December 27, an assault force of 150 men seized the Union-occupied Castle Pinckney fortification, in the harbor close to downtown Charleston, capturing 24 guns and mortars, while the small U.S. Army garrison retired to Fort Sumter to join Major Robert Anderson. On December 30, the federal arsenal in Charleston was captured, resulting in the acquisition of more than 22,000 weapons by the militia.

The Confederates promptly made repairs at Fort Moultrie.