The battle of Cantigny (May 28 - 31, 1918) was America's first division sized engagement during the First World War; George Marshall would later opine that the objective was "of no strategic importance and of small tactical value". General Pershing was hellbent on eradicating from the popular memory any mention of the A.E.F.'s poor performance at Seicheprey some weeks earlier, and Cantigny was as good a battleground in which to do it as any. Assessing the battle two weeks after the Armistice, Pershing's "yes men" at the STARS AND STRIPES wrote:
"But at Cantigny it had been taught to the world the significant lesson that the American soldier was fully equal to the soldier of any other nation on the field of battle."
Click here to read about the foreign-born soldiers who served in the American Army of the First World War.
The American performance at the battle of Chateau-Thierry proved to General Foche that the Americans had the necessary stuff, and it was widely recognized that the Doughboys played the key roll in keeping the Germans out of Paris.
The attached STARS AND STRIPES article is extremely detailed as to the individual units (both French and American) that participated in rolling back the Germans along the Marne.
"On June 4, the best information available indicated that the enemy was employing not less than 33 divisions, about 3000,000 men...But like the defenders of Verdun, the American machine gunners set their teeth and said, 'They shall not pass.'"