Located at a high point on the Bagaduce Peninsula, the fort was built as part of an initiative by the British to establish a new colony called New Ireland.

[2] The fort at one time was surrounded by a 20 feet (6.1 m) wall topped with fraising, and with cheval de frise at the base.

[3] Additional defenses included the digging of a canal across much of the neck separating the Bagaduce Peninsula from the rest of the mainland.

Castine is set at a strategically significant location near the head of Penobscot Bay, and was a point of conflict at several times between the 17th and 19th centuries.

Massachusetts, of which Maine was then a part, responded by raising a large militia force, which in an operation known as the Penobscot Expedition, disastrously failed in its attempt to dislodge the British in July and August of 1779.

Upon returning to his home in Camden he was captured, court-martialed and executed by the Americans, tried by Major Benjamin Burton under the direction of Brigadier General Peleg Wadsworth.

[3][13] The state of Maine acquired the fort in 1940, and twenty years later provided funds to rebuild a magazine with other improvements.