No more fighting the last war - France keeps a strategic reserve in 1940

Yes, they had some reserves even OTL, and part of them were committed to Stonne and other places, some of them got chewed up by the advancing German panzer formations etc. etc.

This is not about that. This is about not implementing the 'Breda variant' to the OTL 'Dyle Plan', meaning that the 7th Army (one of France's best formations), remains part of the strategic reserve and is kept in place north of Reims, a stone's throw away from Sedan. This would put them in an excellent position to be deployed against the German Schwerpunkt when they try to cross the Meuse and consolidate their bridgehead.

Given the French command structure, they are liable to screw it up anyway by dithering for too long. Would they though? Or do they have a chance to make this work?
 
But that's different - it assumes for some strange reason that the French don't actually advance into Belgium at all and just sit idly at the border
Err... no, it assumes that the Dyle plan is never adopted and instead the preceding plan (the Escaut plan) remains - this still has them holding on to a sizeable chunk of Belgium. Georges and Gamelin had a major disagreement about adopting the Dyle plan in the first place, with Gamelin feeling that it committed too much of their mobile forces deep into Belgium, and indeed he specifically questioned what would happen if the Germans attacked through the Ardennes if the plan was adopted!

I'm not convinced that just getting rid of the Breda Variant and sticking to the Dyle plan would make much of a difference - you've got rid of the forces with the furthest to go, but you're still committing major forces to a movement deep into Belgium and which only protects a part of the country. The only significant saving in mechanised forces comes from falling back to the Escaut plan and accepting that you're going to have to fight your way back across large parts of Belgium when you're ready for it (something nobody from that generation of Frenchman really wanted to do).

It should also be noted that in A Blunted Sickle I also gave the French a lot of luck in dealing with the German attack - in essence I put some of their better generals (Prioux and Alanbrooke) in the right place at the right time and gave them orders to form a blocking position in front of the Germans: orders which of course arrived three days too late and had them instead hit the German flanks. About as much luck as I'd say the Germans had in OTL, so unlikely but plausible. The Germans were running a massive gamble in 1940 however - once that went wrong for them the war is essentially over. Still, keeping France going through 1940 is not easy at all.

StrategicMap-HistoricalAlliedPlan.jpg
 
Looking at that map, doesn't the Dyle plan mean only covering about half as much front? Which would make it not quite as daft as it seems...
 
Looking at that map, doesn't the Dyle plan mean only covering about half as much front? Which would make it not quite as daft as it seems...
Probably a bit less than half - my best guess would be two-thirds. Gamelin wouldn't have got to command the French Army if he was a complete moron, and we're looking at the plan with almost 70 years of hindsight. The Breda variant is a bit worse, only really matching the length of front of the Escaut plan, but it promised to keep the Dutch in the war if it worked.

The real issue with the plan is that it shifts the whole Centre of Gravity of the French effort to the left - if they'd adopted the Escaut plan then most of the French forces could have stood still and they could have left the BEF to do most of the advancing into Belgium, with a far more formidable river line to hide behind when they got there. Worse, the Gembloux Gap in the centre has no natural obstacles and is poorly defended - meaning that they had to commit the Cavalry Corps to it and with it their best mobile troops. The effect wasn't really on the number of reserves they had - if anything the Dyle plan left them with a bigger reserve - but the fact that it committed their best and most mobile troops and so cut down the quality of what they had in reserve. That meant when they did commit their reserves, it wasn't their best equipped or most mobile troops and they weren't led by their best and most aggressive officers - who were off fighting (and winning) a battle in Belgium instead.

The attraction of this as a POD for me is that it came so close to actually happening. To quote from To Lose A Battle (Horne):
On 24th October, Gamelin issued orders to the armies of the North-East front, telling them to be ready to advance to a defensive position along the Escaut (or Scheldt) river, running from Antwerp to Ghent. In terms of distance of approach march, the 'Escaut Plan' represented the most prudent of the Low Countries options open to the Allies. But it was an awkwardly long line to hold, and at the same time it covered so small a portion of Belgian territory that Brussels would be abandoned and the bulk of the Belgian Army simply left, un-supported, to its fate. General Georges, however, immediately registered the strongest misgivings about any 'deeper progression into Belgium'. The Army was still not sufficiently ready to risk being caught by a German offensive in unprepared positions, far from its bases. Despite Georges doubts, on 15 November Gamelin gave out his amended Instruction No.8, in which the Allied forces were to move up to the Dyle Line, stretching from Antwerp in the south to above Dinant on the Meuse. The Dyle itself was little more than a wide stream, and it involved the French Army going still further out on the Belgian limb. Once again, General Georges expressed his reservations. On the credit side of the original 'Dyle Plan', it constituted a shorter line, it protected Brussels and gave a better chance of linking up with the Belgian defenders in their Albert Canal positions, and it committed no more than ten French divisions. Gamelin himself, however, was not satisfied; it made no provision for lending a hand to the Dutch in case of attack.

Towards the end of November, Gamelin requested General Billotte, commander of No.1 Army Group, to study an extension of the Dyle plan northwards from Antwerp in the direction of Breda, which lay twice as far from the French frontier as from Germany. On hearing of this new inflationary development of Gamelin's Belgian strategy, Georges objected vigorously. In the margin of Billotte's report, he wrote: 'This is of the order of an adventure... Don't let's engage our effectives in this affair', and on 5 December he sent it to Gamelin with an accompanying memorandum which contained this highly pertinent and prescient warning:

The problem is dominated by the question of available forces... There is no doubt that our offensive manoeuvre in Belgium and Holland should be conducted with the caution of not allowing ourselves to commit the major part of our reserves in this part of the theatre, in face of a German action which could be nothing more than a diversion. For example, in the event of an attack in force breaking out in the centre, on our front between the Meuse and the Moselle, we could be deprived of the necessary means for a counter-attack...

Now I'm not too sure how much credibility to give to Georges' comments given that his relations with Gamelin were somewhere between bad and poisonous (yet another thing the French Army got wrong!), but he isn't going to invent things like that. There was clearly a concern on his part that the French army was too heavily committed to Belgium and that it would damage their ability to respond to an attack elsewhere - an attack which ultimately happened and which the French proved unable to counter.
It should be remembered that until the adoption of the Manstein plan then the Dyle-Breda plan was actually a really good one - it offered the best chance of rescuing the 700,000 men of the Belgian army and ensuring that the fighting was on Belgian rather than French soil. The weakness was the one that Georges identified - the total road march to position was much longer than that for the Escaut plan, and there were no natural obstacles to hold on arrival much bigger than an oversized stream:
the_river_dyle__by_bermiro-d77jpu3.jpg

The decision was really one between a plan that committed you to fighting a much longer and more costly war but which had less of a risk of going badly wrong, and one that promised to save a lot of blood and treasure but which wasn't as robust against the Germans pulling a rabbit out of the hat. Gamelin's judgement was that a rabbit was really unlikely (and in this he was supported by just about everyone) - unfortunately for the French he was wrong, and Manstein pulled off a miracle.
 
So, back to the OP's question. If some of their Best mobile forces are held in reserve in a modified Dyle plan, what happens then?
Gembloux gap and Sedan?
What happens if they Lose at Gembloux gap and win/hold off for a while at Sedan?
 
So, back to the OP's question. If some of their Best mobile forces are held in reserve in a modified Dyle plan, what happens then?
Gembloux gap and Sedan?
What happens if they Lose at Gembloux gap and win/hold off for a while at Sedan?
Even a draw at Sedan is disastrous for the Germans. The big thing they had going for them throughout the campaign was that they could move faster than the French could react. If they stop moving even for a couple of days, the French find their feet again and everything starts working again. Then the Germans have to really fight their way through, rather than just running rings around the French. That means at least an order of magnitude more casualties for the Germans, and probably a campaign that stretches on into 1941. If it does, the Germans have lost the war.

Gembloux is important for holding the Dyle plan together - if they fail to hold it then there really aren't any obstacles before the field fortifications on the French border. Still, if the Cavalry Corps isn't at Gembloux that probably means that the French haven't sent much there - Hannut (precursor to Gembloux) was fought from the morning of the 12th of May and the German attack only started on the 10th with Prioux arriving on the 11th. The Cavalry Corps was only of a pretty small number of fully motorised units in the French army with organic tank support - so one of the few units able to get there in time with the forces to fight a battle and hope to win.

What probably happens if the Cavalry Corps is placed in reserve and ends up being sent to Sedan is that the Germans get to Gembloux before the French and there is some sort of engagement south-west of there on the 13th. At this point a sizeable fraction of the French army haven't got very far from their prepared positions on the French border, so planned or not we probably end up with something close to the Escaut plan because if you're committing the most mobile troops to the reserve they probably can't implement the Dyle plan before the Panzers get there. Importantly though it isn't the main strength of the German army or anywhere close to it - that's coming up through the Ardennes. Overall the fighting between the French and Germans in Belgium was pretty even - they were forced back as much through lack of supplies as through German victories. That's the major point about winning at Gembloux - it gets them a big hole in the Dyle line, but the French really aren't on the Dyle line yet anyway. The German forces coming up through Belgium really aren't big enough to destroy the French armies on their own, they can push them back and inflict significant losses at best but the only way to land a killer blow is the troops coming through Sedan.

Remember, it was planned on the Germans being held up for some time at the Albert Canal line followed by an orderly retreat of the Belgian army to the French lines, behind which they could rest and refit - hence the critical importance of protecting Brussels. In reality the German Fallschirmjägers broke the Albert Canal line on the morning of the 10th of May with the defanging of Eben Emael and the capture of the bridges over the canal. Once that happens all the plans are out of the window and it's scrambling to save what you can - the Panzers are going to be there a lot earlier than expected.
 
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