Having earned their spurs at Château-Thierry and Belleau Wood, American troops were assigned increasingly important parts during the German’s summer offensive.  More than 25,000 Yankees manned the left side of the Allied lines when Germany attempted to crash through along a 20-mile front stretching between Montdidier and Noyon on 9 June. And more than 270,000 would fight in the tide-turning Second Battle of the Marne in July.

German General Ludendorff still believed that the key to victory was defeating the British in the north of France.  But success there was dependent on a French-freezing campaign near Paris along the Marne near Reims.  A massive attack there, so close to Paris, would make the French think long and hard about diverting troops to the north to support the British. 

The plan made sense, but, by now, the window of opportunity that Ludendorff had recognized in the early spring was closing fast.  American troops—fresh and battle-ready—were strengthening the tired Allied lines (the millionth American soldier reached France in July).  The war spirit among the German public was fading rapidly.  The Allied blockade forced rationing; and within these compromised conditions, the flu epidemic that was sweeping the world took a particularly devastating toll.  On a single October day, the disease killed 1700 Berliners.  The military and social conditions led to massive desertions—and this steady stream of deserters kept Allied commanders well-informed as to German military movements and objectives.

Therefore, the German attack on the Marne was far from a surprise.  The Allies deployed 34 divisions, including nine American, to meet the 52 gathered by the Germans for the attack. And hours before the German attack began, the Allies unleashed a ferocious barrage, partially preempting the German artillery assault and ripping holes in the ground attack even before it got started.  Still, the German forces were able to make some headway.  The American 3rd Division found itself all but surrounded at one point, fighting German forces on three sides.  

But the Allied lines held.  And on 18 July, the Allies took the offensive.  They hit the Germans along a 20-mile front between the Aisne and Marne Rivers. About 270,000 American troops formed the spearhead of the attack and pushed the Germans back four miles on the first day. Progress slowed after that as German artillery, initially caught by complete surprise, now re-deployed and opened up on the Allied forces.  But by 6 August, the Allies had restored the lines that preceded the Germans’ summer offensive.  Five months of fighting had achieved nothing. And the sense of opportunity that had excited German efforts in the spring was replaced by a more gloomy awareness of shrinking prospects.