Fort Slocum was built by the 2nd Rhode Island Infantry. The fort had 25 guns and mortars, and commanded the intersection of the left and right forks of Rock Creek Church Road (near today's New Hampshire Avenue and McDonald Place). The fort also provided support for Fort Stevens to the west.
Fort Slocum was named after Colonel John Slocum of the 2nd Rhode Island Infantry. Colonel Slocum was killed on July 21, 1861 at the First Battle of Manassas (also known as the First Battle of Bull Run).