George Henry Thomas
The Union Army sent reinforcements: Maj. Gen. Joseph Hooker with 15,000 men in two corps from the Army of the Potomac in Virginia and Maj. Gen. William Tecumseh Sherman with 20,000 men from Vicksburg, Mississippi. On October 17, Maj. Gen. Ulysses S. Grant received command of three Western armies, designated the Military Division of the Mississippi; he moved to reinforce Chattanooga and replaced Rosecrans with Maj. Gen. George Henry Thomas.