Sawtelle served as chief quartermaster of Union forces in Brownsville, Texas from February to April 1864. In May and June 1864, he supervised troop and supply transports during the relief of troops commanded by Nathaniel P. Banks at the end of the Red River campaign. In May, he was promoted to lieutenant colonel of Volunteers for the second time. Sawtelle was assigned as chief quartermaster of the Military Division of West Mississippi from June 1864 to June 1865. In June and July 1865, he served as chief quartermaster of the Military Division of the Southwest. In May 1865, he was promoted to colonel of Volunteers. At the end of the war, Sawtelle received brevet promotions to major, lieutenant colonel, colonel, and brigadier general to recognize the superior service he rendered throughout the war.
