From the last days of September through October 1863, Gen. Braxton Bragg's army laid siege to the Union army under Maj. Gen. William Rosecrans at Chattanooga, cutting off its supplies. On October 17, Maj. Gen. Ulysses S. Grant received command of the Western armies; he moved to reinforce Chattanooga and replaced Rosecrans with Maj. Gen. George Thomas. A new supply line was soon established. Maj. Gen. William T. Sherman arrived with his four divisions in mid-November, and the Federals began offensive operations. On November 23-24, Union forces struck out and captured Orchard Knob and Lookout Mountain. On November 25, Union soldiers assaulted and carried the seemingly impregnable Confederate position on Missionary Ridge. One of the Confederacy's two major armies was routed. The Federals held Chattanooga, the "Gateway to the Lower South," which became the supply and logistics base for Sherman's 1864 Atlanta Campaign.