Upon his promotion to brigadier general, Johnson was appointed director of the Purchase and Supply Branch of the General Staff in April 1918, and was promoted to Assistant Director of the Purchase, Storage and Traffic Division of the General Staff in October 1918. In this capacity, he worked closely with the War Industries Board. He favorably impressed many businessmen, including Bernard Baruch (head of the War Industries Board). These contacts later proved critical in winning Johnson a position with President Franklin D. Roosevelt's administration. He was put in command of the 15th Infantry Brigade which was part of the 8th Division, but the unit did not deploy to Europe because the war had ended.