I have been writing about this fort in my War of 1812 blog, but its use continued into the Civil War and beyond.
From Fort Wiki.
This fort was built to protect Portland, Maine.
During the Civil War, stone bastions were erected on the east and west sides of the island with major earthworks connecting them. It was to mount 71 guns, including seven mortars, but the post was never fully armed or garrisoned.
Work continued after the war and modifications were made to mount 10-inch and 15-inch Rodman cannons.
A funding freeze in the 1870s stopped work altogether. By 1903 Fort Scammell was listed as unarmed and not garrisoned.
Two 3-inch anti-aircraft guns were put in place in 1917, but it is not known whether they were ever employed.