In 1513, Juan Ponce de León discovered the islands located about 70 miles west of Key West. He called them Las Tortugas because of their abundance of large sea turtles. The word "dry" was added later to warn mariners of the lack of fresh water on the island.
Because of Dry Tortugas' strategic location in the Florida Straits, the U.S. military started the construction of Fort Jefferson in 1846. However, the invention of the rifled cannon made the fort obsolete and it was never completed.
During the Civil War, Union warships used the harbor in their campaign to blockade Southern shipping. The fort was also used as a prison, mainly for Union deserters.
In 1992, the islands became Dry Tortugas National Park in an effort to protect their historical and natural features.
Information provided by the National Park Service Web site.