Chattanooga campaign, Aug.-Nov., 1863, military encounter in the American Civil War. Chattanooga, Tenn., which commanded Confederate communications between the East and the Mississippi River and was also the key to loyal E Tennessee, had been an important Union objective as early as 1862 (see Buell, Don Carlos). In 1863, the Union general William Rosecrans, commanding the Army of the Cumberland, forced Braxton Bragg to withdraw his Confederate army from middle Tennessee (June-Aug.) and maneuvered him out of Chattanooga (Aug. 16–Sept. 8). Deceived into believing that Bragg was retreating upon Atlanta, Rosecrans pursued and was trapped by the Confederates at Chickamauga Creek, c.12 mi (20 km) S of Chattanooga. Strengthened by James Longstreet's corps, which had traveled some 650 mi (1,050 km) from Lee's army through Virginia and the Carolinas to join him, Bragg routed the Union right at the Battle of Chickamauga (Sept. 19–20). He could not crush the Union left under George H. Thomas, however; Thomas held off the enemy until Rosecrans ordered him to withdraw to Chattanooga. Bragg then took up a position extending along Missionary Ridge across Chattanooga Valley to Lookout Mt. and laid siege to the town. In a historic movement, Joseph Hooker and two corps from the Army of the Potomac circled nearly 1,200 mi (1,900 km) via Indianapolis to bolster the Union forces. But Rosecrans had lost control of the situation, and an alarmed federal administration at Washington called for U.S. Grant, who arrived at Chattanooga on Oct. 23, 1863. Generals W. F. Smith and Joseph Hooker executed a coup (Oct. 26–29) that restored a sorely needed supply line on the Tennessee River, so Grant was ready to move by late November. Sherman, who had brought up reinforcements from Vicksburg, commanded the left; Thomas, the center; and Hooker, the right. Bragg's forces had been weakened by the departure of Longstreet on an unsuccessful expedition to Knoxville. On Nov. 24, Hooker drove the Confederates from Lookout Mt. in the Battle above the Clouds. On Nov. 25, Sherman could make no headway against Missionary Ridge from its northern end, so Grant ordered the center to advance. Thomas's men—Philip Sheridan conspicuous among them—displayed great courage and boldness, proceeding to carry Bragg's position at the top; there Hooker's forces joined them in routing the Confederates. By nightfall Bragg was in full retreat to Georgia. The victory left Chattanooga in Union hands for the rest of the war.
See study by M. H. Fitch (1911); F. Downey, Storming of the Gateway (1960, repr. 1969).