<P> Work was half complete in 1860 . Construction continued into the American Civil War, but eventually stopped, and the fort was used as a military prison . It was here that Dr. Samuel Mudd and three others charged with conspiracy in the assassination of President Abraham Lincoln were imprisoned . Mudd was pardoned in 1869 after averting a viral outbreak . This use as a military prison continued until 1874 . With the introduction of coal - fueled ships, the Dry Tortugas became a coaling station for U.S. Navy ships . </P> <P> Fort Jefferson is a massive but unfinished coastal fortress . It is the largest masonry structure in the Western Hemisphere, and is composed of more than 16 million bricks . </P> <P> Comprising 47,125 acres (19,071 ha), Fort Jefferson National Monument was designated by President Franklin D. Roosevelt under the Antiquities Act on January 4, 1935 . The monument was expanded in 1983 and redesignated as Dry Tortugas National Park on October 26, 1992, by an act of Congress . Dry Tortugas is managed by the staff of Everglades National Park . The park was established to protect the island and marine ecosystems of the Dry Tortugas, to preserve Fort Jefferson and submerged cultural resources such as shipwrecks, and to allow for public access in a regulated manner . </P> <P> During the Federal government shutdown of 1995 and 1996, Dry Tortugas was closed along with all other national parks . Seeing this as having a damaging effect on their tourism - dependent economy, the residents of Key West, Florida, raised money to keep Dry Tortugas open . The effort was inspired by the Smithsonian Institution, which raised private donations to keep its museums open during the shutdown . </P>

When did dry tortugas become a national park