Smith was detached from the 5th Marines and sent to the Army General Staff College at Langres, from which he graduated in February 1918. He was the first of only six Marines ever to complete this course. He was then named Adjutant of the 4th Marine Brigade, which was a part of the US Army's 2nd Infantry Division, serving in a relatively quiet sector southeast of Verdun. During the fighting in and around Belleau Wood, he played "a vital though undramatic" role as brigade liaison officer, overseeing internal communications within the brigade. Transferred to the I Corps, First Army, in July 1918, he served as assistant operations officer in charge of liaison during the Aisne-Marne, Oisne-Aisne Offensive, St. Mihiel and Meuse-Argonne offensives. On 25 November 1918 Smith was promoted to the temporary rank of major.