Fort Andrews was created in 1897 as part of the Coast Defenses of Boston, Massachusetts. Construction began in 1898 and the fort was substantially complete by 1904. The fort was named after Major General George Leonard Andrews, an engineer and Civil War commander, who assisted in the construction of nearby Fort Warren in Boston Harbor. It occupies the entire northeast end of Peddocks Island in Boston Harbor, and was originally called the Peddocks Island Military Reservation. Once an active Coast Artillery post, it was manned by hundreds of soldiers and bristled with mortars and guns that controlled the southern approaches to Boston and Quincy Bay. The fort also served as a prisoner-of-war camp for Italian prisoners during World War II, who were employed as laborers following the Italian surrender to the Allies in 1943. Today, the fort is abandoned, and is managed by the Massachusetts Department of Conservation and Recreation, as part of the Boston Harbor Islands National Recreation Area.

The Harbor Defenses of Boston was a United States Army Coast Artillery Corps harbor defense command. It coordinated the coast defenses of Boston, Massachusetts from 1895 to 1950, beginning with the Endicott program. These included both coast artillery forts and underwater minefields. The command originated circa 1895 as the Boston Artillery District, was renamed Coast Defenses of Boston in 1913, and again renamed Harbor Defenses of Boston in 1925.