Fort Moultrie
Fort Moultrie and Fort Sumter controlled Charleston Harbor.
Fort Moultrie, on Sullivan's Island directly in front of you, had been an early harbor defense and was the site of Charleston's famous Revolutionary War palmetto-log fort. Fort Sumter was built here on a shoal opposite Fort Moultrie when America strengthened its seacoast defenses after the War of 1812. Charleston's narrow main ship channel passed between the two forts. Enemy ships venturing there would be trapped in a crossfire of cannon.
With the surrender of Fort Sumter in 1861, Union forces evacuated, leaving Charleston's defenses in Confederate hands. The South effectively controlled the harbor from 1861-65 despite Union blockade and bombardment, and the port of Charleston remained open to daring blockade runners supplying the South.
Courtesy hmdb.org