On July 26, 1861, Barnes was commissioned a
colonel in the
18th Massachusetts Infantry. On April 4, 1863, Barnes was promoted to
brigadier general,
U.S. Volunteers, with date of rank established as November 29, 1862. At the
Battle of Chancellorsville in May, Barnes' brigade was not heavily engaged. Late in the battle, his division commander, Brig. Gen.
Charles Griffin, fell ill, and Barnes assumed command of the 1st Division on May 5, 1863. ==Postbellum career==