Remaining in the army after the war, which ended on November 11, 1918, and in the subsequent interwar period, Coulter served in the War Department's Personnel Branch, and then assumed command of the 2nd Squadron, 14th Cavalry Regiment at Fort Des Moines, Iowa. In 1922 he graduated from the U.S. Army Cavalry School and was assigned to the War Department as the Cavalry chief of materiel, later serving as executive officer (XO) to the Chief of Cavalry.