The Dyle Plan or D Plan was the primary war plan of the French Army to stave off the expected German attack during Fall Gelb. It was conceived by French General Maurice Gamelin in 1940. Named after the Dyle River, which flows from southern Belgium down to Antwerp, the main objective of the plan was to halt the advancing German Army Group B, (which was incorrectly perceived as the strongest), in central Belgium. France had signed a military treaty with Belgium in 1920 to streamline communication and fortification efforts in the event of a German attack, but in October 1936 Belgium changed her policy to one of strict neutrality, limiting coordination of defense plans with France.