What military installation that defended the eastern entrance to Long Island Sound as part of the Harbor Defenses of Long Island Sound is on Fishers Island?
Fort Michie: Fort Michie was a United States Army coastal defense site on Great Gull Island, New York. Fort Michie:  Along with Fort H. G. Wright, Fort Terry, and Camp Hero, it defended the eastern entrance to Long Island Sound as part of the Harbor Defenses of Long Island Sound, thus defending Connecticut's ports and the north shore of Long Island. Fort H. G. Wright: Fort H. G. Wright was a United States military installation on Fishers Island in the town of Southold, New York, just two miles off the coast of southeastern Connecticut, but technically in New York.
Fort H. G. Wright