Fort Drum, also known as El Fraile Island (Tagalog: Pulo ng El Fraile), is a heavily fortified island situated at the mouth of Manila Bay in the Philippines, due south of Corregidor Island. Nicknamed a "concrete battleship", the reinforced concrete sea fort, shaped like a battleship, was built by the United States in 1909 as one of the harbor defenses at the wider South Channel entrance to the Bay during the American colonial period.