This is what's left of the original Upper Water Battery. I believe reenactors periodically uncover the guns and play with them BUT sadly this did not happen while I was there. In 1814 Fort McHenry had Upper and Lower Water Batteries, manned by sailors from the Chesapeake Flotilla. The idea behind the Water Battery concept was that guns along the waterline would "skip" balls into attacking ships' hulls, while cannon on a fort's bastion would decimate ships with plunging fire. All of the original Lower Water Battery was replaced in the 1840's by what is now the Outer Battery.