US naval forces assisted Grant in the long, complex Vicksburg Campaign, which resulted in Confederate forces surrendering in the Battle of Vicksburg in July 1863, which cemented Union control of the Mississippi River in one of the war's turning points. The one clear Confederate victory in the West was the Battle of Chickamauga. After Rosecrans' successful Tullahoma Campaign, Bragg, reinforced by Lt. Gen. James Longstreet's corps, defeated Rosecrans, despite the defensive stand of Maj. Gen. George Henry Thomas. Rosecrans retreated to Chattanooga, Tennessee, where Bragg was then besieged in the Chattanooga Campaign. Grant marched to the relief of Rosecrans, where he led the defeat of Bragg in the Third Battle of Chattanooga, eventually causing Longstreet to abandon his Knoxville Campaign and driving Confederate forces out of Tennessee and opening a route to Atlanta and the heart of the Confederacy.