The Aisne-Marne Offensive was the second phase of the Second Battle of the Marne (15 July-6 August) and marked a major turning point in the fighting on the Western Front in 1918. The first phase of the battle had been the German Champagne-Marne Offensive, which had begun on 15 July with attacks east and west of Reims. The attacks east of the city had met with little success, but the attack to the west, by the German Seventh Army under General Max von Boehn, had advanced four miles, creating a beachhead on the southern side of the Marne. At its greatest extent the German salient reached from Soissons in the north west, to Château Thierry at its south west corner and then east along the Marne.
One positive result of the earlier German successes had been the appointment of Ferdinand Foch as overall Commander in Chief on the Western Front. Even before the German offensive on the Marne he had been planning a massive counterattack in the area. This was to involve four French armies attacking all around the salient created during the Third Battle of the Aisne. The main attack was to come from the west and would be launched by the French Tenth Army (General Charles Mangin) with the Sixth in support to his south (General Jean Degoutte). Further around the line the Fifth (General Henri Berthelot) and Ninth (Genereal M. A. H. de Mitry) would launch supporting attacks on the southern flank of the German salient.
This would be an Allied attack, with British and Italian Divisions involved. It would also be a major American battle. The American 1st and 2nd Divisions were with the Tenth Army, while the Sixth and Ninth Armies each contained three American Divisions. These were massive formations, each containing 28,000 men, making them twice the size of their British, French or German equivalents. The attack would be supported by 350 Allied tanks.
The main attack was launched on 18 July by Mangin, with fourteen divisions from the Tenth and Sixth armies. All around the line the Allies advanced between two and five miles. That night the Germans were forced to retreat back across the Marne. The rapid Allied advance threatened German communications within the salient and even offered the chance of trapping the German troops around Château Thierry. Facing with this massive Allied counterattack Ludendorff ordered his troops to pull out of the salient to form a new defensive line along the line of the Aisne and Velse rivers. The new line began to take shape on 3 August, the day after Soissons had been liberated. On 6 August the Americans probed the new line and were repulsed, ending the offensive.
The Aisne-Marne offensive marked a key turning point in the fighting of 1918. It ended the series of German victories that had begun on the Somme in March 1918 and opened the way for the great Allied offensive that would start at Amiens on 8 August. Ludendorff’s great gamble to end the war before the full strength of the American army could be deployed had failed.