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Fort Jefferson Military History

When you visit The Dry Tortugas and Fort Jefferson, you are treated to one of the most unique National Parks in the world. These seven islands are a rare combination of natural and historic resources. Not only are you surrounded by a vast expanse of sea, sky, sandy beaches, and coral reef, but you step into a park rich in history including a 19th century fort, The Civil War, and its most famous prisoner, Dr. Samuel Mudd, who was imprisoned for his involvement in the assassination of President Abraham Lincoln.

Ponce de Leon discovered the Dry Tortugas in 1513 when he caught over 100 sea turtles there. Subsequently the islands were referred to as the “Tortugas” (turtles). During the 1600s and 1700s the area around these islands was used by pirates as a base for attacking merchant shipping in the Gulf.


Aerial view of the large wide open space filled in with grass in the middle of Ft. Jefferson in the Dry Tortugas the building of the fort Tablet the building of the fort Mobile
the building of the fort

After the War of 1812 a group of forts from Maine to Texas was envisioned to provide defense for the United States of America. Fort Jefferson was built to protect the southern coastline of the United States and the lifeline of commerce to and from the Mississippi River. The fort was planned to be the greatest of these.

Fort Jefferson itself is a six-sided building constructed of 16 million handmade red bricks. In 1825 a lighthouse was built on Garden Key to provide warning to sailors about the dangers of reefs and shoals surrounding the Dry Tortugas.

In 1908 the area was designated as a bird reserve and transferred to the Department of Agriculture. On January 4, 1935, it was designated by President Franklin Roosevelt as Fort Jefferson National Monument, the first marine area to be so promoted. On October 26, 1992, the monument was upgraded to national park status in a bill signed by President George Bush.


photo of the building of fort jefferson national park the fort Tablet
the fort

Fort Jefferson was built to protect one of the most strategic deepwater anchorages in North America. By fortifying this spacious harbor, the United States maintained an important “advance post” for ships patrolling the Gulf of Mexico and the Straits of Florida. Nestled within the islands and shoals that make up the Dry Tortugas, the harbor offered ships the chance to re– supply, refit, or seek refuge from storms. The location of the Tortugas along one the world’s busiest shipping lanes was its greatest military asset. Though passing ships could easily avoid the largest of Fort Jefferson’s guns, they could not avoid the warships that used its harbor.

The design of the fort called for a three-tiered six-sided 420 heavy-gun fort, with two sides measuring 325 feet, and four sides measuring 477 feet. The walls met at corner bastions, which are large projections designed to allow defensive fire along the faces of the walls they joined. The heavy guns were mounted inside the walls in a string of open casemates, or gunrooms, facing outward toward the sea through large openings called embrasures. Fort Jefferson was designed to be a massive gun platform, impervious to assault, and able to destroy any enemy ships foolhardy enough to come within range of its powerful guns.


Group getting tour of living quarters in Ft. Jefferson living quarters Tablet
living quarters

Living quarters for soldiers and officers, gunpowder magazines, storehouses, and other buildings required to maintain the fort were located on the parade ground inside the fort’s massive brick walls. The Army employed civilian machinists, carpenters, blacksmiths, masons, general laborers, the resident prisoner population, and slaves to help construct the fort. By 1863, during the Civil War, the number of military convicts at Fort Jefferson had increased so significantly that slaves were no longer needed. At the time, there were 22 black slaves employed on the project.


photo of soldiers at fort jefferson the soldiers & their families Tablet
the soldiers & their families

Fort Jefferson’s peak military population was 1,729. In addition, a number of officers brought their families, and a limited number of enlisted personnel brought wives who served as laundresses (typically four per company). There were also lighthouse keepers and their families, cooks, a civilian doctor and his family, and others. In all, there were close to 2,000 people at Fort Jefferson during its peak years.


A view over a canon situated on one of the walss of Ft. Jefferson in the Dry Tortugas the end of military use Tablet
the end of military use

The fort remained in Federal hands throughout the Civil War. With the end of hostilities in 1865, the fort’s population had 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 was desertion. The most common transgression of civilian prisoners was robbery.

By 1888, the military usefulness of Fort Jefferson had waned, and the cost of maintaining the fort due to the effects of frequent hurricanes and the corrosive and debilitating tropical climate could no longer be justified.

In 1888, the Army turned the fort over to the Marine-Hospital Service to be operated as a quarantine station. On January 4, 1935, President Franklin D. Roosevelt, who visited the area by ship, designated the area as Fort Jefferson National Monument.


photo of prison at fort jefferson the fort prison Tablet
the fort prison

Fort Jefferson was also used as a prison for criminals and deserters during and after the Civil War. The most famous of these prisoners was Dr. Samuel Mudd, who was imprisoned for his involvement in the assassination of President Abraham Lincoln.

During its time, Fort Jefferson held over 2,500 prisoners. After its use as a prison, Fort Jefferson became a quarantine station for the Marine-Hospital Service from 1888-1900, during which the location was also used in the Spanish-American War*.

With its rich historical background, Fort Jefferson finally received its designation as a National Monument in 1935, and then upgraded to National Park status by President George Bush in 1992.