In February 1915 DeSomer was promoted to the Warrant Officer rank of Gunner. During the next four years he served on the transport , the armored cruiser and the battleship . He was temporarily commissioned as an Ensign in August 1917 and attained the rank of Lieutenant in September 1918. In the Spring of 1919, DeSomer transferred to Naval Training Center, Great Lakes, Illinois. He was made a permanent Lieutenant in August 1920 and, a year later, reported to the newly commissioned battleship .