The German Armies lines included a salient that included the town of Saint Mihiel. The American Expeditionary Force under the command of General Pershing requested the task of attacking the salient and capturing the town. It was to be the debut of the American 1st Army in combat.
The attack began on September 12th in a coordinated assault from three sides. The allied had overwhelming air superiority with 1,481 planes manning the skies, 40% of the pilots were American. The American forces had a 144 tanks commanded by Major Patton. That was part of larger force of tanks that included over 400 tanks.
The plan was meticulously executed and had caught the German by surprise. They were in the process of withdrawing the salient. By the morning of the second day of the battle, troops advancing from both sides of the salient had met and by the end of the day all of the objectives of the army had been reached.
Allied casualties that day were 7,000 including 4,500 killed. German casualties were 22,500, of those only 2,000 were killed but 10,500 became prisoners. The battle established American Armies reputation as a effective fighting force.