The Union forces were able to hold off Confederate assaults on their fortifications in Chattanooga, which lay on the southern side of the Tennessee River, so Bragg ordered a siege. While Rosecrans's men hunkered down in the city, Bragg's men took up positions in the hills outside, notably on Missionary Ridge and Lookout Mountain, their lines of trenches and fortifications touching the river both upstream and downstream of the town. By early October Confederate artillery commanded the routes by which supplies could be brought into Chattanooga. Within weeks, the entrenched Union soldiers found themselves perilously low on food and other supplies.
While preparing his battle plans, Grant reconnoitered some of the front lines. Rebel soldiers recognized him, marched out, and gave him a formal salute. Grant also had a brief talk with a Confederate private who had come to a stream to fetch water.
The North responded by placing Grant in command of the military district of the west, and thus in command of the army in Chattanooga. Grant headed for the city to help relieve it and defeat the besieging Rebels. One of his first acts was to replace Rosecrans with Thomas. Then, with his chief engineer, William F. Smith, he developed a daring plan to break the Confederate siege. The first part of his strategy was to open a supply line across a long loop in the Tennessee River by driving away Confederate forces there. Once done, supplies could be brought in by boat, wagon, and bridge.
Grant was able to do this and put his so-called “cracker line operation” into effect on October 26. The first supply ship arrived safely on November 1. As he waited for reinforcements to arrive from Memphis and Vicksburg, Grant planned the next step of his offensive: forcing the Confederates off their dangerous position on Missionary Ridge and from Lookout Mountain.
At the same time that Grant was forming his strategy, the Confederate army underwent some dramatic changes. Generals Leonidas Polk, Daniel H. Hill, and Thomas C. Hindman, disgusted with Bragg's slowness at Chattanooga, complained to the War Department and were granted transfers. Bragg also picked this time to send several divisions and thirty-five cannon under the command of Longstreet eastward against Burnside in Knoxville. This move severely weakened Bragg's lines on Missionary Ridge just as the Union army was getting ready for a major assault.