Historic Markers Across Florida

Fort Jefferson - Gunrooms

Marker ID:  
Location: On the grounds of Fort Jefferson, Dry Tortugas National Park
County: Monroe
Coordinates: N 24° 37.674    W 082° 52.368
  24.6279    -82.8728
Style: Interpretative Sign **
Waymark: WMPYR0


Fort Jefferson

—Dry Tortugas National Park —

The 8- and 10-inch columbiads were standard U.S. cannon for coast defense. They were cast-iron, muzzle-loading smoothbores. The 8-inch weighed 9,210 pounds and when elevated 4" threw a 65-pound ball about a mile. From the top of the fort, the 10-inchers, 400 pounders could be elevated to 39" and throw a 128-pound shell over three miles.

The fort had no guns when Major L.G. Arnold and his 66 artillerymen arrived from Boston, January 19, 1861 As they worked on the first gun mount, a courier from an armed vessel came ashore and demanded surrender in the State of Florida. When Arnold met the messenger, he rushed to his gunport "Tell your captain," he shouted to the messenger, "I will blow his ship out of the water if he's not gone in ten minutes!"

The bluff worked. By the time war began in April, Arnold had mounted 68 cannon.

Technically, gunrooms are “casemates." This fort has 303 of them. A thick wall in front and strong vaulting above protected guns and men from enemy fire. Open backs and overhead vents carried off heat and smoke.

Though designed to deliver the most concentrated firepower of its time, Fort Jackson never received more than 141 guns—a third of its full armament—because of structural failure.

National Park Service, US Department of Interior.