The Champagne-Marne Offensive, 15-18 July 1918, was the last of Ludendorff’s five offensives of 1918 that had come close to breaking the Allied lines (this offensive is often seen as part of the Second Battle of the Marne, 15 July-6 August 1918). The first two of those offensives (Second Battle of the Somme, March 1918 and the Lys Offensive of April 1918) had been aimed at the British, with the hope that a gap could be created between the British and French armies that would allow the Germans to reach the Channel ports. After Lys Offensive had failed to break through the British lines, Ludendorff decided to switch his attention to the French lines on the Aisne. This Third Battle of the Aisne was originally intended as a diversion, to draw reserves south in preparation for a new attack on the British lines in Flanders. However, the success of the Aisne offensive fatally distracted Ludendorff from his strategic objectives. While always planning to renew the offensive in Flanders, his fourth offensive (Noyons-Montdidier, June 1918) was a purely tactical affair, aimed at straightening out the German front line.
The Champagne-Marne Offensive took Ludendorff even further away from his intended field of action in Flanders. The earlier German advances had created a new salient in the French lines around the fortified city of Reims. Ludendorff now decided to launch a two pronged attack to the west and east of Reims. The two prongs would meet south of the city, pinching out the French salient. That done, Ludendorff was once again planning to move troops north to Flanders.
Three German armies and 52 divisions were allocated to the Champagne-Marne offensive. West of Reims was the Seventh Army under General Max von Boehn. To the east were the First Army under General Bruno von Mudra and the Third under General Karl von Einem.
Against them stood two French armies, the Sixth under General Jean Degoutte west of Reims and the Fourth under General Henri Gouraud to the east. The French were well aware that Ludendorff was prepared to attack, and preparations were underway to launch a massive counterattack on the Marne salient.
The attack began on 15 July. East of Reims the two German armies ground to a halt on the first morning of the battle and made no more progress. In the west the German Seventh Army did rather better. Here the French defences were rather weaker, having only been under construction since the end of May. The Germans were able to penetrate four miles across the Marne on a front nine miles long. They were then stopped by the French Ninth Army, which then included the American 3rd Division. Allied airpower began to tell, with attacks on the Marne bridges and supply lines disrupting the German offensive.
The offensive was ended on 18 July by a massive French counterattack launched by four French armies, with American, British and Italian divisions in support. This Aisne-Marne offensive would be the turning point of the fighting on the Western Front, marking the beginning of the Allied offensives that would only end with the Armistice.