On September 26, 1918, the beginning of the Meuse-Argonne Offensive with more than 1 million American soldiers taking part in the largest and most costly offensive of WWI. From the article:
"Meuse-Argonne offensive opens
At 5:30 on the morning of September 26, 1918, after a six-hour-long bombardment over the previous night, more than 700 Allied tanks, followed closely by infantry troops, advance against German positions in the Argonne Forest and along the Meuse River.
Building on the success of earlier Allied offensives at Amiens and Albert during the summer of 1918, the Meuse-Argonne offensive, carried out by 37 French and American divisions, was even more ambitious. Aiming to cut off the entire German 2nd Army, Allied Supreme Commander Ferdinand Foch ordered General John J. Pershing to take overall command of the offensive. Pershing’s American Expeditionary Force (AEF) was to play the main attacking role, in what would be the largest American-run offensive of World War I.
After some 400,000 U.S. troops were transferred with difficulty to the region in the wake of the U.S.-run attack at St. Mihiel, launched just 10 days earlier, the Meuse-Argonne offensive began. The preliminary bombardment, using some 800 mustard gas and phosgene shells, killed 278 German soldiers and incapacitated more than 10,000. The infantry advance began the next morning, supported by a battery of tanks and some 500 aircraft from the U.S. Air Service.
By the morning of the following day, the Allies had captured more than 23,000 German prisoners; by nightfall, they had taken 10,000 more and advanced up to six miles in some areas. The Germans continued to fight, however, putting up a stiff resistance that ultimately forced the Allies to settle for far fewer gains than they had hoped.
Pershing called off the Meuse-Argonne offensive on September 30; it was renewed again just four days later, on October 4. Exhausted, demoralized and plagued by the spreading influenza epidemic, the German troops held on another month, before beginning their final retreat. Arriving U.S. reinforcements had time to advance some 32 kilometers before the general armistice was announced on November 11, bringing the First World War to a close."