Ten concrete gun batteries, including one in the middle of the historic fort, were built from the 1890s through the 1940s, each a response to a particular threat. Atomic bombs, guided missiles, and long-range bombers made such forts obsolete by the end of World War II and the Army abandoned the forts. Following extensive repairs by the National Park Service, the fort was reopened in 1976. [Click here for more info](http://www.nps.gov/guis/planyourvisit/fort-pickens.htm)