In his successful Tullahoma Campaign in the summer of 1863, Rosecrans moved southeast from Murfreesboro, Tennessee, driving Bragg across the state of Tennessee to the city of Chattanooga, suffering only 560 casualties along the way. Chattanooga was a vital city for Union war aims because seizing it would open the door for an assault on Atlanta and the heartland of the South. General-in-chief Henry W. Halleck was insistent that Rosecrans move quickly to seize Chattanooga. President Abraham Lincoln declared that "whoever controls Chattanooga will win the war." Chattanooga was also vital to the Confederate States of America. The location between Lookout Mountain, Missionary Ridge, Raccoon Mountain, and Stringer's Ridge was strategically important. In addition, Chattanooga was a rail hub (lines going northward toward Nashville and Knoxville and southward toward Atlanta), a center of banking and commerce, and a manufacturing center (iron and coke) located on the navigable Tennessee River.
Rosecrans delayed for weeks but finally renewed the offensive on August 16, aiming to force the Confederates out of Chattanooga by threatening their supply lines to the south. A major obstacle on his route was the Tennessee River, and Rosecrans devised diversionary activities to prevent Bragg from opposing his crossing at Caperton's Ferry. The Second Battle of Chattanooga was part of the diversion. Colonel John T. Wilder of the XIV Corps moved a brigade near Chattanooga and bombarded the city with artillery for two weeks, fooling Bragg as to the direction of the Union advance. Rosecrans crossed the Tennessee without opposition. The terrain he faced in northwestern Georgia was formidable, consisting of the long chain of rugged mountains known as Lookout Mountain and Missionary Ridge, which had very poor road networks.
Bragg and the Confederate high command were nervous about this development and took steps to reinforce Bragg. General Joseph E. Johnston's army dispatched a division fromMississippi under Maj. Gen. Hiram T. Walker by September 4, and General Robert E. Lee dispatched a corps under Lt. Gen. James Longstreet from Virginia.
Three corps of Rosecrans's army split and advanced by separate routes, on the only three roads that were suitable for such movements. On the right flank, the XX Corps under Maj. Gen. Alexander M. McCook moved southwest to Valley Head, Alabama; in the center, the XIV Corps under Maj. Gen. George H. Thomas moved just across the border to Trenton, Georgia; and on the left, the XXI Corps under Maj. Gen. Thomas L. Crittenden moved directly toward Chattanooga around Lookout Mountain. On September 8, after learning that Rosecrans had crossed into his rear, Bragg evacuated Chattanooga and moved his army south along the LaFayette Road toward LaFayette, Georgia. He was aware of Rosecrans's dispositions and planned to defeat him by attacking his isolated corps individually. The corps were spread out over 40 miles (65 km), too far apart to support each other.http://discussions.apple.com/thread.jspa?threadID=1078191&tstart=45 http://louis-j-sheehan.myblogvoice.com/louis-j-sheehan-102307-205296.htm
Rosecrans was convinced that Bragg was demoralized and fleeing to either Dalton, Rome, or Atlanta, Georgia. Instead, Bragg's Army of Tennessee was encamped at La Fayette, some 20 miles (32 km) south of Chattanooga. Confederate soldiers who posed as deserters deliberately added to this impression. Rosecrans ordered McCook to swing across Lookout Mountain at Winston's Gap and use his cavalry to break Bragg's railroad supply line at Resaca, Georgia. Crittenden was to take Chattanooga and then turn south in pursuit of Bragg. Thomas was to continue his advance toward La Fayette. On September 10, Thomas's advance division, under Maj. Gen. James Negley, encountered a Confederate division under Maj. Gen. Thomas C. Hindman, and a skirmish occurred at Dug Gap in Pigeon Mountain. The minor engagement became known as the Battle of Davis' Cross Roads. After the encounter, Negley's Federals withdrew back to Stevens's Gap in Lookout Mountain.
Bragg decided to attack Crittenden and ordered Maj. Gen. Leonidas Polk to attack Crittenden's lead division, under Brig. Gen. Thomas J. Wood, early on September 13, with Polk's corps and Walker's corps, assuming that Crittenden's divisions were separated. However, Polk realized that Crittenden had in fact concentrated his divisions and elected not to attack, infuriating Bragg. For the second time in three days, Bragg had been unable to get his subordinates to attack in a timely fashion, and now Rosecrans was belatedly concentrating his forces.http://www.adn.com/news/politics/fbi/anderson/story/9374361p-9286744c.html http://www.aeonity.com/ptreynolds
By September 17, the three Union corps had closed up and were much less vulnerable to individual defeat. Yet Bragg decided that he still had an opportunity. Reinforced with troops arriving from Virginia under Maj. Gen. James Longstreet, and troops from Mississippi under Brig. Gen. Bushrod R. Johnson, he decided on the morning of September 18 to advance on Crittenden's left and cut the three union Corps from their supply base at Chattanooga.
