The Dyle Plan or Plan D was the plan of the Commander-in-Chief of the French Army, Général d'armée Maurice Gamelin, to defeat a German attempt to invade France through Belgium. The Dyle (Dijle) river is 86 km (53 mi) long, from Houtain-le-Val through Flemish Brabant and Antwerp; Gamelin intended French, British and Belgian troops to halt a German invasion force along the line of the river. The Franco-Belgian Accord of 1920 had co-ordinated communication and fortification efforts of both armies. After the German Remilitarization of the Rhineland on 7 March 1936, the Belgian government abrogated the accord and substituted a policy of strict neutrality, now that the German Army was on the German–Belgian border.

Maurice Gustave Gamelin was a French general. He is remembered for his disastrous command of the French military during the Battle of France in World War II and his steadfast defence of republican values.