Seavey's Island side of Seavey's Island at the former site of Camp Long, a stockade named for Secretary of the Navy John Long, where 1,612 prisoners of war from the Battle of Santiago de Cuba were confined from July 11 to mid-September 1898 during the Spanish–American War. Camp Heywood, a Marine camp named after Colonel Charles Heywood, was located just north of the naval prison. It was occupied after the 1st Battalion's return from Cuba in late August until September 21, 1898. According to the National Trust for Historic Preservation, the Portsmouth Naval Shipyard has 62 buildings listed on the National Register
Battle of Santiago de Cuba prisoners were returned to Spain with their “honors of war” on American ships. The battle was the end of any noteworthy Spanish naval presence in the New World. It forced Spain to re-assess its strategy in Cuba and resulted in an ever-tightening blockade of the island. While fighting continued until August, when the Treaty of Paris was signed, all surviving Spanish capital ships were now husbanded to defend their homeland leaving only isolated units of auxiliary vessels to defend the coast. Uncontested U.S. control of the seas around Cuba made resupply of the Spanish garrison impossible and its surrender inevitable.