Battle of the Ardennes The Battle of the Ardennes was one of the opening battles of World War I . It took place from August 21 – 23 , 1914 , part of the Battle of the Frontiers . Background . French commander - in - chief Joseph Joffre ordered an attack through the Ardennes forest in support of the French invasion of Lorraine . According to the pre - war French war strategy document , Plan XVII , German forces in the area were only expected to be light , with French light , rapid - firing artillery proving advantageous in a wooded terrain such as that found in the Ardennes . By 20 August , however , it was becoming clear - first to General Charles Lanrezac ' s French Fifth Army , and then to Commander - in - Chief Joseph Joffre - that a massive German presence was gathering in the area . That same day the Germans launched a counter - attack against the French advance into Lorraine . Even so , Joffre ordered an invasion of the Ardennes on 20 August for the following day . Battle . Two sets of armies joined battle on both French and German sides . General Pierre Ruffey ' s Third Army and General Fernand de Langle de Cary ' s Fourth Army fought the German Fourth and Fifth Armies : the former led by Duke Albrecht , the latter by Crown Prince Wilhelm . The two German armies together formed the centre of the German Schlieffen Plan ' s advance into France . The French Fifth Army , meanwhile , had been engaged northbound to Charleroi on the back of news of a German build - up of strength in Belgium . German troops had begun to advance through the forest on 19 August , building defensive positions as they went . Crown Prince Wilhelm was positioned at Briey with Duke Albrecht en route to Neufchâteau . The aim of the advancing French forces was straightforward : to attack the German centre in the flank as it passed through the forest of the Ardennes . With the upcoming of thick fog , the opposing forces literally stumbled into each other in the forest on 20 August ; in such fog , advanced recon was of little worth . At this early stage the French mistook the German presence for small screening forces ; in reality the French were heavily outnumbered . The first day of the battle , 21 August , was marked by scattered fighting , mostly skirmishes . Widespread battle began the following day . The advanced tactical positioning by the Germans more than offset the occasional French success , although casualties were heavy on both sides . French troops , dressed brightly , were notably conspicuous in the woods , no concession to camouflage having been considered . The French , acting with ' offensive spirit ' , charged at German positions in the woods , only to be cut down by efficient machine gun fire , backed by heavy artillery . Aftermath . In contrast to the Germans ' willingness to settle and dig trenches , the French forces began a disorderly retreat on the late afternoon of 23 August , the Third Army withdrawing to Verdun chased by the German Fifth Army ( where Ruffey was subsequently removed by Joffre ) and Fourth Army retreating near Sedan and Stenay . The latter engaged their German pursuers whilst there on 26 – 28 August ( the Battle of the Meuse ( ) ) , temporarily halting the Germans ' progress . As a consequence of the poorly managed French retreat , the Germans were able to take possession of important iron resources and were able to continue their advance into France . The scale of the French defeat was notable . For example , the French Colonial Corps , the only truly regular force in the French army , had one of its divisions almost entirely destroyed ( 11 , 000 dead out of a contingent of 15 , 000 men ) . The scale of the defeat only became clear to Joffre after a period of time had elapsed . Even then he was inclined to blame the poor performance of his forces rather than attribute it to strategy and circumstances . It did not , however , discourage him from planning further offensive attacks in future battles .