WW2: When's the earliest the Allies could have plausibly lauched a successful invasion of France?

When the SYMBOL conference started the Joint Chiefs discussed for a few hours using the British 1st Army to seize Sardinia/Corsica in March 1943. I'm kind of intrigued by that one. Never mind whatever the Axis had in their Tunisia bridgehead. Those are either going to immediately evacuate, or be cut off as they were OTL.

In addition to placing the entirety of Italy in the range of 1943 Allied fighters, Corsica also allows domination of the Marsailles/Riveria port group.
 
Regarding a 1941 invasion, is there a limit to how late in the year that an invasion is feasible (weather, etc.)?

The Brits may decide on an invasion or large scale raid to help the Soviets (with things looking bad for the USSR) or to take advantage of Germany's attention being elsewhere. Oh, crazy idea that just popped into my head. A large scale raid into France to distract from planned operations in the Med and North Africa. There need to be PODs going back how far?

How far? I've turned up remarks about either Dill or Brooke secretly (they did not inform Churchill) discussing with French representatives the possibility of landings at Bourdeux & Bayonne to link up with Petains little army. These incidents are supposed to have occurred in the late summer or autumn with Dill, or in December in the case of Brooke. My take is the Greek disaster of the spring of 1941 did more than anything else to kill enthusiasm for a invasion in NW Europe. Dodge that and the Rommel experience in March-May 1941 and the Brits may be more confident.
 
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& now we are back around to a occasionally discussed alternate Mediterranean strategy. Not quite thread jacking, but definitely a digression.

Been ploughing through Barrs 'Eisenhowers Armies'. Am up to page 150 & am still in the background chapters about the preliminaries through 1941 to Ikes appointment as commander of Op TORCH. Theres a lot of random details for the state of British and US forces in 1941-42. Not enough to paint a complete picture, but useful. Whats really lacking are details of the German forces garrisoning France 1941-43. I have some partial items, but not remotely as much as with the US or Brits. A lot can be obtained by going through the the unit histories for the German army, & somewhat for the air and naval forces. But, that is slow and requires much double checking. It does appear the reserve for the Germans in the summer of 1941 were the field forces used in the Balkans campaign, which were neither committed to the opening of the BARBAROSA Op, or the occupation of the Balkans. A infantry corps of a couple divisions and a armored corps. Exactly how those were used in the east later that summer I've not yet followed up on, but they were available in July it appears. Of course other ground and air forces can be formed up for use vs a Brit invasion, but that gives the Red Army, or the Commonwealth in the Med a proportionate break.

In 1942 the rotation of spent formations from the east to the west for reviving was started. Some 'mobile' infantry divisions appeared in France, Belgium, & Germany. A couple burnt out armored divisions as well, plus the first SS armored divisions were formed in France & trained during the autumn and winter of 42. At this point Germany had started its 'long war' mobilization, but the results were not much apparent until 1943.
 
Regarding a 1941 invasion, is there a limit to how late in the year that an invasion is feasible (weather, etc.)?

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Depends on the coast. Moroccos Atlantic coast was successfully landed on in November 1942. Months earlier in 1942 the British staff group working up their version of SLEDGEHAMMER choose the Cotientin coast (later UTAH Beach) for a October landing, as its eastern facing sheltered it from the prevailing Atlantic storms.
 
...If HUSKY was meant to justify shipping in the Med, it's pretty clear it was an emotional rather than a logical argument. ...

When Brooke won his HUSKY vs ROUNDUP, or BRIMSTONE argument it was not clear the W Allies would so throughly dominate the air over the Med in just a few months. It looked more necessary from the perspective of January 1943 than in out hindsight. Perhaps had Eisenhower been less distracted through the remainder of January and February or March he might have successfully reversed the decision for HUSKY, but he was not getting much outside help in resolving the problems of SACMED. Mostly a lot of micromanaging memos from Churchill & others he could not ignore, plus the endless political struggles with the French.
 
When Brooke won his HUSKY vs ROUNDUP, or BRIMSTONE argument it was not clear the W Allies would so throughly dominate the air over the Med in just a few months. It looked more necessary from the perspective of January 1943 than in out hindsight. Perhaps had Eisenhower been less distracted through the remainder of January and February or March he might have successfully reversed the decision for HUSKY, but he was not getting much outside help in resolving the problems of SACMED. Mostly a lot of micromanaging memos from Churchill & others he could not ignore, plus the endless political struggles with the French.

The advantage of a TORCH which lands a group at Bone becomes more evident here. With Tunisia in Allied hands by the start of the new year, Allied air power over the Straits of Sicily takes on a new complexion.
 
I've never tried to assess the actual Axis threat to a Bone landing. Given the size of the port a full corps, like the Western TF may not have been practical. Maybe shift a portion of a reinforced Eastern TF to Bone?
 
Marshal & King who thought the NW Europe invasion was a done deal were prepared to discuss the details like supreme commander, or ramping Op BOLERO back up, were wholly unprepared for Brookes seeming Volte-Face on the planned strategy.

Not convinced about this - Bolero being ramped back up was a prerequisite for Roundup, but as far as I can recall from Rupenthal that was not being considered on the US side.
 
I'm unsure what "considered" would be in this context. BOLEROwas reduced to make way for Op TORCH & its follow up. When the SYMBOL meeting convened the African campaigns termination was still a open question. While everyone suspected the prospects were not good a detailed report and estimate from Eisenhower did not come until the conference was underway. Beyond that the estimates, requirements, and plans for BOLERO were on the table & the information available to update them. Returning the BOLERO movement to the original intent, and the other preparations gives four to six months of preparation time from January 1943 to the projected invasion. Op HUSKY had between five & six months prep, the combined BAYTOWN AVALANCHE Ops maybe four months, the original ANVIL operation had four months to prepare.

In any case its difficult to dismiss the conclusions of several historians separately commenting on the expectations Marshal brought to Casablanca.
 
I'm unsure what "considered" would be in this context. BOLEROwas reduced to make way for Op TORCH & its follow up.

I'll have to dig back into Rupenthal, but the US did not actually tell the UK that Bolero was being scaled back in the autumn of 1942, and Bolero's focus shifted to air forces rather than ground forces.

The problem with scaling Bolero up again for a 1943 invasion post the Casablanca conference is that the arrival rate for US divisions is too low at 1 (possibly 2) a month, given that a reasonable expectation is that a US Army Group will be needed in the first month or so after the invasion.
 
I'll have to dig back into Rupenthal, but the US did not actually tell the UK that Bolero was being scaled back in the autumn of 1942, and Bolero's focus shifted to air forces rather than ground forces.

I need to review Ruppenthal again too.

Its difficult to think the Brits were standing on the Liverpool docks wondering where all those Yank infantry were, who they were expecting. The US Army never gave them even outline shipping schedules for the BOLERO op?

The problem with scaling Bolero up again for a 1943 invasion post the Casablanca conference is that the arrival rate for US divisions is too low at 1 (possibly 2) a month, given that a reasonable expectation is that a US Army Group will be needed in the first month or so after the invasion.

Are you sure? I don't remember a US Army group being required in the first 30 days of Op OVERLORD. As in the previous discussions there is the question of adding in cargo shipping saved elsewhere given the priority of this operation over other. ie: Marshal not buying off on the S Pacific offensives. Less material for China, reducing shipments to the USSR 10 or 15 %. Postphoning Mediterranean operations. The savings in cargo capacity add up. The provision is not 1-1. A single cargo ship scheduled for the 90 day round trip to Australia or the Solomons can be scheduled for three 30 day roundtrips to the UK or French ports.
 
Are you sure? I don't remember a US Army group being required in the first 30 days of Op OVERLORD.

14 divisions is a bit heavyweight for an Army.

https://www.loc.gov/resource/g5701s.ict21031/?r=0.055,0.128,1.019,0.643,0

I think we only disagree on nuances. My major complaint is with historians repeating unthinkingly "Marshall said that Torch diverted resources to the Mediterranean, and this prevented a 1943 invasion" without checking whether this is a fair representation of events.

EDIT: Ruppenthal Vol 1, p99 onwards covers what happened to Bolero eg Bolero Key Plan 3rd Edition published 11 Nov 1942 was on the basis of a balanced force including 5 divisions to be received by May 1943 (although this never happened); a shipping study at about the same time said equivalent of 2 divisions could be sent to the UK by mid-April (to add to the existing total of 1).

At Casablanca it was estimated that 15 to 19 divisions could be sent to the UK by the end of 1943, but heavily weighted into the second half.
 
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Agree there. There are a large number of unknowns we have barely touched on in those discussions. Theres a few, like the 1943 attrition rate of Axis air forces that are fairly clear, but some like the actual cargo delivery options that seem beyond reach.

How much did diversion of escorts to the supply effort to NW Africa affect the battle in the North Atlantic December-March 1943?

Were the 4000+ Allied aircraft sent to NW Africa best used there, or would they have been more destructive elsewhere?

How many US ground units were ready?

How would the attrition rates/destruction of ground and air forces in the is hypothetical front differ from the historical campaigns.

How do the battles of 1944 differ with the US Army having 20-30+ veteran divisions in Europe vs the 6-7 of OTL?

14 divisions is a bit heavyweight for an Army. ...

At a rate of 1.5 arriving per month thats six by 1 May or nine on 1 Aug, plus the two already in Ireland and Iceland in December 1942. Not as large a crowd, but then the Germans have less as well.
 
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