In April 1861, Sanborn was appointed as the
Adjutant General of Minnesota. His duties included overseeing the organization and equipping of three
regiments of volunteer
infantry for the fledgling Union army. He became the
colonel of the
4th Minnesota Infantry in December 1861. The regiment had been mustered into Federal service by companies at
Fort Snelling between October 4 and December 23. Sanborn and his men moved to Benton Barracks in
St. Louis, Missouri, on April 23, 1862. Sanborn led the 1st Brigade, 7th Division of the
Army of the Mississippi in
Maj. Gen. Henry Wager Halleck's
Siege of Corinth,
Mississippi, from May 18 to May 30, the
Battle of Iuka, September 19 and then in the
Second Battle of Corinth, Oct 3-4 of that year. Sanborn's brigade fought in
Ulysses S. Grant's Central Mississippi Campaign from November 1862 to January 1863. That was followed by Grant's
Vicksburg Campaign, with the
Battle of Port Gibson on May 1, the
Battle of Raymond eleven days later, and the
Battle of Jackson on May 14. Sanborn also participated in the subsequent
Battle of Champion's Hill, the
Battle of Big Black River, and the
Siege of Vicksburg from May 18 to July 4. During part of the time, he commanded a
division. Sanborn's men performed garrison duty at Vicksburg following the surrender. On August 4, 1863,
President Abraham Lincoln appointed Sanborn to the grade of
brigadier general of volunteers to rank from that date. In October of that year the
U.S. War Department named him as the commander of the District of Southwestern Missouri. He played a key role in helping defeat the forces of
Confederate Maj. Gen. Sterling Price during his
Missouri Raid. On February 10, 1865, President Lincoln appointed Sanborn to the grade of
brevet major general of volunteers, to rank from that date, and the United States Senate confirmed the appointment on February 20, 1865. Sanborn was mustered out of the volunteers on April 30, 1866. ==Reconstruction era career==