At the outbreak of the American Civil War, several pro-Union areas found themselves isolated in Confederate states. The two most significant of those areas were west Virginia and east Tennessee. West Virginia was easily accessible from the North, and successfully seceded from the Confederacy, with Federal military support. In contrast, east Tennessee was isolated behind the Cumberland Mountains. The only railroad through the area connected south west Virginia with northern Georgia, two staunchly Confederate areas. Despite this isolation, President Lincoln was determined to occupy the area. Every commander in Kentucky and Tennessee was constantly being reminded of this. One attempt in the winter of 1862 had been beaten by the mountain weather. An attempt to invade from the north had been defeated by Thomas Jackson (Battle of McDowell, 8 May 1862).
The first half of 1862 had seen the Confederacy thrown out of western Tennessee. After victory at Shiloh (6-7 April 1862) and the fall of the Confederate strong point of Corinth (25 May), a strong Union army under Don Carlos Buell had been sent towards eastern Tennessee, with the aim of capturing Chattanooga. Buell had moved so slowly that Braxton Bragg, commanding the Army of Tennessee had been able to prepare and launch an invasion of eastern Kentucky. This invasion had been defeated by a concentration of Union forces, culminating in a drawn battle at Perryville (8 October 1862) after which Bragg had realised how many Union soldiers he faced and pulled back to Murfreesboro in central Tennessee, from where he was forced to pull back after the Battle of Stones River or Murfreesboro (31 December 1862 to 1 January 1863).
Two Tennessee campaigns were planned for 1863. General Rosecrans was to launch an attack on Chattanooga from his position at Murfreesboro, where he had remained after the battle. Meanwhile, a smaller force under General Burnside was to cross the mountains from Lexington, Kentucky into East Tennessee and threaten Knoxville. Together these moves would cut a major railroad from Virginia to Georgia and secure a Unionist area.
When Burnside's expedition was planned, a Confederate army some 14,000 strong under General Simon Bolivar Buckner was present in the upper Tennessee River, centred on Knoxville. Burnside left his Kentucky base on 4 August with 12,000 men. He was well aware that he would be outnumbered at Knoxville, and so when his ninth corps returned from Vicksburg, Burnside used them to replace garrison troops and increased his field army up to 15,000. During the second half of August that army moved through several different passes through the Cumberland Mountains, before combining at Kingston, forty miles west of Knoxville, on 1 September.
By now Buckner had been withdrawn to join Bragg at Chattanooga. A rearguard had been left at Loudon, on the south bank of the Tennessee River. This was where the railroad from Knoxville to Chattanooga crossed the Tennessee. On 2 September Burnside sent a detachment towards Loudon. As they approached the Confederate rearguard burnt the railway bridge then withdrew.
The next day Burnside's men entered Knoxville. They were greeted as heroes, partly because some of his units were made up of men from East Tennessee who had crossed over into Kentucky to volunteer. He didn't stay for long. A Confederate force 2,500 strong under Brigadier-General John W. Frazer had been left guarding the Cumberland Lap on the north eastern border of the state. Burnside moved north to deal with this force and open a more direct route to Kentucky. On 9 September Frazer surrendered to Burnside's much larger force.
On 10 September Burnside received news of the capture of Chattanooga. Everything looked to be going well, so he spent the next week organising new units of Tennessee volunteers. The only immediate threat came from Major-General Samuel Jones, commander of the Confederate forces in south-west Virginia, 150 miles to the north east. Burnside decided to concentrate against this force to secure his flanks before moving to help Rosecrans.
This campaign coincided with the arrival of orders from Washington. Burnside's infantry was ordered south to Chattanooga to support Rosecrans. This was part of a general concentration ordered when it was clear that Rosecrans was in some danger. Burnside could not abandon his campaign against Jones. Over five days (18-22 September), he hit Jones on both flanks, then concentrated in front of the main Confederate position at Carter's Station, where there was a key railroad bridge. Expecting a federal attack, Jones burnt the railroad bridge over the Watauga River then retreated back towards Virginia.
This allowed Burnside to start moving most of his men back towards Chattanooga. Two infantry regiments and a brigade of cavalry were left at Bull's Gap, about halfway along the railroad between Knoxville and the Virginia border. By the end of September most of his men were between Knoxville and Loudon. On 18 September a cavalry battalion had reached as far south as Cleveland, almost within touching distance of Rosecrans at Chattanooga, but his defeat at the battle of Chickamauga (19-20 September) meant that this force was dangerously exposed, and Burnside pulled his most advanced troops back to Sweetwater, about half way between Cleveland and Knoxville.
From his new position Burnside sent a series of suggestions of ways he could help Rosecrans back to Washington, but the immediate panic was already over. Bragg had settled down to besiege Chattanooga, and strong Federal reinforcements were rushing to the vicinity along Union controlled railroads. Burnside was now ordered to hold his position and to be ready to respond if Rosecrans called for help.
The first threat came not from Bragg but from Jones in Virginia. The small forces left behind at Bull's Gap were not strong enough to deal with this new Confederate expedition, and so Burnside led a large part of his army back up the Loudon valley. On 10 October he won a minor battle at Blue Springs, pushing Jones back into Virginia. He was even able to briefly cross over into that state to destroy more of the railroad.
The success or failure of Burnside's expedition was firmly tied to the progress of events around Chattanooga. Two of those events combined to increase his vulnerability. First, Bragg had fallen out with his subordinates (again!). President Davis had traveled to Bragg's camp at Chattanooga to try and sort out this mess, and while there had suggested that Longstreet's corps, sent from Virginia to reinforce Bragg just in time to participate at Chickamauga, should be sent up the Tennessee valley to recapture Knoxville. This suggestion had not been immediately carried out, but on 23 October General Grant arrived at Chattanooga to take command, and within a week he had created the 'cracker line', a new supply route into Chattanooga that ended Confederate hopes of starving out the defenders.
Bragg had already moved one division north. On 22 October that division had pushed the Federal troops out of Sweetwater and Philadelphia. On 4 November Bragg finally sent Longstreet's corps to attack Knoxville. Longstreet took 10,000 infantry and 5,000 cavalry from Chattanooga to join the 5,000 men already in the area, giving him a probable force of 20,000 men. When the siege eventually began, Burnside could oppose him with 12,000.
Bragg's plan was for Longstreet to move quickly against Burnside, capture Knoxville and return to Chattanooga before Grant could launch his attack. Unfortunately it took a week for Longstreet to reach Sweetwater. He eventually crossed the Tennessee River at Loudon on 14 November. Over the next few days the two armies fought a running battle back along the Tennessee to Knoxville. On 16 November they came close to a full scale battle at Campbell's Station, but Burnside was able to withdraw. The bulk of his army entered the defences of Knoxville on 17 November.
Those defences had been begun by the Confederates. Soon after reaching Knoxville Burnside had ordered the defences improved, but not with a major siege in mind. On 17 November the defences were not ready to withstand a serious attack. While the infantry worked on improving the defences, a cavalry division under Brigadier General W. P. Sanders found a desperate delaying action. They managed to hold back a Confederate attack on 18 November until about 2.30 in the afternoon, when Sanders was killed. With the death of their commander the division finally broke, but it had done its job - the defences of Knoxville were complete.
Longstreet began his formal siege on 19 November. The next day he began to dig attacking trenches, approaching the Federal lines. However, Burnside's biggest problem was food. His supply lines had always been tenuous, stretching back to Kentucky over mountain roads. On 23 November he managed to get a telegraph out to Grant reporting that he had ten to twelve days of supplies, and could hold out for that long but would then have to surrender or retreat. This information played heavily on Grant's mind and played a part in deciding the date of his attacks on Lookout Mountain and Missionary Ridge.
In the end the supply situation was partially solved by the local loyalists. They gathered food and supplies upriver from Knoxville and floated them down to the besieged garrison, who strung a barrier out across the river to catch them. When Sherman's relief column eventually arrived, Burnside had more supplies in hand than when he had sent his telegraph.
Longstreet was well aware that his time at Knoxville was short. Events at Chattanooga could cut him off at any time and force him to abandon the siege. Accordingly, he began planning for an assault as soon as he had examined the new defences.
Both sides agreed on the most vulnerable part of the defences. At the north west corner of the defences was Fort Sanders, built on the same site as a earlier Confederate fortification. This had not been designed to be part of a continuous line of fortifications and bulged out of the line.
Longstreet first planned to attack on 25 November. However, on 24 November Longstreet learnt that another 2,600 men were on their way, so he postponed the attack. When those troops arrived, they were accompanied by General Leadbetter, Bragg's chief engineer, who had been posted at Knoxville when it was in Confederate hands. The attack was delayed again so that he could examine the new defences. These were precious days. 25 November had seen Bragg forced off Missionary Ridge. Union forces from Chattanooga would soon be rushing towards Knoxville. Every day also saw the Federal defences improve
Fort Sanders was very nearly a typical earthwork fort. It was built on a hill to the west of Knoxville. The outermost defences were provided by a line of rifle pits, about 150 yards from the fort, used by the Union pickets. The slope of the hill was covered with tree stumps, between which wire had been stretched (not barbed wire - that was not invented until after the war). The fort itself consisted of a ditch and rampart. The ditch varied from four and a half to ten feet in depth, depending on the terrain. The rampart rose behind the ditch at an angle of about 45 degree. This type of angled earthwork was designed to resist artillery fire. Normally there would be a flat space between the edge of the ditch and the start of the wall. Known as a berme, this was designed to prevent the weight of the walls making them to fall into the ditch. However, the berme was a great help to any attacking force, providing a good foothold on the edge of the walls, and so General Orlando Poe, the chief engineer of the defences, had sliced away the berme in preparation for the assault.
The original plan had been for a proper artillery bombardment followed by a full assault. However on Saturday 28 November Longstreet changed his mind, and ordered a surprise attack by the infantry just before dawn. The aim was to rush the Federal lines before the defenders were fully alert to the danger. With this in mind, it is not entirely clear why Longstreet ordered his skirmishers to capture the rifle pits in front of the fort late on the evening of 28 November.
Behind that line of rifle pits, three brigades of infantry were waiting to launch their attack with a fourth ready in support. Like most units on both sides, by 1863 these brigades were far below their theoretical strength, averaging at about 1,000 men each. Inside the fort itself were500 Union soldiers, but another 1,000 were in positions to the left and right of the fort from where they could contribute.
The attack was launched at first light on 29 November. The wire entanglements didn't slow the attack much, but did play a part in disrupting its organisation. The three brigades soon merged into one mass of men, which soon reached the north west corner of the fort. There the fighting developed into a stalemate. The Confederate attackers were able to lay down a covering fire that prevented the Union defenders from firing over the parapet, but were themselves unable to make any more progress.
Some men jumped down into the ditch and attempted to climb the walls. However, the lack of a berme and the icy ground combined to make it almost impossible for a significant number of men to reach the parapet, and those who did were almost immediately shot by the defenders. Several times Confederate flags were planted on the parapet, a gesture meant to encourage the rest of the unit to rally around their flag, but here the flag bearers were nearly all killed and the flags captured. One or two Confederate soldiers did manage to get into the fort through gun embrasures but again not in enough numbers to achieve anything.
Although the Union troops directly in front of the attack were pinned down, there was enough flanking fire to make life in the trench very uncomfortable. After about twenty minutes it became clear that the attack had failed. Those Confederate soldiers who had not entered the ditch were forced to retreat. The survivors in the ditch soon surrendered. Meanwhile, the support brigade also launched its attack, despite efforts by Longstreet to prevent it, and was also repelled.
Confederate losses in the attack had been very heavy. Of roughly 4,000 men engaged in the attack, over 800 were casualties (129 killed, 458 wound and 226 captured - the nature of the fighting prevented there being any missing). Federal losses were around 20.
After the repulse on 29 November, Longstreet began to plan for another assault, but news of Bragg's defeat on Missionary Ridge arrived before it could be launched. Bragg's first orders were for Longstreet to move south to rejoin Bragg's army. On 1st and 2nd December the Federal defenders of Knoxville saw the first signs of preparation for a withdrawal.
The Battle of Missionary Ridge (25 November 1863) had seen Bragg's army pushed decisively away from Chattanooga with heavy losses. This allowed Grant to detach Sherman towards Knoxville on 29 November with a strong relief force (his own corps as well as a smaller force under General Granger that had been making slow progress). During his advance Sherman made every effort to make sure that Longstreet knew he was on his way. The last news from Knoxville to reach Grant had suggested that Burnside was close to being force to surrender by lack of food. Sherman's main concern was thus to force Longstreet away before that happened rather than any desire to force a battle. He need not have worried. The supply situation inside Knoxville had improved rather than worsened - the long-believed-in Unionist population of East Tennessee did indeed exist, and food was floated down the river into the town.
In fact Bragg had informed Longstreet of Sherman's movement almost as soon as it had begun and had cancelled the orders to move south. Instead it was decided that Longstreet should stay at Knoxville as long as possible in order to prevent Sherman from returned to the pursuit of Bragg. The Confederate force finally left Knoxville on the night of 4 December, on an overnight march of eighteen miles that took them to Blain's Cross-roads. After a sharp fight at Bean's Station (14 December), they eventually ended up in the north eastern tip of Tennessee, where they remained over the winter of 1863-4, before rejoining the Army of Northern Virginia on 22 April 1864, just in time for the Battle of the Wilderness.
They were allowed to over-winter without too much interference from Union forces. At least six different generals had command of the operations against him over the winter. Sherman soon returned to Chattanooga leaving Burnside back in command. Burnside was replaced by General Foster who was unwell and delegated the command to General Parke, who passed the command to General Granger, the commander of the original relief force. He in turn passed command at the front to General Sheridan, who was himself ordered away at the end of December.
Not that it really mattered. With the danger to Knoxville over the important Unionist area of East Tennessee was finally secure. The removal of 10,000 infantry, 5,000 cavalry and one of the most able corps commanders from Bragg's army besieging Chattanooga had greatly weakened it, making it much more vulnerable to Grant's counterattacks. With Tennessee lost, the focus of the war in the west was about to shift from the border states to Atlanta and the heart of the Confederacy.