Prologue

        Rosecrans' successful Tullahoma Campaign turned Bragg out of his positions in Tenn. North of Chattanooga and opened the way for the capture of that vital communications hub. The town was too well fortified to be taken by frontal assault, so Rosecrans planned another strategic envelopment. He decided to operate west of the town, rather than to the east, so as to make the best use of the rail lines to Stevenson for supplying his forces. Bragg expected his opponent to shift his line of operations to the other side of Chattanooga, where he would be in a better position to secure the assistance of Burnside's forces in East Tennessee.
       The Confederate authorities considered another offensive into Tenn., but decided they lacked the means. They then ordered a reorganization of Bragg's forces in order to assure the defense of Chattanooga. Buckner was put under Bragg's command, and Longstreet was ordered from the Army of Northern Virginia with the divisions of McLaws and Hood to reinforce Bragg.
       After much unsuccessful urging, the authorities in Washington, on 5 August, sent Rosecrans and Burnside orders to advance and gain possession of the upper Tennessee Valley. On 15 August, Rosecrans issued orders for an advance to the Tennessee River, and Burnside ordered an advance on Knoxville and Kingston. Rosecrans' forces reached their initial objectives on 21 August and spent the rest of the month preparing to cross.
       Bragg began concentrating his forces around Chattanooga when he learned from Wheeler's cavalry that the Federals were starting to cross the river. About 1 September, he was reinforced by two divisions from the Army of the Mississippi (Breckinridge and W.H.T. Walker). Wheeler and Forrest remained in command of the cavalry carps. On the morning of the 18th, three brigades of Longstreet's corps arrived, under Hood's command. Longstreet himself arrived the next night with two more brigades. The six brigades of the eastern troops and E.P. Alexander's artillery did not arrive in time for the battle.
       Rosecrans crossed the river without opposition, completing the operation 4 September. Assuming from incorrect reports that Bragg was evacuating Chattanooga, Rosecrans advanced through the mountainous terrain on a 40-mile front to cut off Bragg's retreat. By 6 September, his three corps were in the valley of Lookout Creek, with the most advanced division in Steven's Gap. Burnside occupied Knoxville and Kingston this same day. It was also on 6 September that Bragg decided to abandon Chattanooga, concentrate at LaFayette, and defeat the Federals as they emerged from the mountain passes. Hill moved the night of the 7th to LaFayette; Polk started the next morning for Lee and Gordon's Mill; Walker joined Hill near LaFayette; and Buckner took up a position generally between the two wings.
       There followed a complex sequence of maneuvers in which the failures of Bragg's subordinates deprived the Confederates of their opportunity for defeating isolated Federal units in detail. The first failure was on the 10th when faulty coordination between the divisions of Hindman (Polk) and Cleburne (Hill) enabled Negley's isolated division at Dug Gap to be reinforced before the Confederates could attack it. Rosecrans now believed the entire enemy army was around LaFayette and started concentrating his own forces. Crittenden, who had taken Chattanooga and then moved to Ringgold, started westward on 12 September to Lee and Gordon's Mill. Walker was ordered from LaFayette to reinforce Polk and to attack Crittenden. The forces of both commanders now began to shift north. Rosecrans order McCook to withdraw from Alpine and move west of Lookout Mountain to join Thomas at Steven's Gap. Both commanders shifted troops as bits of enemy information were reported. Bragg, having missed repeated opportunities for destroying isolated Federal forces, now was content to await his reinforcements from Mississippi and Virginia.
       Bragg ordered a dawn attack for 18 September against Crittenden's corps on the Federal north flank. This well-conceived plan was frustrated by Federal mounted brigades. Bushrod Johnson's division finally succeeded in forcing a crossing against Minty's cavalry at Reed's Bridge late in the afternoon. Wilder's cavalry inflicted heavy losses on Liddell's division (Walker's corps), succeeding finally in dismantling Alexander's bridge and forcing the Confederates to cross at Lambert's Ford. Polk was to attack Crittenden frontally at Lee and Gordon's Mill after the enveloping force of Forrest, Buckner, W.H.T. Walker, and Bushrod Johnson crossed the creek; the failure of the envelopment meant that Polk could not attack. As a result, Crittenden's corps was not engaged at all during the day.

The First Day (19 September 1863)

       During the night preceding the battle both sides were shifting troops. "Neither army knew the exact position of the other....It is probable that division commanders on either side hardly knew where their own commands were, in the thick woods, let alone the other troops of their own army, or the troops of the hostile army. The lines were at this time about six miles long."
       On the morning of the 19th, Thomas ordered Brannan's division, then posted on the road two miles north of the Lee and Gordon's Mill, to reconnoiter toward Chickamauga Creek. Brannan encountered and drove back Forrest's dismounted cavalry, which called on the nearest Confederate infantry for help. This brought on an all-day battle. Every division of the XIV, XX, and XXI Corps was committed. Of the Confederate forces, only the divisions of Breckinridge and Hindman, on the south flank, were not engaged. Neither side gained any decided advantage.

The Second Day (20 September 1863)

       During the night the two opposing forces further rearranged their dispositions in the difficult terrain. Rosecrans prepared defensive positions, and Bragg planned an attack. Longstreet had arrived during the night; he was given command of the left wing of Bragg's army, and Polk was given command of the other.
       Bragg's units were to attack successively from north to south. Breckinridge attacked on the north at 9 o'clock Sunday morning. Thomas, commanding the Federal left wing, called for Negley's division, which was supposed to be in reserve. Due to an error, however, Negley was in the line. Wood, whose division was in reserve where Negley's was supposed to be, moved up to relieve Negley, while the latter sent one brigade and then another to reinforce Thomas. For two hours, the Federal left had successfully held off heavy attacks.
       Rosecrans' misunderstanding as to the true location of his units then led to a fatal error. He was trying to strengthen the defenses on his right while Thomas held the other flank. Thinking that Wood was on Reynolds' (right) flank, he ordered Wood "to close up and support Reynolds." Actually, Brannan was on Wood's left, and following his instructions, Wood pulled out of the line, passed behind Brannan, and fell in on Reynolds' flank. The divisions of Sheridan and J.C. Davis were closing to fill this gap at abut 11:30 when Longstreet attacked. By a strange coincidence, Longstreet hit the precise point left open by the Federal error. Sheridan's and Davis' divisions were shattered by superior force, and the Federal right was driven back on its left flank.
       Rosecrans, McCook, and Crittenden, unable to rally the troops around them, fled to Chattanooga, thinking the entire army was being destroyed. Thomas remained on the field, turning Wood and Brannan to block Longstreet on the south. Bragg was unable to exploit Longstreet's success. Three brigades of Granger's Reserve Corps ("Army of the Kentucky") were near McAffee's Church with orders to remain there and protect the flank. In a splendid example of battlefield initiative, Granger violated his orders and "at the moment of greatest need reported to Gen. Thomas with two brigades" (Whittaker and Mitchell from Steedman's division). Van Horne says "the opportune aid o these two brigades saved the army from defeat and rout" (Van Horne, I, 353). Thomas held the field until dark and then, on orders from Rosecrans, withdrew to Rossville Gap. Rosecrans withdrew his army into the defenses of Chattanooga. Bragg followed, occupied Missionary Ridge and laid siege to the town.

Epilogue

       Although Bragg had won a decided tactical victory, his piecemeal method of attack and lack of a general reserve deprived him of the success that an outstanding general might have achieved under the circumstances--particularly the rare bit of luck occasioned by Longstreet's attack finding a gap. Failure to pursue the shattered Federals deprived Bragg of the fruits of his victory. The work of Thomas--the "Rock of Chickamauga"--the steadfastness of the troops on his wing, and initiative of Granger, all helped make this a Pyretic victory for the South.
       An evaluation of the statistics shows that the Union had 19.6 percent killed and wounded and Confederates 25.9 percent. Using Livermore's "hit by 1,000" system of comparing the combat effectiveness, Rosecrans' troops killed or wounded 292 Confederates for every 1,000 Federal soldiers engaged; Bragg's forces, on the other hand, killed or wounded 172 Federals for every 1,000 of their own troops engaged. The battle, fought in a densely wooded area which permitted little or no tactical control of units, was one of the bloodiest of the war.
       Chickamauga was a maker and breaker of reputations. Thomas's performance elevated him to top command, and Granger was also marked for higher responsibility. Rosecrans, Alexander McCook, Crittenden, and Negley were relieved: the last three were charged with misconduct but acquitted. The fractious Bragg (who’s personality defect was largely responsible for the poor cooperation of his subordinates) relieved Polk, D.H. Hill, and Hindman for unsatisfactory performance during the campaign.

Source: The Civil War Dictionary, by Mark M. Boatner III