Accompanying his brother, Charles Ellet, as an aide-de-camp, in 1861, Alfred joined the ranks of the Union army as a lieutenant colonel. He helped his brother, who was an engineer, to convert ships into rams to go into battle against ironclads. On June 6, 1862, they both served at Memphis and his brother died of his wounds. Afterward, Alfred served with the Department of Mississippi, including service with the Marine Brigade in 1863. Alfred continued in this capacity until December 31, 1865, when he resigned his commission and returned home.
