce engine projects in favor of focusing on the Merlin, the airframe choices themselves.

Does somebody here have some insight about British decisions which were more directly influenced by the French defeat and may genuinely not have happened without it?

In my opinion the question is simple: the Allies expected a war of attrition based on enormous amounts of artillery, replacing the trenches with the Maginot Line. The plan was to hold out until the naval blockade forced the Germans to ask for an armistice. When the Panzers found themselves on the other end of the line and with the Luftwaffe achieving air superiority thanks to the new Bf 109 E, panic set in and politicians went into shock, blaming each other for cowardice. The deadly mistake was not to continue the construction of the Maginot Line to the sea, a political stupidity so as not to isolate Belgium.

 

[DWG]

A blunted sickle (,pdf27 at ah.com)

There's also La France Continue*, where France falls but the French fight on from North Africa. See here for links.

* And APOD, which forks off from the La France Continue timeline.

 

[pathology_doc]

At the same time, if I go by the Secret Horsepower Race, integrating the two-speed Merlin into the Spitfire III still proved difficult even as of late 1940, so wouldn't the British still need the single-speed Merlin 45?

I have always wondered why Supermarine had so much trouble doing that and so little trouble integrating the Merlin 61 into an interim lash-up?

 

[Elan Vital]

Not sure which is superior wrt the 47mm APX and the 2 Pdr, but the French 75mm TAZ would definitely outperform both, especially with Brandt's DS round, and would become available if the line held. For the UK, not facing the losses of Dunkirk would mean the 6 Pdr could enter service on schedule, rather than being deferred for continued 2 Pdr production.

The 75mm TAZ was however not suitable as a common light/medium antitank gun like the 2/6pdr and 47mm. The French were rather explicit in the fact that their production capacity for medium calibre guns (75 and up) was limited, with the 75mm TAZ also being a heavy asset which would fit a different role, more like the 17 pdr. So for the UK, the step-up from the 2pdr will remain the 6pdr when it becomes available, and the 47mm in the interim/as a supplement until 6pdr production picks up enough.

There were at least five. The Manchester and HP.56 were originally intended as medium twins to P.13/36, but ended up as the Lancaster and HP.57 Halifax for various reasons. The Albemarle is effectively a medium bomber, though a compromised one by the decision to focus on non-strategic materials. The Warwick was a scaled up Wellington delayed by issues with the Vulture and Sabre, and the Blenheim replacement Beaumont ended up inflated into the Bristol Buckingham.

Interesting. In practice for this scenario, the HP 56 had already morphed into the HP 57 before 1940 and the odds of the Vulture being supported remain low. The Albemarle was apparently not performing well-enough to remain as a bomber, leaving the Warwick which was facing shortages of engines (and with France still there to go after the R-2800s the Warwick got, competition for the engine will be even more severe!); and the Buckingham which was apparently very late.

So it seems that the industrial situation by mid 1940 already condemned British medium bombers until 1943 at best, unless they reprioritize engines for them.

The French were in the opposite situation, not being able to expect domestic heavy bombers until late 1941 at the earliest, but working towards a medium bomber fleet.

I have always wondered why Supermarine had so much trouble doing that and so little trouble integrating the Merlin 61 into an interim lash-up?

@pathology_doc Ditto, the Spit IX ended up fitting it with a longer nose (and obviously some counterweight was needed). One can only assume that the British were so desperate to limit production line changes that they preferred keeping the short nose for the Spit V, requiring the Merlin 45. But if you need some change for the engine line to produce the new supercharger, wouldn't there be excess airframe production that you can afford to cut anyway?

 

[tomo pauk]

This is certainly true when comparing 2-speed Merlin XX or 61 to the single speed S39H3 S-P. My understanding is that a 2-speed swirl throttle would still improve performance a bit outside of the two rated altitudes, but I suppose the benefit would not really be worth the extra effort especially when production of the swirl throttle has not been prepared long in advance?

S/C on the Merlin 61 was not only with 2-speed gear, but it was also of the 2-stage version, that greatly improved power above 20000 ft.

At the same time, if I go by the Secret Horsepower Race, integrating the two-speed Merlin into the Spitfire III still proved difficult even as of late 1940, so wouldn't the British still need the single-speed Merlin 45? In that case, the swirl throttle might be worth it. But given that coop on this regard still wasn't a thing as of mid-1940, maybe it was already too late to attempt a combined single-speed swirl throttle Merlin?

Integration of the 2-speed Merlin (the Mk.XX) went as good as possible on the Spitfire III; later (1942) one of the prototypes even received the 2-stage Merlin 61. Problem was that the Mk.XX was required for the Hurricane II in order to cancel out the performance advantage possessed by the Bf 109E, so Spitfires gotten the Merlin XII (as well as the improved protection) becoming Spitfire II.
Yes, the swirl throttle would've been good for the 1-speed Merlin 45, that lacked the low gear for it's S/C. Note that both Merlin 45 and XX were outfitted with much better superchargers than it was the case with Merlin III or the XII.

It was probably too bad that Spitfire III was not outfitted with Merlin XII, in order to take advantage of it's aerodynamic improvements (internal BP glass, fully covered wheel wells, retractable tailwheel) - perhaps resulting in a 370+ mph fighter for BoB? Increased fuel tankage would've also come in handy.
Later (1941) move to Merlin 45, for another 15+- mph?

Arguably, it might be perhaps easier to apply the swirl throttle supercharger to V-1710 rather than the Merlin? The French have more influence over the V-1710 owing to their large orders, and its supercharger itself is in greater need of upgrades than the Merlin.

Supercharger of the V-1710 (without talking about the turbo versions) needed improvements for it's power at higher altitudes, that was lacking due to the too small impeller rotating at modest speeds. Swirl throttle can bring the improvement at lower altitudes, but not at higher altitudes.

There is probably some value in studying the GR 14R's supercharger for Bristol, if its design was truly as good as it is believed. Too bad GR superchargers are extremely obscure.

This is the only data from a primary source that I'm aware of the 14R: link
Making 1320 PS at almost 6 km, and that is the 30 min rating (ie. still not the best available power setting) was better value than what the fully-rated BMW 801D did in late 1942 and on. Bristol Hercules engines managed to beat this by late 1944, after the full redesign of the S/C - so certainly there is something to learn here.

Naturally, French supply of antitank guns relieves the British industry for further upgrades, while British supply of armor plate/castings was explicitly intended to free up French armor steel capacity for an even greater expansion of their battle tank production program (B1 and successors).

Without the invasion scare, the 6pdr would probably see the combat as early as late 1940, and certainly by early 1941.

Didn't the British already intend to replace their medium bombers (Hampden, Whittley and others) with heavy ones in 1940? I don't recall any medium bomber successors in development even before May 40.

British regarded the Whitley and Wellington (and maybe Hampden) as heavy bombers, while the Blenheim (and Battle, and later Mosquito) were called the light bombers; yes, indeed, RAF was moving onto 4-engined bombers already by 1940, with some 2-engined designs also in pipeline.
As noted above, serious problems with 2000+ HP British engines relegated these 2-engined bombers into non-starters for the intended role.

Fighting the real war, as opposed to planning with interwar theories tinged with the need to maintain budgets and independence through 2 lean decades, commanders in the Med didn't try to ramp up a strategic air campaign.

Not having a sizable force of heavy bombers, and not having enemy industry in range for day-after-day bombing kinda puts the stops on the attempt for a strategic air campaign

 

[tomo pauk]

I have always wondered why Supermarine had so much trouble doing that and so little trouble integrating the Merlin 61 into an interim lash-up?

There was no trouble in installing the Mk.XX on the Spitfire III.
Trouble was the lack of Mk.XXs both for Spitfire and Hurricane, the later needing it much more than the former.

 

[Scott Kenny]

On the ground side, the change to the 6pd as originally planned would greatly help the British tanks. Would probably push the Germans to uparmor sooner as well.

Crud, just not losing all that war materiel at Dunkirk would be a huge help to the UK.

And not having the French ports to sally from would greatly reduce the U-boat threat, which makes getting US lend-lease a lot easier.

But back to the ground. I suspect better ability to destroy German tanks would make the Africa campaign shorter, since it'd force Rommel to have fewer tanks available for his pushes.

Likewise, the Soviets getting Valentine tanks with 6pdrs instead of 2pds would possibly shorten the war on their side.

 

[Elan Vital]

On the ground side, the change to the 6pd as originally planned would greatly help the British tanks. Would probably push the Germans to uparmor sooner as well.

Crud, just not losing all that war materiel at Dunkirk would be a huge help to the UK.

And not having the French ports to sally from would greatly reduce the U-boat threat, which makes getting US lend-lease a lot easier.

But back to the ground. I suspect better ability to destroy German tanks would make the Africa campaign shorter, since it'd force Rommel to have fewer tanks available for his pushes.

Likewise, the Soviets getting Valentine tanks with 6pdrs instead of 2pds would possibly shorten the war on their side.

No such thing as an African campaign or Eastern front with mainland France in the fight. I have seen inconclusive info on the willingness of the Italians to exploit the distraction of the Entente by the Germans, but even then that front is as good as dead with French colonial forces and the Navy operational to assist the British. Sparing Rommel will be near impossible as well with a busy Franco-Belgian front.

Attacking the Soviets while the Entente is going strong is a similar deal.