Portsmouth Naval Prison

The Portsmouth Naval Prison, sometimes called ‘The Castle’, occupies the southeastern corner of Seavey Island, at Portsmouth Naval Shipyard in Kittery, Maine.

During the Revolutionary War, starting in 1775, Seavey Island was fortified with earthworks and garrisoned by New Hampshire militia to prevent the British Navy from entering Portsmouth harbor. Fort Sullivan, named for General John Sullivan, consisted of several gun batteries facing a similar installation, Fort Washington, on Peirce Island. The opposing cannon of the two forts commanded The Narrows, a constricted stretch of the Piscataqua River between the two islands. Fort Sullivan was again manned during the War of 1812, and it was strengthened for the defense of Portsmouth Navy Yard against Confederate threats during the Civil War. After 1866, Fort Sullivan was dismantled.

Spanish Prisoners Washing Dishes at Fort Long - 1898

During the brief Spanish-American War, a prison encampment known as Fort Long, named for the Secretary of the Navy, John Long, occupied the area of Seavey Island where the Naval Prison stands today. During July of 1898, the Navy transported more than sixteen hundred Spanish prisoners to their temporary home at Fort Long. Their numbers included about a dozen officers and several surgeons and priests. 

To accommodate the mass of prisoners, eight large barracks were erected to house them, eight more were built for their Marine guard, plus six cook houses, three mess halls, and sanitary buildings. To secure the inmates, two Gatling guns, precursors of modern machine guns, were positioned near the camp entrances, and Marines were posted every fifty feet around the perimeter to prevent an escape.

Spanish Prisoners Fishing - 1898

During the summer of 1898, the Spanish prisoners could frequently be seen fishing from the high rocks along the Piscataqua riverbank. Some were paroled and allowed to visit Portsmouth. Their stay on the Seacoast was short-lived, however; the war ended barely a month after they had arrived. 

All of the prisoners, except for thirty who had died from injuries or disease and were buried on the island, were transported to Spain on September 12. The Navy closed Camp Long three years later, in 1901.

Construction of Portsmouth Naval Prison began in 1905, and the first prisoners arrived in 1908. Like Alcatraz Island in San Francisco Bay, it was thought that the fast tidal currents of the Piscataqua River would discourage prisoners from trying to escape, and stop them if they made an attempt. 

The Castle

The prison was enlarged in 1912 by the addition of The Castle, an impressive-looking building with crenelated battlements atop the four guard towers. The roof is made of copper and, like the Statue of Liberty, weathering has caused it to turn green. 

A few years after The Castle was added, the First World War saw an influx of prisoners, until the prison population reached 2,295 inmates in 1918. 

The Fortress

Business was also booming during World War II, requiring two new wings to be constructed: the northeast wing in 1942, and the southwest wing, known as ‘The Fortress’ in 1943. During the final year of the war, 1945, Portsmouth Naval Prison held 3,088 inmates. When Germany surrendered, four captured U-boats were escorted to Portsmouth Naval Shipyard: U-234, U-805, U-873, and U-1228. Their crews were incarcerated and interrogated at the Naval Prison. 


Portsmouth Naval Prison continued to be used through the Korean War and into the Vietnam War years. By 1974, however, it was considered obsolete and closed permanently. It remains vacant to this day. The U.S. government continues to look for someone to lease the facility, although re-use will require a massive cleanup of hazardous materials, especially asbestos.

When it was built, the Portsmouth Naval Prison was considered to be the largest poured-concrete building in the world. In its day, The Castle was the United States Navy’s maximum security prison, and the inmates unlucky enough to be incarcerated here did hard time. A sailor or marine transferred to Portsmouth dreaded the move as much as a civilian sent to Alcatraz. In fact, this infamous brig earned nicknames like ‘The Rock’ and ‘Alcatraz of the East’. Although the prison housed more than eighty-six thousand prisoners during its sixty-six years in service, not one inmate escaped.

The oldest photographs on this page, taken in 1896, were published in C.S. Gurney's 1902 book, Portsmouth . . . Historic and Picturesque. The vintage picture of Portsmouth Naval Prison above is used courtesy of the Library of Congress (LOC) and dates from circa 1912. Mine was taken from a different angle because duplicating the LOC photo would require a boat or trespassing on private property.

The best places to view the Portsmouth Naval Prison are from Peirce Island and from Portsmouth Avenue (Route 1B) near the westernmost tip of New Castle. Due to hazardous materials, and Shipyard security, visiting the closed facility is prohibited.