The St. Mihiel Offensive began on September 12, 1918. It was the first operation of World War I performed and commanded solely by an American Army. The whole idea of the operation was to reduce the size of the German salient, a part of their battle line that jutted out towards allied territories. Though delayed at first by other occurring battles, the operation began on August 10, 1918 when the American First Army headquarters was set up. August 30, 1918, the First Army, under the direction of General Pershing took command of the battle fro ....