The best strategy (Plan E) was Belgians stand firm on their front on Meuse and Albert Canal while Allies stand firm on French frontier or at the most swing their left hand slightly forward to the line of the Scheldt i/o rushing to their aid.
But it has been reached to carry out General Gamelin’s plan D (Dyle Plan) since those days of Sep 1939.
1st Group of Armies, under General Billotte, consisting of 51 divisions, stretched from the end of the Maginot Line near Longwy to the Belgian frontier, and behind that frontier to the sea in front of Dunkirk.
2nd and 3rd, under General Pretelat and Besson, consisting 43 divisions, guarded the French frontier from Longwy to Switzerland.
9 French divisions occupied the Maginot Line.
If Belgium and Holland became involved, this number would increased by 22 divisons.
total 135 divisions
More than half of the French Army stood on the southern and eastern sectors of France, 1st Group of Armies have to face the outslaught of 70 hostole divisions under Bock and Rundstedt between Longwy and the sea. To meet the connon-prof tank and dive-bomber aircraft, French deplayed about 2300 tank, mostly light.
During the night of May 9-10, German armies advance storm troop with light artillery towards France across the frontiers of Belgium, Holland and Luxembourg. Holland and Belgium, assaulted without the slightest pretext or warning, cried aloud for help. The Dutch had trusted to their water-line and Dutch frontier guards fired upon the invaders. The Belgians succeeded in destroying the bridges of the Meuse, but the Germans captured intact two across the Albert Canal.
By Plan D, 1st Allied Army Group, under General Billottee, with its small but fine British Army, advance east to Belgium once it under attack to forestall the enemy and stand on the line Meuse-Louvain-Antwerp. In front of the line, lay the main Belgian force.
at 6:45am, General Gamelin ordered the execution of Plan D.
Dutch government had placed too much confidence on their water defence but in a single day all the outer line of the Dutch defences was mastered. The whole country was under the threat of German air force. Rotterdam was reduced to a blazing ruin. The Dutch hope that they would be by-passed by the German right-handed swing as in the former war was vain.
However, Dutch people rallied to the cause with indomitable. Their Queen Wilhelmine and her family were brought to Britain safely and from there encouraged her people to defense their country. Dutch ships were placed unreservedly under British control.
While situation in Belgium was more complicated. For many years, Belgium had cherished their neutrality. Before WWII, Belgium was not impressed by British peace making and French internal problems, decided to maintain strict neutrality and bet on German good faith. When invaded, they placed their forces against invaders and not willing to let Allied enter their country. They had lose the Albert Canal and were falling back to the line of the river Gette, taking up position from Antwerp to Louvain.
The Allies and arm of Holland and Belgium were almost defeated. France prepared to evacuate Paris. Churchill flight to Paris to have meeting with French General. The problems were quite critical: on one hand the armoured vehicles of Germany were very powerful, on the other hand, there was no strategy reserve of France.
It is a hard decision whether British should send more fighter to France. With support from the Cabinet, they gave an answer of yes.