Today is the 150th anniversary of the end of the Battle of Chattanooga. The Chattanooga campaign lasted a while - the situation developed after Chickamauga: the Union army was defeated, retreated to Chattanooga, to the city itself - the Confederates followed, and occupied the high ground around the city, blocking most of the easy resupply routes. For a month or so they tried to starve the Yankees out - then Grant arrived, and set in motion a plan to get supplies through.
That was an interesting campaign itself - a night crossing of the Tennessee river, to allow the men of the Army of the CUmberland (George Thomas' army, which had been holding Chattanooga) to link with men from the Army of the Potomac, who had been brought west under Fightin' Joe Hooker. It all worked - the forces united, repulsed a night attack by the Confederates, and were able to open a short and reliable supply line, to feed the troops in Chattanooga. All that happened in late October - Grant then went to work on a plan to drive off the rebels holding the high ground (Lookout Mountain and Missionary Ridge), a plan that depended on the arrival of Sherman's army of the Tennessee. While that was happening, the Confederates feuded and divided their forces (Bragg sent Longstreet's corps off to Knoxville to harass Ambrose Burnside), thus leaving themselves badly outnumbered by the time the fighting started. They did very little to improve their positions - they were almost as badly supplied as the Army of the Cumberland. They held ground that looked very formidable, but had done all they could to neutralize their advantages.
When all was ready, Grant expected to put the burden of the fighting on Sherman's army. Their part in the plan was to cross the Tennessee on the Union left, and attack the Confederate right, at the end of Missionary Ridge. Thomas' army was not expected to do much - they had been shot to pieces at Chickamauga, and on short rations since, and were not considered ready for much fighting. Hooker's men, on the Union right, were mostly charged with pinning down what rebels they could, to keep the Confederates from shifting men to oppose Sherman. But all these plans started to come apart.
First - Hooker's men attacked Lookout Mountain, a high, rough mountain at the left end of the Confederate line - they went up the side of the mountain, managed to break the rebel lines in a couple places, and ended up taking it. It was a rather remarkable feet - a high, wild mountain, topped with nearly sheer cliffs - but the terrain tended to break up regular formations, and the union was able to negate the South's advantages there. By the end of November 24, the rebels had abandoned the mountain, leaving Hooker in possession.
On the 25th, the plan was for Sherman to attack to the other end of the Confederate line, while Hooker looked threatening, and Thomas waiting. But this went wrong. Sherman had some bad information - the hills were broken and ragged on that part of the field, and he found that he had not taken the position he thought - when he started attacking, he found himself facing another line of hills. He delayed badly allowing the Rebels to reinforce and prepare, and attacked in an uncoordinated and inefficient way, and made no progress. That threw the whole plan off balance - but then, the Army of the Cumberland attacked.
They were not expected to take an active part in the fighting. They were worn down from their experiences - and Grant didn't exactly trust the army or Thomas. They were also lined up in the valley, under Missionary Ridge - commanding high ground where the Rebels had been entrenched for some time. But as things went badly for Sherman, Grant decided to order Thomas' men forward. Not really expecting to accomplish a lot - but hoping that the Confederates would be forced to shift men away from Sherman's front. So - Thomas' army was ordered to attack the Rebel positions at the bottom of Missionary Ridge - and they took the whole thing. It was an odd, somewhat botched attack - the orders were vague - some commanders through they were supposed to take the lines at the bottom of the ridge only; others thought they were expected to go as far as they could. No one quite looked at it as anything more than a diversion. But it worked.
As it happened - the rebel lines were deceptive. The ground looked strong, their entrenchments looked strong - but the lines were poorly laid out, with little mutual support, especially given the steep hillside. The lines were held by far too few men - who were divided between the bottom and top of the ridge. On the other side - the initial attack succeeded, giving the Union control of the lines at the bottom of the ridge - but there, they were exposed to murderous fire from higher up - many of them had no choice but to continue up the ridge. So up they were - they reached the top - they broke the lines there - and swept all of Missionary Ridge clear.
It was a heady day of rate Army of the Cumberland - humiliated at Chickamauga, treated as distinctly second (even third) best by Grant (and Sherman and Hooker), they had come into the battle, almost by accident, after Sherman's failure and carried the day. They had their vengeance. They proved their worth. They made George Thomas' career (though he had little to do with any of it - he argued against the attack, did very little to control it), as well as adding another triumph to Grant's career (though he didn't have much to do with it either: the Cracker Line campaign was really George Thomas and Baldy Smith; Hooker's success at Lookout Mountain came against Grant's directions; Sherman's attack had failed; this one was supposed to be a glorified demonstration.) The battle also elevated Philip Sheridan, one of Thomas' division commanders - he would go east with Grant, command the cavalry, then an army, and be instrumental in winning the war. He was very prominent during the storming of Missionary Ridge, riding around making himself conspicuous - the sort of thing that gets attention, though his general air of aggression wasn't just for show.
And so it was. Bragg's army was routed. Bragg himself would finally be relieved after this, Joe Johnston put n charge, sometime over the winter. The Union held Chattanooga, once and for all - a perfect starting point for their innovation of George in the spring.