Cavalry, Frank M. Andrews, who was engaged to the daughter of Brigadier General James Allen. While serving as one of Andrews' groomsmen, Brett met Mary Devol, one of the bridesmaids, and the daughter of another Army officer, Major General Carroll A. Devol. Brett married Mary Devol in Denver on 1 March 1916. Influenced by Allen and Andrews, Brett transferred to the Aviation Section, U.S. Signal Corps on 2 September 1916. He attended aviation school and on graduation in 1916 was assigned to the office of the Chief Signal Officer in Washington, D.C. where he was promoted to first lieutenant on 1 July 1916 and captain on 15 May 1917.