On the first night a large group of patriots led by John Langdon overpowered a six-man caretaker detachment and confiscated much of the fort's supply of gunpowder.

[8] In 1794 the United States Army took over the fort as part of the first system of US fortifications, adding a two-story blockhouse.

[11] As recommended by the Endicott Board of 1885, construction began in 1898 on three forts to defend the Portsmouth area.

[18] An underwater minefield also guarded the harbor, initially controlled from a mine casemate at Fort Stark.

Camp Langdon (named for the Revolutionary War hero and originally the New Military Reservation) was established in New Castle due to insufficient space at the forts.

[27] References indicate the authorized strength of CD Portsmouth was 10 companies, including four from the New Hampshire National Guard.

Though most of the regiment was in the Harbor Defenses of Portland (Maine), the 8th Coast Artillery was also the Regular Army component of HD Portsmouth from 1 July 1924 through early 1940, when the new 22nd Coast Artillery assumed that duty; there does not appear to have been a National Guard harbor defense regiment in the area.

[27] Early in World War II numerous temporary buildings were again constructed to accommodate the rapid mobilization of men and equipment.

Fort Dearborn was built in the town of Rye from April 1942 to September 1944, its main armament being Battery Seaman (a.k.a.

[26] An unusual combined Army-Navy harbor entrance control post/harbor defense command post was built atop the disarmed 6-inch battery at Fort Stark; it was designed to resemble a modern luxury beach cottage.

[20] With greatly reduced manpower requirements, the 22nd Coast Artillery was dissolved on 1 March 1944, with some personnel reassigned to HD Portsmouth.

The remaining elements were moved to Camp Hood, Texas for inactivation by reassigning their personnel to five field artillery battalions.

[18][30] The battery was initially part of the Harbor Defenses of Boston, but was transferred to HD Portsmouth with the construction of a fire control station for Fort Dearborn.

[31][32] Numerous fire control towers and other structures were built from Kennebunkport, Maine to Cape Ann, Massachusetts to support HD Portsmouth, particularly the 16-inch guns at Fort Dearborn.

Most of the other batteries are fenced off, or with interior access otherwise impeded, but are visible and reasonably free of overgrowth.

Most of the fort is intact as rebuilt in 1808 (except the demolished north front); the incomplete third system walls remain; the Endicott 8-inch batteries are fenced off but visible.

Fort McClary's blockhouse is well-preserved and interpreted; remnants of the abortive third system additions can be seen, including large piles of granite blocks, a mostly-complete bastion, and a small caponier in the seawall.

[13][14] Fort Stark has a small museum in an outbuilding, the unusual harbor entrance post, and well-preserved batteries.

Fort Foster Park has a public beach, a rare World War II mine casemate with air conditioning on top, and two fire control towers.