At the outbreak of World War I on 2 August 1914, von Kuhl became Chief of Staff in General Alexander von Kluck's First Army which was the crucial right flank of the swinging door in the Schlieffen Plan. Kluck regarded him as a notable man, of most energetic character and wide views. Mentally and physically he was imperturbable, and, in addition to an extremely cultivated mind, he possessed a personal bravery on the battlefield which from time to time evoked a caution from the Army Commander. By adroit staff planning they squeezed their 320,000 men through a strip of land between Liege and the Dutch border. Pivoting down into France they swept back the British Expeditionary Force. Shortly thereafter they had reached the Marne River and were transferring men to their right flank to fend off a French thrust from Paris. With the tip of the Eiffel Tower on the horizon, they were sure that "complete victory beckoned" Nonetheless they were ordered to retreat because of concern about the gap between their right flank and the German Second Army abandoning the Schlieffen Plan. Kuhl always maintained that the retreat was a disastrous, unnecessary failure of nerve. He was promoted to "Generalleutnant" on 18 April 1915. On 22 September in that same year, he became chief of staff in General Max von Fabeck's Twelfth Army, which was shifted to the Eastern Front. Next starting on 24 November 1915 he served in the same capacity in the Sixth Army on the Western Front, which was commanded by General Crown Prince Rupprecht of Bavaria. Rupprecht's prewar career was in the Bavarian Army. For exemplary service during the Battle of the Somme Kuhl received the "Pour le Mérite" on 28 August 1916.