During World War I, Drum was chief of staff for First United States Army, and led the planning for First Army's participation in the Saint Mihiel and Meuse-Argonne offensives. He was promoted to temporary brigadier general and received the Army Distinguished Service Medal. After the war, Drum commanded 1st Infantry Brigade, 1st Infantry Division, Fifth Corps Area, and the Hawaiian Department. Having served as the Army's Deputy Chief of Staff and Inspector General, Drum was a candidate for Army Chief of Staff in 1939 but the position went to George Marshall. Drum received promotion to lieutenant general in August 1939, and commanded the Eastern Defense Command during the early years of World War II. He reached the mandatory retirement age of 64 in 1943, after which he was commander of the New York Guard (1943–1948), and president of Empire State, Inc., the company that managed the Empire State Building (1944–1951).