Promoted to first lieutenant on 27 February 1912, Lee became an instructor for the Ohio National Guard, then returned to the 3d Battalion at Fort Leavenworth. In September and October 1912, he was aide de camp to the Secretary of War, Henry L. Stimson. When Stimson's chief of staff, Major General Leonard Wood asked Lee what assignment he would like next, he requested return to his battalion, which was being deployed to Texas City, Texas on the Mexican Border, where there were security concerns as a result of the Mexican Revolution.