Late on September 20, Union survivors of the battle of Chickamauga started filing through Rossville Gap to refuge in Chattanooga. Days later, Gen. Braxton Bragg's Confederates perched on hills around the town and waited for Maj. Gen. William S. Rosecrans' Union Army of the Cumberland to evacuate. With the Tennessee River at their back, fearing annihilation if it left the safety of Chattanooga, The Union army covered its front with trenches and rifle pits and waited for relief.
In Washington, President Lincoln was despondent over his crushed Army of the Cumberland and on the 25th, dispatched Maj. Gen. Joseph Hooker and 2 Virginia corps to its aid. With his cabinent, he discussed removing Rosecrans from command.
Bragg's patience was exhausted by October 1. If Rosecrans would not march out of Chattanooga, he would starve him out. Confederates held Missionary Ridge along the town's northeast-southwest front, Lookout Mountain on the southwest, and Racoon Mountain and Lookout Valley to the west. All rail lines were cut and all river traffic stopped. Bragg ordered Brig. Gen. Joseph Wheeler's cavalry to mangle remaining remaining Union supply lines. Wheeler's Raid on October 1-9, destroyedwagon trains bringing supplies to Chattanooga by the only open route, 60 twisting miles of bad road leading northwest from Bridgeport, Alabama, a town only 26 linear miles from the Federals. The Army of the Cumberland went on reduced rations and settled in for the Seige of Chattanooga.
On the 16th, the Union Military Division of the Mississippi was created and Maj. Gen. Ulysses S. Grant was named its commander. Lincoln and Sec. of War Edwin M. Stanton left Rosecrans' future to Grant, who relieved him, appointed Maj. Gen. George H. Thomas commander of the Army of the Cumberland, then traveled to Chattanooga, arriving on the 23rd. After consulting with Thomas and Chief Engineer Maj. Gen. William F. Smith, and finding an inventory showing only a few cartridges for each Federal, Grant agreed to a bold plan to break the seige. Smith proposed throwing infantry over a neck of land called Moccasin Point, on the river west of town. Other troops would travel on the Tennessee River to Brown's Ferry, a point opposite the Federals at Moccasin Point. Together they would assault Confederates on the west bank, establish a bridgehead, and hold on.
Hooker's men arrived at Bridgeport in mid-October and awaited orders. By Smith's proposals, they would move up Lookout Valley, meet the Union bridgehead, and drive Confederates from Racoon Mountain in their front. Supplies would travel the shorter water route from Bridgeport to Brown's Ferry, then be hauled across Moccasin point to hungry Chattanooga troops. The system was named the "Cracker Line".
Grant approved the plan. Cracker Line Operation went into effect on the 26th. The bridgehead was made on the 27th, Hooker linked up on the 28th, and the first steamboat arrived on November 1. A bloody, indecisive engagement resulted: Hooker left a division in his rear at Wauhatchie on his march to Moccasin Point. Confederates assaulted it in the "Wauhatchie Night Attack" on October 28-29. Though they were resupplied, the fight at Wauhatchie reminded Federals that they were not secure.
Wanting action, the Confederates surrounding them were unhappy with Bragg's tactics. Dissenting commanders Lt. Gens. Leonidas Polk, Daniel H. Hill, and Thomas C. Hindman were relieved. Lt. Gen. James Longstreet, 2 divisions, and 35 cannons were sent to invest Maj. Gen. Ambrose E. Burnside's Knoxville garrison on November 4, reducing Confederate numbers even as Federals prepared for battle.
Maj. Gen. William T. Sherman arrived in Chattanooga on November 14; his 17,000 man column from the Memphis and Vicksburg garrisons waited at bridgeport, having traveled by railand foot from Memphis. They had been assigned by Gen.-in-Chief Maj. Gen. Henry W. Halleck to relieve Chattanooga and repair damaged rail lines as they approached. Grant, impatient to attack, cancelled Halleck's order, telling Sherman to rush ahead. In Chattanooga, Sherman reconnoitered the north end of Missionary Ridge, received battle plans from Grant, returned to Bridgeport, then marched his column up Lookout Valley to Brown's Ferry.
Earlier that month, Grant had ordered an attack on the Confederates holding Missionary Ridge, but Thomas had declined, claiming his 40,000 troops were insufficient to hold the town and attack simultaneously. Sherman's fresh troops made attack possible on the 23rd, when 2 Union divisions marched out of town dressed as for military parade. Confederates on a foothill below Missionary Ridge came out to look at the pageant. The divisions rushed them, beating the Confederates from their forward position on Orchard Knob. Thomas sent more troops to support the victors, and the entire army moved ahead to dig a new trench line.
On the 24th, contenders fought the day-long battle for lookout Mountain. Hooker's 3 divisions assaulted the stronghold in the morning, and by 10:00 A.M., heavy fighting had begun in fog and mist that covered the battle scene all day. Three of Sherman's divisions crossed the Tennessee River at Brown's Ferry and marched behind Chattanooga to the Confederate right at the north end of Missionary Ridge. Thomas' remaining troops held the Union center. Once Hooker took Lookout, his men were to march south and approach Bragg's left rear on Missionary Ridge. Sherman would assault the Confederate right, Hooker would move on Confederates from the south end of the ridge., and Thomas would either hit the center or reinforce wherever the Union lines might falter.
The day was a qualified Union success. By evening, Sherman had won foothill positions on the north face of Missionary Ridge and Hooker was moving toward Bragg's left. The day-long fog kept many guessing about results on Lookout Mountain, but on the morning of the 25th, the Battle of Missinary Ridge began with a Union flag flying from the summit of Lookout Mountain.
Grant's fight for Missionary Ridge ended past 4:00 P.M. after an all-day struggle for the slopes by Sherman's force and a final, unplanned rush on the last Confederate line by Thomas' troops at the Union center. Bragg's men were routed from the ridge and forced to retreat sotheast toward Dalton, Georgia. Through the 26th, Federals pursued them to Chickamauga Creek. Hooker caught some elements near Rossville but could not bring them to a stand. The Confederates had been pushed out of south Tennessee, giving Sherman a base from which to launch his Atlanta Campaign the next spring. The Chattanooga Campaign ended with Federals believing in the prospect of a final victory in 1864.
Shortly after Bragg's defeat, Longstreet returned to Virginia, and practically all of Tennessee was cleared for the Union. With Chattanooga available as a base of operations, the way was open for an invasion of the lower South. There was a lull in major operations until the spring of 1864.