The French believed a small covering force in the rough terrain would be enough to delay a German advance through the hilly, forested terrain of the Ardennes for at least nine days. The Belgians had two light divisions under General Maurice Keyaerts defending an 85km front, and the French planed to move two cavalry/light mechanized divisions and a calvary brigade into the Ardennes.

The Belgians insisted on maintaining their neutrality, and this meant there was poor coordination between the French and Belgian military. The Belgians were mainly concerned at preventing the Germans from moving through the Ardennes and flanking their main defensive lines. Their plan in the Ardennes was to detonate explosives to fell trees and create obstacles along the roads, then withdraw to the northwest and defend along the Namur River. The main resistance offered to the Germans was from two companies of the Chasseurs Ardennais. One never received the withdraw order when their sister company's demolitions cut their communication lines. The other's withdrawl was blocked when troops of the Großdeutschland regiment were airlanded behind their position. The obstacles were quickly cleared, and demolished bridges repaired.

The French covering force advanced to establish defensive lines to prevent a German force moving in from eastern Belgium. They were bewildered to encounter Belgian forces falling back, having planned on reinforcing the Belgian defense. Because they anticipated the Germans coming from the northeast, their defensive lines were to run from northwest to southeast. The Germans, however, were coming from Luxembourg, due east. In most cases, they were flanked before they even reached their objectives, and narrowly avoided having their lines of retreat cut off. A few French units that did manage to offer resistance were bypassed and forced to withdraw.

Instead of 9-10 days, the Germans reached the Meuse River by then end of the second day.

The Breaking Point: Sedan and the Fall of France, 1940 By Robert A. Doughty