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.
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.
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 Neufchateau.
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 21 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.
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, 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, only becoming 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.