SEPTEMBER 21SECOND DAY. General Bragg issued orders to his subordinates to resume the battle at daybreak. On the Confederate right Breckinridge's Division was to begin the attack which would be taken up by successive divisions to the left. Sunday morning came. Daylight began to creep over the battlefield. The sun rose, but no attack came. Bragg waited impatiently. Finally, the orders reached Hill at 7:30 a. m. Further delay followed as the troops moved into position. About 9:30 a. m. Breckinridge advanced to attack, followed by Cleburne. The extreme left of the Union line fell back, but the fire from the Union breastworks halted further Confederate advance. Reinforcements hurried to Thomas. In further fighting at this part of the line neither side made any considerable gain, as Rosecrans sought to hold his left against Polk's furious attacks. Almost equally matched, neither Thomas nor Polk could show any appreciable gains throughout the morning. About 11 o'clock a lull occurred as Longstreet's wing prepared to move against the center in Bragg's plan of attack.
The Union center at which Longstreet pointed his attack was held by Brig. Gen. Thomas J. Wood's Division which had replaced Negley's Division in the line when the latter had reinforced Thomas early in the morning. To the immediate left of Wood were the troops of Brannan's Division, and on Brannan's left, Maj. Gen. Joseph J. Reynolds' Division.
An hour before noon as the Confederate right wing poised to strike, an irreparable blunder occurred on the Union side. A staff officer riding from Thomas' headquarters near Kelly Field reported to Rosecrans that he had noticed Brannan's Division was out of line and believed "General Reynolds' right was exposed." Rosecrans, without further investigation, immediately ordered Wood to "close up on Reynolds as fast as possible and support him." In order to do this, Wood had to pull his division out of line and march behind Brannan's Division toward Reynolds. Wood's division had left its place in the line, creating a true gap where none had actually existed before, and had started to march northward behind Brannan when Longstreet's column of five divisions accidentally struck into the gap.
Longstreet's attack hit Wood's and Brannan's Divisions on their exposed flank and drove them from the immediate field of battle. On the other side of the gap the Confederates struck Brig. Gen. Jefferson C. Davis' Division, which was marching up to take Wood's place in the line, and Maj. Gen. Philip H. Sheridan's Division in flank. In a very short time the entire Union right flank was in disorder and driven from the field. Wilder's brigade on the extreme right made a valiant stand for a while, employing to good effect the heavy fire power of the Spencer repeating carbine with which it was armed. Nothing, however, seemed to daunt the onrush of the Confederates, and Wilder withdrew for fear of being cut off from escape.
The routed divisions from the Union right withdrew northwestward through McFarland's Gap to Rossville. Generals Rosecrans, Crittenden, and McCook were caught in the breakthrough and fled the field. General Thomas was now in command of the Union forces left there.
The altered conditions of the battlefield now dictated a change in Confederate strategy. The original plan of enveloping the Union left changed to a sweep from the Union right to the left. A pause in the fighting enabled Thomas to form a new line quickly to his rear on Snodgrass Hill, almost at a right angle with the Union left. From this vantage point he met the onslaught of Longstreet's troops with such stubborn and determined resistance on that Sunday afternoon that he earned the name "Rock of Chickamauga."
The Union line on Snodgrass Hill was composed of Brannan's Division with fragments of Wood's, Negley's and Van Cleve's Divisions. Longstreet vigorously assaulted the line again and again and nearly succeeded in enveloping Brannan's right. Confederate success seemed assured as Thomas' troops were hard hit and were short of ammunition, but at this moment unexpected reinforcements reached General Thomas.
General Granger, without orders and following the sound of battle, had hastened to the aid of Thomas. He arrived at Snodgrass Hill at a very opportune moment and just in time to stop the Confederates from enveloping Brannan's right. A fierce engagement took place as Brig. Gen. James B. Steedman's Division of Granger's Corps forced the southern troops from the crest of the hill.
Midafternoon found Longstreet once again attempting to wrest the hill from Thomas' troops, using McLaw's, Hindman's, and Bushrod Johnson's Divisions, and again he was repulsed. Later in the afternoon, Longstreet asked Bragg for reinforcements but was told none were available and that the right wing "had been beaten back so badly that they could be of no service" to him. Longstreet determined to make one more effort. He formed a column of such troops as were available and again assaulted the hill. The fight was desperate and lasted until nightfall. The Union troops repulsed some of the Confederate charges with the bayonet as their ammunition was nearly exhausted. Finally, Longstreet pushed Steedman back to the next ridge and occupied the ground to the right of Brannan.
The left of the Union line around Kelly Field spent a relatively quiet afternoon compared to their comrades on Snodgrass Hill. However, a bout 4 p. m., the divisions of Hill's corps and part of Walker's again assaulted the Union positions there. By 6 p. m., Cheatham's Division had joined the attack. This attack succeeded in enveloping the Union left, and the road to Rossville, through Rossville Gap, was cut off for the moment.
In the meantime, Thomas received orders from Rosecrans to "Assume command of all the forces, and with Crittenden and McCook take a strong position and assume a threatening attitude at Rossville." Although Thomas received these orders with little delay, it was late afternoon before he sent instructions to Reynolds to begin the withdrawal and move into position to cover the retirement of the other troops on the left. In executing this movement, Reynolds was forced to drive off the Confederate troops who had begun to envelop the Union left. The Union army withdrew in relatively good order. The troops holding Kelly Field moved out first, followed by those who had stubbornly resisted Longstreet's attacks upon Snodgrass Hill.
While the retreat from the battlelines may have been in "good order," General Beatty's description of the march to Rossville amply describes the scene: "The march to Rossville was a melancholy one. All along the road, for miles, wounded men were lying. They had crawled or hobbled slowly away from the fury of the battle, become exhausted, and lain down by the roadside to die." Beatty reached Rossville between "ten and eleven" and reported, "At this hour of the night (eleven to twelve o'clock) the army is simply a mob. There appears to be neither organization nor discipline. The various commands are mixed up in what seems to be inextricable confusion."
Nevertheless, Thomas placed his forces at Rossville Gap and along Missionary Ridge in preparation against further attacks. The morning of the 21st found the Union Army of the Cumberland more or less reorganized. With the exception of some skirmishing, the Union forces were not molested.
The losses on both sides were appalling and the percentages surprisingly equal. The following tabulation of casualties at the Battle of Chickamauga is based on Thomas L. Livermore's Numbers and Losses in the Civil War in America, 186165: