Lee was appointed Wood's aide de camp on 23 April 1917, shortly after the United States formally declared war on Germany. Wood was offered commands in Hawaii and the Philippines, but turned them down in order to take command of the 89th Division, a newly-formed National Army division at Camp Funston, Kansas. Lee, who was promoted to major on 5 August 1917 and lieutenant colonel on 14 February 1918, became the division's acting chief of staff and then assistant chief of staff.