The Second Battle of the Marne , or Battle of Reims (15 July – 6 August 1918) was the last major German offensive on the Western Front during the First World War. The attack failed when an Allied counterattack by French and American forces, including several hundred tanks, overwhelmed the Germans on their right flank, inflicting severe casualties. The German defeat marked the start of the relentless Allied advance which culminated in the Armistice with Germany about 100 days later.