Buell chose to defend the Union cause and entered the volunteer ranks of his birth state in 1861. On December 17 he was appointed to the rank of lieutenant colonel in the 58th Indiana Infantry. He was promoted to colonel on June 24, 1862.[1] Buell led the 58th Indiana during the Battle of Perryville on October 8.[2] Buell then led his regiment during the Battle of Stones River in late December into January 1863. During the fight he took over command of Brig. Gen. Milo S. Hascall's brigade when that officer was needed for division command, and Lt. Col. James T. Embree then led the 58th Indiana.[3] After the battle Buell was given brigade command and led several different brigades in the Army of the Cumberland throughout 1863 and 1864.[4] He also led a brigade during the Battle of Chickamauga on September 19–20, 1863.[5]
Buell elected to continue in the U.S. Army after the Civil War. He was promoted to lieutenant colonel in the regular army on July 28, 1866, in the 29th U.S. Infantry Regiment. Buell was appointed a brevet colonel in the regular army to rank from March 2, 1867, a reward for his performance in November 1863 at Missionary Ridge during the war.[10] On December 3, 1867, PresidentAndrew Johnson nominated Buell for appointment to the grade of brevet brigadier general in the regular army, to date from March 2, 1867, and the United States Senate confirmed the appointment on February 14, 1868.[11]
^Eicher, 2001, p. 152. 2nd B, 1st D, Left Wing, XIV Corps, Army of the Cumberland (Dec 31, 1862 – Jan 9, 1863); 1st B, 1st D, XXI Corps, Army of the Cumberland (June 10 – July 25, 1863, and again from Aug 3 – Oct 9, 1863); Pioneer B, Army of the Cumberland (Oct 9, 1863 – June 17, 1864)
^Eicher, p. 152. 2nd B, 1st D, XIV Corps, Army of Georgia (Jan 17 – March 28, 1865, and again from April 4 – June 17, 1865); 1st D, XIV Corps, Army of Georgia (March 28 – April 4, 1865, and again from June 17 – June 27, 1865).