How "should" WWII in 1940 have gone?

[Jacarí]

No I would not choose to do what they did 'without hindsight' as they were the plans of lunatics - which is partially why they succeeded - but so much could have gone wrong!

Well as for the German fleet being wrecked - the KM lost 10 fleet destroyers (of 20), 1 Heavy Cruiser (of 2) , 2 light cruisers (of 6) and 6 Submarines and 21 transport representing 10% of its then total transport fleet tonnage.

A further 2 'torpedo boats' (light destroyers) and 15 smaller warships were also sunk

Of the remaining surface fleet at the end of the campaign only 3 Crusiers and 4 fleet destroyers were operational - the rest of the ships damaged including both Battleships and the other 2 cruisers as well as the other remaining destroyers sustained damage during the campaign.

If that is not being wrecked then I am not sure what is?

1 CA of 5, have to count the reclassified Deutschlands.

No BBs lost.

The only proportionally significant losses were the DDs.

Damaged ships get repaired.

And all that was suffered in teh context of a major and highly unlikely strategic victory.

It was cheap.

The RN had crap to show for their losses but shame.

 

[Jacarí]

The "long, unprotected flank" was not suicidal. The initial reckless push westwards was done in full knowledge of the French sluggishness, and it yielded significant dividends in the effective destruction of two of four French tank divisions in the area, after which they actually paused for a few days and let the foot infantry deploy into the salient to defend the flank before they resumed their advance to the channel. When they reached the channel, the salient's left flank was well-protected. The French would have had considerable difficulty breaking through that "long, unprotected flank." And the Luftwaffe was well-positioned to parry any French counterattacks by forcing them to disperse en route, which is exactly what happened when the French tried to deploy their armored reserves during Case Red. Just because Case Yellow was the best plan available to the Germans, doesn't mean it was just a hail mary.

The worst thing you can do in war is underestimate the enemy, the Germans didnt, no one expected it to work, many opposed it, the ones that supported it did so because they knew that if they didnt win outright, they would just lose later.

The German infantry was 2 days behind the tanks at some point, that is a wide open flank, which is why OKH was frantically trying to stop the PzDiv again and again, they could see the map.

 

[RedSword12]

The worst thing you can do in war is underestimate the enemy, the Germans didnt, no one expected it to work, many opposed it, the ones that supported it did so because they knew that if they didnt win outright, they would just lose later.

The German infantry was 2 days behind the tanks at some point, that is a wide open flank, which is why OKH was frantically trying to stop the PzDiv again and again, they could see the map.

At any given point in the battle, the French were further behind the German panzers than the infantry, whether in responsiveness or by physical distance. If you look at the unit deployments, the German salient was not as vulnerable as people claim; the panzers paused for a few days to let infantry catch up, and when they rushed for the channel, they delegated a substantial portion of their best units to defending the west flank, which the French were not yet in position to threaten even if they wanted to, because they were still playing catch-up. The most vulnerable point in Fall Gelb was when the Germans had just crossed the Meuse, and the French failed to exploit that vulnerability not because of any one specific decision that can easily be defeated by POD, but because of deep systemic problems in their military which can't just be handwaved away.

 

[tomo pauk]

True, the Germans were better, no doubt about that... but they took a huge risk, one that shouldnt have worked... like in Norway... or Poland... but in war everything is relative.

For the Germans (as well as for the others), they indeed needed not to be the best, but to be sufficiently better that their opponents. That they were many times during the 1st two years of ww2.
War is always a risk, Germans had no problems taking that risk.

FUnny enough Barbarossa was, on paper, the less risky offensive they undertook.

On paper and in reality, Germans were not aware of how much the logistics matter once the requirement was that armies should march 300-400-500 km. That mattered little if the enemy can be defeated within these geographic boundaries, like it was the case with Poland or France, let alone with Belgium or Denmark.
300-400-500 km was chump change for anyone commanding from Moscow.

Poland was an offensive by a green army that had a skeleton garrison and a lot of propaganda protecting its back.

Polish army was even more green, with far less aircraft, infantry and tanks, and with worse aircraft and tanks. French and British didn't give any impression that they are willing to invade Germany big time, so Germans simply took the opportunity when it arose.

France was a land offensive against an enemy superior in every numerical metric, one executed on a suicidal fashion that could cost you the war.

Luftwaffe was more numerous force by a large margin, with both fighters and bombers being better, and with doctrine that favored combined arms (ie. go in and when needed support the Army) and initiative. Germans fielded perhaps ten anti-aircraft guns for each AA gun the French fielded, and their AA guns were better. Numerical metric will be ill able to describe the experience the Germans gained before 1940.
I'm not sure that anyone was expecting that main French defensive investment - the Maginot line - will be able to move itself in Belgium, let alone in the Netherlands. Certainly Germans didn't expected that to happen, so they planned accordingly. Expecting that French navy takes part in the future short war was also unrealistic.

 

[Jacarí]

For the Germans (as well as for the others), they indeed needed not to be the best, but to be sufficiently better that their opponents. That they were many times during the 1st two years of ww2.
War is always a risk, Germans had no problems taking that risk.

Well, its more like they literally had no choice, they either win quickly or lose.

On paper and in reality, Germans were not aware of how much the logistics matter once the requirement was that armies should march 300-400-500 km. That mattered little if the enemy can be defeated within these geographic boundaries, like it was the case with Poland or France, let alone with Belgium or Denmark.
300-400-500 km was chump change for anyone commanding from Moscow.

I recall they were quite aware of the fact, that they only swept that under the rug fully expecting the Soviets to fold way before distance became an issue. Not an unreasonabl expectation, but an ultimately wrong one.

Polish army was even more green, with far less aircraft, infantry and tanks, and with worse aircraft and tanks. French and British didn't give any impression that they are willing to invade Germany big time, so Germans simply took the opportunity when it arose.

Sure, but I dont think it was reasonable to expect the wallies to just sit there... like they did.

Luftwaffe was more numerous force by a large margin, with both fighters and bombers being better, and with doctrine that favored combined arms (ie. go in and when needed support the Army) and initiative. Germans fielded perhaps ten anti-aircraft guns for each AA gun the French fielded, and their AA guns were better. Numerical metric will be ill able to describe the experience the Germans gained before 1940.
I'm not sure that anyone was expecting that main French defensive investment - the Maginot line - will be able to move itself in Belgium, let alone in the Netherlands. Certainly Germans didn't expected that to happen, so they planned accordingly. Expecting that French navy takes part in the future short war was also unrealistic.

Yes, they had a qualitative advantage, specially i the air, but the OKW had serious doubts about its own plan, they were undertaking an offensive with little prospects of success. The French moved successfully onto the Dyle, that part worked, only failures elsewhere dislodged them from there. It was not a bad idea, and it wasimplemented reasonably well.

The failure was elsewhere, and it was mainly in their doctrine.

 

[Jacarí]

At any given point in the battle, the French were further behind the German panzers than the infantry, whether in responsiveness or by physical distance. If you look at the unit deployments, the German salient was not as vulnerable as people claim; the panzers paused for a few days to let infantry catch up, and when they rushed for the channel, they delegated a substantial portion of their best units to defending the west flank, which the French were not yet in position to threaten even if they wanted to, because they were still playing catch-up. The most vulnerable point in Fall Gelb was when the Germans had just crossed the Meuse, and the French failed to exploit that vulnerability not because of any one specific decision that can easily be defeated by POD, but because of deep systemic problems in their military which can't just be handwaved away.

Yes, the French were slow, much to slow and that meant they werent there when the opportunities did present themselves, the Germans WERE overextended and vulnerable... but there were no French troops there to take advantage of the gaps... and that was my point, with a slightly better response, the French should have been able to cutoff the Germans.

But they werent there, their doctrine stressed communication security rather than speed, so everything was slow while the Germans made everything by radio. Still, there were mistakes that had nothing to do with comms, personal failures that cost them dearly and facilitated the German breakthrough.

 

[tomo pauk]

Well, its more like they literally had no choice, they either win quickly or lose.

They have had the choice - win fast. That they did.
Choosing the other potion was a worse choice.

Sure, but I dont think it was reasonable to expect the wallies to just sit there... like they did.

There were no Allies worth speaking about to pounce against Germany in September of 1939 - it was just France - and they 'telegraphed' their intentions the moment the 1st tons of concrete were poured into the Maginot line. The intentions being to sit behind their fortifications and hope that Germany doe that things as per French plan.

Yes, they had a qualitative advantage, specially i the air, but the OKW had serious doubts about its own plan, they were undertaking an offensive with little prospects of success.

Advantage was also qualitative: in machines, training, doctrine and experience. Every offensive campaign will had it's doubters, even Ike was counting with possibility that Overlord is defeated and thrown into Channel, despite all the preparations and Germans receiving a hefty beating before June 1944.

The French moved successfully onto the Dyle, that part worked, only failures elsewhere dislodged them from there. It was not a bad idea, and it wasimplemented reasonably well.
The failure was elsewhere, and it was mainly in their doctrine.

I have no intentions to congratulate the French on moving, as if that was some achievement. It was fighting that mattered, there was no medals for second place there.

 

[Jacarí]

They have had the choice - win fast. That they did.
Choosing the other potion was a worse choice.

Was it a choice? They were certain, and rightfully so, that they would lose a long war, they either throw everything into winning quickly or just wait for the inevitable collapse.

There were no Allies worth speaking about to pounce against Germany in September of 1939 - it was just France - and they 'telegraphed' their intentions the moment the 1st tons of concrete were poured into the Maginot line. The intentions being to sit behind their fortifications and hope that Germany doe that things as per French plan.

Sure, it was the French army... but the RAF taking a more active role was a possibility... only they didnt. And the fact the Maginot line existed didnt meant they would just sit there when they could have just marched into the Ruhr, that is one hell of an assumption adn gamble.

Advantage was also qualitative: in machines, training, doctrine and experience. Every offensive campaign will had it's doubters, even Ike was counting with possibility that Overlord is defeated and thrown into Channel, despite all the preparations and Germans receiving a hefty beating before June 1944.

One thing is to consider and have a plan B... another thing is what the Germans thougth about Case Yellow itself specifically, they had no confidence on that plan at all. German plans were gamble, after gamble, after gamble because they had no choice, either win big and fast or lose.

I have no intentions to congratulate the French on moving, as if that was some achievement. It was fighting that mattered, there was no medals for second place there.

The French did fight well in Belgium, but their second rate troops were... really second rate.

 

[Carl Schwamberger]

The "long, unprotected flank" was not suicidal. The initial reckless push westwards was done in full knowledge of the French sluggishness,

There evidence there was no full knowledge. Halder had the various plans gamed out, in both map and field exercises through the autumn of 1939, and winter of 1940. In all these exercises the Germans failed to gain decisive results. Some of the plans failed miserably, some succeeded tactically but fail strategically. In all cases the enemy reaction was judged to be executed at a competent speed similar to the German speed in execution. Mays in 'Strange Victory'* notes one exception. At a OKW sponsored map exercise in March 1940 the Lt Col running the French or Allied forces disagreed with the idea the French would react with decisive speed to the German advance. He slowed the French reaction cycle by a day. The results of the exercise were more favorable to the attacker. Post exercise this delay of Allied reaction was criticized as "unrealistic" by other participants.

After the campaign a lot of participants claimed they'd been behind it all along & post war a lot of pure BS was written. No different than in any other army.

During the winter long work up to the offensive Most of the Generals were skeptical. Kliest & Guderian were two of the few exceptions. Most of the Army commanders expected French counter attacks to cut off and isolate Kliests Panzer Group as it ran out ahead beyond the support of the following infantry corps. Halder & Rundsteadt were ambivalent, but Halder ran with it because every other plan tested had been worse. Hitlers memos to Halder, and the minutes of meetings at OKW show Hitler was not a strong supporter of the Sickle Cut plan. At some points he did prefer it, other days he argued for others. He was actually all over the place switching support from one conference top the next. He seems to have been increasingly agitated by the failures of the field exercises and map game to reach the goals necessary for a strategic victory. Like most of his generals he thought the French would crush the exposed Panzer Group.

This is bourne out by his behavior during the campaign. On the 12th May he asked holder if the armored group should not wait at the Maas River, for the infantry corps to catch up. Two days later he again questions Halder more forcefully about not advancing further from the bridgeheads and again waiting on the infantry. This last was barely sixteen hours after he had been mainly happy about the success of the river crossing. On the 16th he demanded Halder give a order to halt the armored group again. This was the incident where holder sent a order to halt for 24 hours, but included permission to continue a 'reconnaissance in force'. On the 18th Hitler again demanded a halt arguing as before the French were about to crash the flanks of the armored group. Halder talked him down of the ceiling and was able to cancel the order the next day, and the panzer corps and division commander had continued to probe ahead anyway.

It is correct Kliest and Guderian were hopeful. Guardedly confident as it were when the campaign started. But, the majority of the corps and army commanders thought they had seen the last of the panzerwaffe when it plunged off into Belgium 10th May.

*Mays 'Strange Victory' is a study of the evolution fo the Sickle Cut plan from its first embryonic appearance in November 1939 though the finishing touches in March/April 1940. May relied primarily on the records of OKW, and other written records of those months. He does refer to the post war writing of the various participants but often notes the inconsistancies and contradictions in those. ie: Post war Guderian claimed he met with Manstein when he was writing the plans for the November map exercise at OKW HQ Zossen Germany. Manstein asked for assistance in understanding how tanks should be used, since all his training was in infantry. Post war Mansterin denied he ever met with Guderian, and received no guidance from him.

 

[RedSword12]

There evidence there was no full knowledge. Halder had the various plans gamed out, in both map and field exercises through the autumn of 1939, and winter of 1940. In all these exercises the Germans failed to gain decisive results. Some of the plans failed miserably, some succeeded tactically but fail strategically. In all cases the enemy reaction was judged to be executed at a competent speed similar to the German speed in execution. Mays in 'Strange Victory'* notes one exception. At a OKW sponsored map exercise in March 1940 the Lt Col running the French or Allied forces disagreed with the idea the French would react with decisive speed to the German advance. He slowed the French reaction cycle by a day. The results of the exercise were more favorable to the attacker. Post exercise this delay of Allied reaction was criticized as "unrealistic" by other participants.

After the campaign a lot of participants claimed they'd been behind it all along & post war a lot of pure BS was written. No different than in any other army.

During the winter long work up to the offensive Most of the Generals were skeptical. Kliest & Guderian were two of the few exceptions. Most of the Army commanders expected French counter attacks to cut off and isolate Kliests Panzer Group as it ran out ahead beyond the support of the following infantry corps. Halder & Rundsteadt were ambivalent, but Halder ran with it because every other plan tested had been worse. Hitlers memos to Halder, and the minutes of meetings at OKW show Hitler was not a strong supporter of the Sickle Cut plan. At some points he did prefer it, other days he argued for others. He was actually all over the place switching support from one conference top the next. He seems to have been increasingly agitated by the failures of the field exercises and map game to reach the goals necessary for a strategic victory. Like most of his generals he thought the French would crush the exposed Panzer Group.

This is bourne out by his behavior during the campaign. On the 12th May he asked holder if the armored group should not wait at the Maas River, for the infantry corps to catch up. Two days later he again questions Halder more forcefully about not advancing further from the bridgeheads and again waiting on the infantry. This last was barely sixteen hours after he had been mainly happy about the success of the river crossing. On the 16th he demanded Halder give a order to halt the armored group again. This was the incident where holder sent a order to halt for 24 hours, but included permission to continue a 'reconnaissance in force'. On the 18th Hitler again demanded a halt arguing as before the French were about to crash the flanks of the armored group. Halder talked him down of the ceiling and was able to cancel the order the next day, and the panzer corps and division commander had continued to probe ahead anyway.

It is correct Kliest and Guderian were hopeful. Guardedly confident as it were when the campaign started. But, the majority of the corps and army commanders thought they had seen the last of the panzerwaffe when it plunged off into Belgium 10th May.

*Mays 'Strange Victory' is a study of the evolution fo the Sickle Cut plan from its first embryonic appearance in November 1939 though the finishing touches in March/April 1940. May relied primarily on the records of OKW, and other written records of those months. He does refer to the post war writing of the various participants but often notes the inconsistancies and contradictions in those. ie: Post war Guderian claimed he met with Manstein when he was writing the plans for the November map exercise at OKW HQ Zossen Germany. Manstein asked for assistance in understanding how tanks should be used, since all his training was in infantry. Post war Mansterin denied he ever met with Guderian, and received no guidance from him.

I'm referring to specifically the time when Guderian rushed west right after crossing the Meuse. The lack of a rapid French counterattack evidenced that the French were in a state of disarray (which they were), so it was reasonable to believe that taking such a risk would be more advantageous than waiting for the French to put together a defense.

 

[MxCokoko]

I think to prevent the fall of France you need two things:
- The French to create a cohesive defensive line further south than OTL, maybe as a result of ITL fears that Belgium would capitulate much faster due to the German blitzkrieg of Poland. This would probably stretch the line, but as long as there's enough to buy time for reinforcements to stop (and potentially counter-attack) the Ardennes Blitzkrieg force, this could be a wildly successful thing. Not sure how exactly it'd go, but my next point might come into play.
- The B.E.F. moves further south (somewhere near the Franco-Belgian border) similar to the first point and is more able to react to German attacks on Belgian and French forces.

 

[Cryhavoc101]

1 CA of 5, have to count the reclassified Deutschlands.

No BBs lost.

The only proportionally significant losses were the DDs.

Damaged ships get repaired.

And all that was suffered in teh context of a major and highly unlikely strategic victory.

It was cheap.

The RN had crap to show for their losses but shame.

Well that's an opinion I guess

 

[Ambusher11]

FUnny enough Barbarossa was, on paper, the less risky offensive they undertook.

If Stalin had committed suicide after the fall of Minsk and Barbarossa succeeded due to the Soviet government collapsing, I'd bet that the Soviet Union would probably be viewed as being less likely to have stood a chance of successfully fighting against the Nazis than France did.

 

[Carl Schwamberger]

I'm referring to specifically the time when Guderian rushed west right after crossing the Meuse. The lack of a rapid French counterattack evidenced that the French were in a state of disarray (which they were), so it was reasonable to believe that taking such a risk would be more advantageous than waiting for the French to put together a defense.

Yep, Guderian on the spot saw aggressive action was better than waiting for developments. The conversations between him & Kliest that week are fascinating when you understand the context and the other sequence of events on both sides in the 19th Corps area of operations. Perhaps the most fascinating is the conversation between the two about which direction to go. To Paris? Or to the Channel? That had been debated and tested in the map exercises. There was a lot of complicated consideration for one of the other, but based on weak intel and information about events further north Kliest guessed they should head for the Channel. I don't know if he had earlier conversations with Rundsteadt or Halder on that question, but Guderians perspective is the decision for Paris was still possible on the 14th.

In the French 20th Corps Flavigny had some of the better elements of the French army. had acted aggressively on the 14th and attacked in the late afternoon as was possible Guderian would have had his hands full defending his flank for some 48 hours or more. Instead Flavigny dithered, postponed, and then canceled, ordering his corps to disperse into defensive positions. This in direct disobedience to Huntzingers order to attack on the 14th to Sedan as aggressively as possible.

 

[Giant Man Eating Rabbits]

... but the RAF taking a more active role was a possibility... only they didnt.

I'm pretty sure all the dead aircrew from the Battles, Blenheim's and Wellingtons would care to differ!

 

[Band in China]

There evidence there was no full knowledge. Halder had the various plans gamed out, in both map and field exercises through the autumn of 1939, and winter of 1940. In all these exercises the Germans failed to gain decisive results. Some of the plans failed miserably, some succeeded tactically but fail strategically. In all cases the enemy reaction was judged to be executed at a competent speed similar to the German speed in execution. Mays in 'Strange Victory'* notes one exception. At a OKW sponsored map exercise in March 1940 the Lt Col running the French or Allied forces disagreed with the idea the French would react with decisive speed to the German advance. He slowed the French reaction cycle by a day. The results of the exercise were more favorable to the attacker. Post exercise this delay of Allied reaction was criticized as "unrealistic" by other participants.

After the campaign a lot of participants claimed they'd been behind it all along & post war a lot of pure BS was written. No different than in any other army.

During the winter long work up to the offensive Most of the Generals were skeptical. Kliest & Guderian were two of the few exceptions. Most of the Army commanders expected French counter attacks to cut off and isolate Kliests Panzer Group as it ran out ahead beyond the support of the following infantry corps. Halder & Rundsteadt were ambivalent, but Halder ran with it because every other plan tested had been worse. Hitlers memos to Halder, and the minutes of meetings at OKW show Hitler was not a strong supporter of the Sickle Cut plan. At some points he did prefer it, other days he argued for others. He was actually all over the place switching support from one conference top the next. He seems to have been increasingly agitated by the failures of the field exercises and map game to reach the goals necessary for a strategic victory. Like most of his generals he thought the French would crush the exposed Panzer Group.

This is bourne out by his behavior during the campaign. On the 12th May he asked holder if the armored group should not wait at the Maas River, for the infantry corps to catch up. Two days later he again questions Halder more forcefully about not advancing further from the bridgeheads and again waiting on the infantry. This last was barely sixteen hours after he had been mainly happy about the success of the river crossing. On the 16th he demanded Halder give a order to halt the armored group again. This was the incident where holder sent a order to halt for 24 hours, but included permission to continue a 'reconnaissance in force'. On the 18th Hitler again demanded a halt arguing as before the French were about to crash the flanks of the armored group. Halder talked him down of the ceiling and was able to cancel the order the next day, and the panzer corps and division commander had continued to probe ahead anyway.

It is correct Kliest and Guderian were hopeful. Guardedly confident as it were when the campaign started. But, the majority of the corps and army commanders thought they had seen the last of the panzerwaffe when it plunged off into Belgium 10th May.

*Mays 'Strange Victory' is a study of the evolution fo the Sickle Cut plan from its first embryonic appearance in November 1939 though the finishing touches in March/April 1940. May relied primarily on the records of OKW, and other written records of those months. He does refer to the post war writing of the various participants but often notes the inconsistancies and contradictions in those. ie: Post war Guderian claimed he met with Manstein when he was writing the plans for the November map exercise at OKW HQ Zossen Germany. Manstein asked for assistance in understanding how tanks should be used, since all his training was in infantry. Post war Mansterin denied he ever met with Guderian, and received no guidance from him.

This looks like gold, where can I read about it?

 

[Jacarí]

I'm pretty sure all the dead aircrew from the Battles, Blenheim's and Wellingtons would care to differ!

The RAF committed a small part of its force, I am pretty sure the French didnt appreciate that when they were being swarmed by German planes.

 

[RedSword12]

This looks like gold, where can I read about it?

It's in Strange Victory, which is a book about the 1940 campaign.

 

[CaptainCalvert]

I think to prevent the fall of France you need two things:
- The French to create a cohesive defensive line further south than OTL, maybe as a result of ITL fears that Belgium would capitulate much faster due to the German blitzkrieg of Poland. This would probably stretch the line, but as long as there's enough to buy time for reinforcements to stop (and potentially counter-attack) the Ardennes Blitzkrieg force, this could be a wildly successful thing. Not sure how exactly it'd go, but my next point might come into play.
- The B.E.F. moves further south (somewhere near the Franco-Belgian border) similar to the first point and is more able to react to German attacks on Belgian and French forces.

Political pressures meant that the BEF couldn't be used as a strategic reserve, where its mobility could have been useful, and had to be seen to be in the front line. In principle, defending Dyle or Eschaut line would have allowed for a reserve, although the best troops (the DLMs) were used in the Dyle plan's advances
However, once Gamelin had decided to do away with a strategic reserve and go for the Breda plan, the whole defence plan became vulnerable, and it's hard to see things going much better while he is still in charge.
Having said that, imagine what a genius he would look like if Sedan had been held or repulsed, and the Dutch and Belgian defences had (just) held.

 

[Derwent Water]

Another gem from "Strange Victory" was the authors discussion about what would have happened had the French issued an ultimatum to the Belgian Government in the Autumn of 1939, bacicly you join us now and we will move to protect your Easten frontier over the winter, or you will not be supported if invaded by Germany!

The Belgian's would likely think it's a bluff, even when the French and British start digging defences on the French Belgian border (as OTL). But when the brown stuff hits the fan in May and the Begains beg for support, the response from thr WAllies is at most a very limited advance into Western Belgium (perhaps only by light reconesance forces). In this case, the Belgian's likely put up a token defence, and then the German's slowly advance to the French defensive line a couple of days later. A bonus of this is that the Dutch retreat behind the Waterline and continue to fight (at least as long as there is other more pressing objectives for the German's).

Not falling for the bait means the French aren't distracted by the heavy fighting in Belgium (as OTL) and many of their best units (on the French Boarder with Begium) are in close to the right position to intervene on the right flank of the Sicle Cut. Further its inconceivable that the Allies wouldn't notice that the majority of the rightly feared Panzers are not in Central Belgium but motoring through the Ardennes. In that case the Centre would be reinforced faster than OTL (the French Cavalry Corps would in this scenario be available and roughly in the right place) and the battle of Sedan would be very different.

Another option (although it works best in conjunction with what's above) is for Gamlin to actually concentrate a strategic reserve. IOTL each French Army and Army Group had some reserve formations so this not only is potentially doable, it has always completely mystified me why it wasn't done in OTL. If a strategic reserve was available it could at best have closed the gap in the line created by the Panzer Divisions or at worst slowed down the German advance to allow the forces in the North to move south and avoid being cut off. If this had happened OTL then although I think the Germans would have won (lots of good arguements made for this up thread), a better performance in the first stage of the Battle of France would have made a retreat to North Africa more likely as the position France found itself would not have appeared so helpless.