The Siege of Port Hudson occurred from May 22 to July 9, 1863, when Union Army troops assaulted and then surrounded the Mississippi River town of Port Hudson, Louisiana, during the American Civil War. In cooperation with Maj. Gen. Ulysses S. Grant's offensive against Vicksburg, Mississippi, Union Maj. Gen. Nathaniel P. Banks's army moved against the Confederate stronghold at Port Hudson. On May 27, 1863, after their frontal assaults were repulsed, the Federals settled into a siege that lasted for 48 days. Banks renewed his assaults on June 14 but the defenders successfully repelled them. On July 9, 1863, after hearing of the fall of Vicksburg, the Confederate garrison of Port Hudson surrendered, opening the Mississippi River to Union navigation from its source to the Gulf of Mexico.