Following the United States entry into World War I, Koehler was promoted to lieutenant on June 5,1917 and was re-assigned to a submarine chaser squadron in the Irish Sea.
Following the United States entry into World War I, Koehler was promoted to lieutenant on June 5,1917. He was promoted to temporary lieutenant commander on July 1,1918 and was re-assigned to a submarine chaser squadron in the Irish Sea.