On the 4th of July 1918, the American I Corps assumed command of a portion of the Chateau-Thierry sector, which included the US 1st Infantry Division. These troops would be the first Americans to see combat in WWI.
On the 4th of July 1918, Lieutenant Colonel Hugh A. Drum was selected to be the Chief of Staff for First US Army. This would see the first formal organization of the future First U.S. Army.