Following the disastrous defeat at Chickamauga, Union forces were in disarray and the tactically vital Chattanooga was under siege and on the brink of falling. Secretary of War Edwin Stanton ordered Ulysses Grant to send the Army of the Tennessee to reinforce Chattanooga. Grant had already reacted. The situation was dire. It required outstanding leadership to rescue the Union position. President Abraham Lincoln decided Grant was the man for the occasion. In early October, Grant was promoted to command of the Military District of Mississippi and told to clean up the mess created by Chickamauga. With those orders, a new undertaking began: the Chattanooga Campaign. This book tracks how, over the next three months, Grant would orchestrate the movements of three Union Armies—the Army of the Cumberland, the Army of the Tennessee, and two Corps from the Army of the Potomac—ultimately leading them into a series of battles that saw them break the siege of Chattanooga. In three battles conducted over the course of three days, the Union forces broke the Confederate army entrenched in the heights overlooking Chattanooga.