John G. Nicolay, The Outbreak of Rebellion

[63] shallows nearly midway at the entrance of Charleston harbor. It was a five-sided structure, about three hundred by three hundred and fifty feet in size; its walls were some eight feet thick and forty feet high. It was capable of mounting one hundred and forty guns, two tiers in casemates and one behind the parapet. When Anderson took possession of it the preceding Christmas, the casemates were in an unfinished condition, and only a few guns were mounted. Captain Foster, the accomplished engineer of the fort, had, however, since then, by the many expedients known to military science, and by help of a considerable force of workmen and laborers, pushed its defences forward to a state of relative completeness, even with the limited means and materials within the fort. Most of the embrasures of the lower tier of casemates were closed. A total armament of forty-eight guns was ready for use. Of these twenty-one were in the casemates, and twenty-seven on the rampart, en barbette. The garrison consisted of nine commissioned officers, sixty-eight non-commissioned officers and privates, eight musicians, and forty-three non-combatant workmen, to whom, during the last ten days, the besiegers had refused permission to depart, in order that they might help consume Anderson's small stock of provisions, and thus hasten the process of reducing the fort by starvation.

The rebels had built their siege-works on the approaching points of the islands forming the harbor. These lay in a sort of triangle about the fort: Sullivan's Island, containing Fort Moultrie, to the northeast at a distance of 1,800 yards; Cumming's Point, on Morris Island, to the south at a distance of 1,300 yards; and on James Island, near old Fort Johnson, to the west at a distance of 2,500 yards. Their total armament embraced forty-seven guns.

Thus, in numbers, the armaments appeared about equal,