Seavey's Island

Approved by Congress in 1900, a 750-foot (230 m) granite drydock was built in the former gut between Fernald's and Seavey's islands.

After 1815 it was abandoned, then reactivated from 1861 until 1865 during the American Civil War as an 11 gun, 8 inch Rodman naval battery.

Because it projected 540 feet (160 m) into the Piscataqua River channel, Henderson's Point created a navigational hazard for warships visiting the navy yard.

In 1908, the Portsmouth Naval Prison was completed on the southern 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.

The State of New Hampshire brought suit against Maine in the Supreme Court, but the Supreme Court held that New Hampshire was estopped from contesting a previous 1977 boundary determination that Maine had jurisdiction over the island, and dismissed the Complaint.