St. Louis' Benton Barracks became the mustering depot for western troops, and in February 1862, Department of Missouri commander Henry Halleck approved a joint invasion of west Tennessee along the Tennessee and Cumberland Rivers. Army troops under Brigadier General Ulysses S. Grant, alongside the newly built Western Gunboat Flotilla commanded by Navy Flag Officer Andrew Hull Foote, captured Fort Henry and Fort Donelson, unhinging the Confederate defensive perimeter in the west. After the subsequent Battle of Shiloh, the Federal Army pushed into northern Mississippi, while the Gunboat fleet moved down the Mississippi with cooperating Federal troops, systematically capturing every Confederate position north of Vicksburg, Mississippi.