At the outbreak of the Civil War, Smith became a
colonel of the
2nd California Volunteer Cavalry in the
Union Army, rising early in 1862 to the rank of
brigadier general in the United States Volunteers and to the chief command of the cavalry in the Department of the Missouri. From March through July, he served in the same capacity in the Department of the Mississippi. Assigned afterwards to the
Army of the Tennessee, he took part in the
Battle of Chickasaw Bayou and the capture of
Arkansas Post. He commanded a division of the
XIII Corps in the
Vicksburg campaign. Later, he led a division of the
XVI Corps in the
Red River campaign of Maj. Gen.
Nathaniel Banks. He received the
brevet rank of colonel in the
Regular Army for his services at the action of
Pleasant Hill. Smith became a
lieutenant colonel in the Regular Army in July 1864, to rank from May 9. In July, 1864, Smith led
an expedition into Mississippi. On July 14–15, he defeated Confederate Lt. Gen.
Stephen D. Lee at the
Battle of Tupelo, where Lee took over general command over the Confederate forces on the field from General
Nathan Bedford Forrest. In retaliation for Forrest's raid on
Fort Pillow, north of Memphis, Union General Andrew Jackson Smith, with a large military force, arrived in Oxford, Mississippi on August 24, 1864, and in one day burned the Lafayette County Courthouse, all the business houses on the Square, except one, and all homes in the immediate area. During the autumn of 1864, Smith lead Union troops against Confederate Maj. Gen.
Sterling Price during
Price's raid into
Missouri. Smith was then summoned to join forces with Maj. Gen.
George Henry Thomas at
Nashville, Tennessee, then threatened by the advance of Confederate Lt. Gen.
John Bell Hood. Smith bore a conspicuous share in the crowning victory at the
Battle of Nashville leading his troops past the Confederates' south flank. He commanded the XVI corps in the final campaign against
Mobile, Alabama, in 1865. On April 10, 1866, President
Andrew Johnson nominated Smith for appointment to the grade of brigadier general in the United States Army (Regular Army), to rank from March 13, 1865, for his services at the Battle of Tupelo and the United States Senate confirmed the appointment on May 4, 1866. On the same dates, President Johnson nominated and the United States Senate confirmed Johnson's appointment of Smith as brevet major general in the Regular Army, to rank from March 13, 1865, for his success in leading his men at the Battle of Nashville. The Senate reconfirmed this appointment on July 14, 1866, after recalling the confirmation and return of the nomination to President Johnson for possible readjustment of the date. ==Postbellum life==