Meanwhile, Rosecrans' Army of the Cumberland retreated to Chattanooga after Chickamauga. Bragg pursued and promptly placed the city under siege. On October 17, Rosecrans, who was demoralized, was relieved of command and replaced by Major General George H. Thomas. While Chattanooga was not completely surrounded, Thomas' supply line was very thin. Grant himself arrived at the city of October 23, and expanded the tenuous supply line. After Major General William T. Sherman arrived with reinforcements, the Union troops went on the offensive. A Union victory at the Battle of Lookout Mountain broke part of Bragg's line on November 23. Two days later, Thomas attacked the Confederate line at Missionary Ridge. In the ensuing Battle of Missionary Ridge, the Confederate defenders were completely overrun and the siege was broken. Bledsoe's Battery saw heavy action at Missionary Ridge, suffering a minimum of two casualties; all four of the battery's cannons were captured.