It lay opposite New Brunswick, Canada, and served as an important coastal defense for the easternmost United States of America during the 19th century.

In 1808, the United States Army decided to build a fort in Eastport, Massachusetts (now Maine), to protect against possible threats from Britain and other European powers then engaged in warfare.

The British demanded that the inhabitants of Eastport take oaths of allegiance to their crown; some complied, others evaded, and many removed to undisputed American territory.

Through negotiations with the British in 1817, Americans renounced their claims to larger islands farther east and regained control over Eastport on 30 June 1818.

Artillery at Fort Sullivan on 15 April 1822, when and where his wife bore his son, future major general Napoleon Jackson Tecumseh Dana.

First Lieutenant George Sears Greene, who would serve as a major general in the Union Army during the American Civil War and was noted for his defense of Culp's Hill at the Battle of Gettysburg, commanded Fort Sullivan from 1831 until 1835.