Fort Moultrie stood at a commanding point on the south end of Sullivan's Island, directly beside Charleston Harbor's main ship channel, the only deep water access to the port, so ships entering the harbor had to pass close under its guns. From the American Revolution through World War II, its position was key to defending Charleston, and the site preserves the evolution of American coastal defense, with traces of nearly all of America's wars in that span as well as the peacetime years between them. During the Civil War, Confederates held the fort, while Union blockade ships and ironclad gunboats kept their distance, Fort Sumter lay partially crumbled from Union bombardment, and enemy ships entering the harbor faced deadly crossfire between Moultrie and Sumter as part of a ring of forts and batteries that made Charleston an unconquerable Confederate stronghold.