As are all casemated American seacoast defenses built in the first half of the 19th century, Fort Wool's firing embrasures are blessed with the remains of Totten Shutters. These were swinging iron doors designed to protect gun crews from small arms fire while they reloaded their piece, and what we see at the bottom of this embrasure are the holes into which spring-loaded bolts would automatically lock the doors shut after each discharge of the gun. Don't forget to unlock those doors before firing again, gun crew!