 In October 1923, Loper was posted to the 11th Engineers in the Panama Canal Zone. He returned to the United States in December 1926 and was with the Engineer Reproduction Plant at the Army War College until 31 August 1929. He then went back to Camp A. A. Humphreys, first as a student, and then, 1 September 1930, as an instructor. In December 1933, he became Assistant to the District Engineer at Omaha, Nebraska, where he was promoted to captain on 25 May 1935. In February 1938, he was posted to the 6th Engineers at Fort Lawton, Washington.
