Down the hill to Fort Griswold's southwest is a Water Battery, to which I have seen referred as both the Lower Battery and River Battery. Whatever one calls it, it's a battery of guns intended to fire at attacking ships from as close to water level as possible, while the guns in the fort fired from above.

The Lower Battery is the one part of Fort Griswold that was modernized as time marched on, while the main fort retained its shape and character, likely by dint of its holy Revolutionary War performance.