The 5th Division trained with French Army units from 1 to 14 June 1918. The first soldiers of the unit to be killed in action died on 14 June of that year. Among the division's first casualties was Captain Mark W. Clark, then commanding the 3rd Battalion, 11th Infantry Regiment, who would later become a four-star general. On 12 September, the unit was part of a major attack that reduced the salient at St. Mihiel. The division later fought in the Meuse-Argonne Offensive, the largest battle fought by the American Expeditionary Force (AEF) (and the largest in the history of the U.S. Army) in World War I. The war ended soon after, on November 11, 1918. The division served in the Army of Occupation, being based in Belgium and Esch-sur-Alzette, Luxembourg until it departed Europe. The division returned to the United States through the New York Port of Embarkation at Hoboken, New Jersey, on 21 July 1919.