The bomb-proof headquarters at Fort Sewall, covered with several feet of earth, consisted of four rooms from left to right: Room A, a kitchen with a fireplace and well; Rooms B and C, guard rooms for officers on duty; and Room D, a small windowless dungeon entered from Room C where a few British or French prisoners were held briefly. At the rear of Room C, a curved brick stairway led to the upper level and the magazine entrance, and two underground ammunition magazines lay below the upper level.