Army of the Cumberland The Army of the Cumberland was one of the principal Union armies in the Western Theater during the American Civil War . It was originally known as the Army of the Ohio . History . The origin of the Army of the Cumberland dates back to the creation of the Army of the Ohio in November 1861 , under the command of Brig . Gen . Robert Anderson . The army fought under the name " Army of the Ohio " until Maj . Gen . William S . Rosecrans assumed command of the army and the Department of the Cumberland and changed the name of the combined entity to the Army of the Cumberland . When Rosecrans assumed command , the army and the XIV Corps were the same unit , divided into three wings commanded by Alexander McCook ( Right Wing ) , George H . Thomas ( Center ) , and Thomas L . Crittenden ( Left ) . General Orders No . 168 was the order passed by the Union Army on October 24 , 1862 , that called for the commissioning of the XIII Corps and the XIV Corps into the Army of the Cumberland under the command of Maj . Gen Ulysses S . Grant . The army ' s first significant combat under the Cumberland name was at the Battle of Stones River . After the battle the army and XIV Corps were separated . The former Center wing became XIV Corps , the Right wing became XX Corps , and the Left wing became XXI Corps . Rosecrans still retained command of the army . He next led it through the Tullahoma Campaign and at the Battle of Chickamauga , after which the army became besieged at Chattanooga . Maj . Gen . Ulysses S . Grant arrived at Chattanooga to assume command of the Army of the Cumberland , Army of the Tennessee , and reinforcements from the Army of the Potomac . Rosecrans had been a popular and respected commander , but because of his defeat at Chickamauga and inability to lift the Confederate siege , Grant chose to replace him with George H . Thomas on October 28 , 1863 . In the Battles for Chattanooga , Grant had been leery of using the Army of the Cumberland in the main fighting , fearing their morale to be too low after the defeat at Chickamauga . Instead , he used the veterans from the Army of the Potomac , proud of their recent victory at the Battle of Gettysburg , to take Lookout Mountain and planned to use the troops from the Army of the Tennessee , also recent victors at the Siege of Vicksburg , to attack the Confederate right flank on Missionary Ridge . The Army of the Cumberland was given the minor task of seizing the rifle pits at the base of Missionary Ridge . However , once they achieved their objective , four divisions ( one led by Philip H . Sheridan ) stormed up the ridge and routed the Confederate center . When Grant angrily asked who had ordered those troops up the ridge both Thomas and Gordon Granger , a corps commander in the army , responded they did not know . Granger then replied , " Once those boys get started , all hell can ' t stop ' em . " After Grant ' s victory at Chattanooga earned him promotion to general - in - chief of the U . S . Army , Maj . Gen . William T . Sherman assumed command of Grant ' s Military Division of the Mississippi , which controlled all Union armies in the West . He created an " army group " of the Army of the Cumberland , the Army of the Tennessee , and the Army of the Ohio and marched towards Atlanta in May 1864 . On the way to Atlanta they fought in many battles and skirmishes including the Battle of Kennesaw Mountain . In September , Atlanta fell to Sherman ' s army group . When Confederate general John B . Hood moved north from Atlanta , Sherman chose not to follow him and instead dispatched some of the Army of the Cumberland ( IV Corps and Provisional Detachment ) and the Army of the Ohio ( XXIII Corps ) after him . Thomas finally met Hood at the Battle of Nashville and crushed him , thus bringing to an end any significant military actions for the Army of the Cumberland . Other elements of the Army of the Cumberland ( the XIV and XX Corps ) marched to the sea and north through the Carolinas with Sherman , under the command of Maj . Gen . Henry W . Slocum . These forces became the Union ' s Army of Georgia and participated in the Grand Review of the Armies in Washington , D . C . , before President Andrew Johnson in 1865 .