Fort Duvall was a Coast Artillery fort, part of the Harbor Defenses of Boston, in Massachusetts. What was then called Hog Island in Hull, Massachusetts was acquired by the U.S. government in 1917, and the fort was constructed in the early 1920s. It had only one gun battery, Battery Long, but it mounted the largest caliber weapons in the entire harbor defense system: a pair of 16-inch guns. These were the 16-inch gun M1919, of which only seven were deployed; 16-inch weapons deployed later were supplied by the Navy.