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I always thought that the reason the French lost in 1940 was due to not concentrating their mechanized units. Germany had more armored divisions while France kept most of them integrated with their infantry divisions. The Panzer I sucked and the Panzer III's E variant was kind of lackluster (it was supposed to be able to deal with armor, but German crews found that against French tanks they either needed to lure them into an ambush or driver dangerously close to penetrate).

General Gamelin initially planned on advancing to the Dyle River and establishing a 680 km defensive front line.

Later, for some reason, he decided to extend the line to Breda, and some historians call this "Dyle PLan, Breda Variant" or something close depending on your book. This lengthened the line 50 kilometers, meaning more frontage to defend when the expected stalemate started. This also had the effect of dumping almost the entire Norther Theater's reserves into the effort to reach Breda.

His reasoning was that observers from the Polish campaign noticed that Polsih reserve infantry never really got to organize while being bombed from the air. Gamelin expected the Germans to have air superiority and his reaction to the Polish Campaign was "well, if airpower makes reserves worthless, I might as well send everyone to the front." At least this was one reasoning I think he made, given his comments on the Polish campaign.

Germany did not attack on the Belgian Planes but through the Ardennes. The French did not anticipate an attack here and were defeated in the Battle of Sedan. The German Armored Spearheads went waaaay ahead of the infantry and logistical bottlenecks prevented the German infantry from catching up immediately.

Well, I'm just wondering, how much of this defeat was due to poor French tank doctrine or just the fact they put all their eggs in the Breda basket.

If they went with the original Dyle plan and only mobilized their reserves after something similar to Sedan, would they be able to destroy he German Armor? Let's suppose everything up to Sedan is similar to OTL, only the French elite units (1st Light mechanized, 3rd Light Mechanized 25th Motorized, 3rd Motorized, 60th infantry, 21st infantry, and 61stinfantry) are sitting in reserves just north of the Belgian boarder (away from the fighting and fully organized) instead of racing towards Breda (where they were still away from the main fighting aside from sporadic skirmishes, but disorganized in their rush north). Most of their tanks are integrated with infantry units are were not designed to move faster than infantry (and their supply was not designed to move faster than an infantry advance).

But shouldn't infantry divisions with integrated armor and tanks should be able to beat the German Armor after entrenching themselves? The French tanks usually had powerful guns. And the Belgian 37 mm guns and the French 47 mm field guns both easily penetrated German tanks on the front.

Using tanks as infantry support might not be using their whole potential, but I think the French could have recovered from Sedan if they didn't put so many units in Belgium trying to get to Breda.
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