The Visitor's Center is pretty small, but packed with exhibits and info. This is a model of a Buoyant Submarine Torpedo, more commonly known as a mine. These were sprinkled in the waters around many American coastal fortifications in the time of the Spanish-American War (1898) and beyond. They were to be detonated remotely via an electric charge, when an attacking ship blundered o'ertop of them. This was the cutting edge of defensive technology at the start of the 20th century, a necessary addition to the dubious defensive utility of the 40-year-old Rodman Guns that still armed the batteries of most US forts.