We have visited Fort Jefferson several times and is the crown jewel of Third System forts, of any fort we have been to this is my favorite.
Visiting Fort Jefferson involve a 2 1/2 hour ferry trip from Key West to the Dry Tortugas. The current ferry, the Yankee Freedom III, makes for an easy ride out to the island but when have been on trips where most people have been getting sick because of the rough ocean.
Designed as the largest Third System brick and masonry fort in the U.S. Fort Jefferson was to be a three-tiered six-sided 420 heavy gun fort, with two sides measuring 325 feet, four sides measuring 477 feet and bastions at each corner. Some 16 millon bricks were used in its actual construction. Prior to the U.S. Civil War the bricks came from Pensacola and were yellowish in color, during and after the war the bricks came from Maine and were red in color. The line of construction where the bricks changed can be see at the very top of the fort Walls. The guns were to be mounted inside the walls in a string of 303 open vaulted casemates, facing toward the sea through large Totten embrasures, and along the top barbette tier. The third tier of casemates was never built.
The fort depended upon rain water as the only source of fresh water on the island and an elaborate system of cisterns was built into the foundations of the fort to catch and filter the rainwater. The cistern system failed after cracks developed in the cisterns because the foundations of the fort settled unevenly. The fort suffers from a lack of fresh water to this day.
The fort remained in federal hands throughout the Civil War. With the end of hostilities in 1865, the fort's population declined to 1,013, consisting of 486 soldiers or civilians and 527 prisoners. The great majority of prisoners at Fort Jefferson were Army privates whose most common transgression had been desertion, while the most frequent transgression for the civilian prisoners was robbery. However, in July 1865 four special civilian prisoners arrived. These were Dr. Samuel Mudd, Edmund Spangler, Samuel Arnold, and Michael O'Laughlen, who had been convicted of conspiracy in the assassination of President Abraham Lincoln.
On January 4, 1935, President Franklin D. Roosevelt, who visited the area by ship, designated the area as Fort Jefferson National Monument. It was listed on the National Register of Historic Places on November 10, 1970. On October 26, 1992 the Dry Tortugas, including Fort Jefferson, was established as a National Park.