Compared to the Eastern Theater of the war, Lincoln exercised less direct control over operations that took place West of the Appalachian Mountains. At the end of 1861, Lincoln ordered Don Carlos Buell, commander of the Department of the Ohio, and Henry Halleck, Frémont's replacement as commander of the Department of the Missouri, to coordinate support with Unionists in Kentucky and Eastern Tennessee. General Ulysses S. Grant quickly earned Lincoln's attention, winning the first significant Union victory at the Battle of Fort Henry and earning a national reputation with his victory at the Battle of Fort Donelson. The Confederates were driven from Missouri early in the war as a result of the March 1862 Battle of Pea Ridge. In April 1862, U.S. Naval forces under the command of David Farragut captured the important port city of New Orleans. Grant won further victories at the Battle of Shiloh and the Siege of Vicksburg, which cemented Union control of the Mississippi River and is considered one of the turning points of the war. In October 1863, Lincoln appointed Grant as the commander of the newly-created Division of the Mississippi, giving him command of the Western Theater. Grant and Generals Hooker, George H. Thomas, and William Tecumseh Sherman led the Union to another major victory at the Third Battle of Chattanooga in November, driving Confederate forces out of Tennessee. The capture of Chattanooga left Georgia vulnerable to attack, raising the possibility of a Union march to the Atlantic Ocean, which would divide the Confederacy.