Exploring Abandoned Fort Jefferson — A Historic “Floating Fortress” 70 Miles Beyond Key West

Urban explorer Thomas Kenning takes you on a guided tour of the most stunning abandoned fort in the Western Hemisphere. This is an extended excerpt from Sunshine Sentinels — a guided photographic tour of Florida’s abandoned coastal defenses. Available now from all fine booksellers.

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Visitors to the Dry Tortugas arrive by ferry, seaplane, or private vessel. Two of these sightseers stand atop the northwest bastion of Fort Jefferson (1846), fifty feet above the Gulf of Mexico on the fort’s open upper level, known as the barbette tier. (Photo by Thomas Kenning)

Seventy miles beyond Key West lies a sandy chain of islands devoid of any freshwater. These desert islands make an ideal sanctuary for hundreds of nesting sea turtles and ocean birds. Collectively, they are the aptly-named Dry Tortugas. The shallows that dominate the floor of the Gulf between here and Key West are a natural minefield, slashed where small boats have run aground and scarred with the shipwrecks of those possessed of a deeper draft and less luck. In centuries past, most ships in transit between the northern Gulf and the Atlantic would naturally hew to the navigable passage of deep water that brings them within a cannonball’s shot of these lonely keys.

Thus, the quixotic Fort Jefferson, a floating fortress, Florida’s first theme park — a military fantasia in brick and mortar, comprised of sixteen million blocks forming a two-tiered hexagonal structure complete with firing positions for 420 large guns, arranged so that 125 of them could zero on the same target simultaneously. Its eight-acre parade had room for two massive powder magazines, a three-story thousand-man barracks, officer quarters, and a hospital. There’s also a hotshot furnace for heating cannonballs until they glowed red — the better to ignite the last generation of wooden warships, still in use when this fort was conceived.

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The open casemates of the northeastern wall recede into the afternoon sunlight. Each archway delineates a distinct firing position. Had an enemy ship ever approached — and had the fort ever been armed to its full potential — this design would have allowed 125 guns to zero on any given target all at once. (Photo by Thomas Kenning)

When you see it from the air, before the window of your seaplane is misted over with a salty spray, when you can take the whole thing in at once, Fort Jefferson is an unrivaled colossus. Pure military might astride tiny Garden Key, an awesome American island in command of a wide-open sea — a projection of power that you can’t help but believe.

There’s the theme for your park.

There is exactly nothing understated about Fort Jefferson, a structure that seems to have little regard for the laws of nature.

Built over the course of three decades as a part of the Third System of coastal fortifications, which itself was an ambitious but awkward adolescent phase of the United States’ military ascendency, Fort Jefferson is more stagger than swagger. Its intricate cistern system never worked properly and actually managed to turn its collected rainwater salty. As at other forts in Florida, yellow fever was a serious issue from the moment that work crews of enslaved laborers arrived on Garden Key in 1846.

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(Top) The large parade magazine — the most complete of five planned — dominates the north corner of the eight-acre parade ground. Its arched roof was designed to deflect enemy cannonballs, but advances in rifled artillery — capable of penetrating its brick veneer — made it a giant Achilles heel. It never saw service. (Bottom) Each bastion tower contains gunrooms, magazines, and a granite spiral staircase leading from the parade all the way up to the barbette tier. By design, the spiral steps are considerably narrower at the inside than the outside — a last-ditch defensive measure to throttle traffic up the staircase should intruders ever breach the fort.
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(Top) Since few guns were ever deployed to the fort, many second-tier casemates became prison cells. The fort’s most famous inmate was Dr. Samuel Mudd, who aided a wounded John Wilkes Booth in his escape after Lincoln’s assassination. After an attempted escape in the coal bunker of a supply ship, Mudd settled into life at the fort, helping to stem a yellow fever outbreak in 1867. (Bottom) Each of the freestanding officers’ quarters along the northwest end of the parade featured detached kitchens and outhouses. Despite the prevalence of diseases like yellow fever and scurvy, as well as the persistent threat from heat and hurricanes, some officers brought their families to live at remote Fort Jefferson.

Even as you stand in the overgrown grass amidst cracked foundations on the parade, it’s hard to believe the scale of their work — Fort Jefferson’s two shortest curtain walls measure 325 feet in length, while the remaining four stretch to 477 feet. Most guns are long gone, but the 303 open-vaulted casemates remain, facing toward the sea through tattered embrasures.

Fort Jefferson is audacious in scale. It demands to be shot in widescreen. Vertically it can be described in geological terms.

Into those walls, the sediments of history — the coming of the Civil War, the abolition of slavery, the rise of wage labor — are demarcated as the epochal events that they were. Like a layer of ash from the catastrophic eruption of some ancient volcano, you can see where, four-fifths of the way up the wall, the jaundiced brick produced by enslaved hands in Pensacola gives way to a ruddy variety imported from Maine, baked by anonymous European immigrants and laid by Confederate prisoners of war.

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The onset of the Civil War disrupted supply chains for the incomplete and unarmed Fort Jefferson. The yellowish bricks that comprise the majority of the fort were produced near Pensacola — suddenly out-of-bounds in enemy hands. Construction was completed using red bricks sourced all the way from Maine, as seen near the top of the curtain wall. (Photo by Thomas Kenning)

The fort was largely stripped of its heavy guns and abandoned to the elements by the 1870s. A small caretaker force maintained the hospital as a quarantine station. During this period, it also served as a convenient coaling station for the navy’s Caribbean operations. In fact, in 1898, Fort Jefferson supplied the USS Maine with the coal that would blow it sky high over Havana harbor just days later, igniting the Spanish-American War.

In 1908, the Dry Tortugas became a national wildlife refuge, and in 1992, a national park.

Until recently, you could walk around the entire fort on top of the counterscarp, or moat wall. Successive hurricanes have since shattered that wall, making a complete circuit possible only with snorkeling gear. Even as the National Park Service undertakes conservation projects on features of Fort Jefferson like the Garden Key Lighthouse, it’s not hard to imagine a day in the near future when it’s unsafe to climb up to the barbette tier.

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Like all of the gunports at Fort Jefferson, this iron-reinforced embrasure once featured Totten shutters. These iron shutters would be forced open by the rush of gas produced by a firing artillery piece then rebound shut immediately, shielding the gunners from any incoming fire. (Photo by Thomas Kenning)
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(Top) This 10-inch rifled Parrott gun weighs 27,000 pounds and could fire a 300-pound projectile. While it was capable of hitting targets with a high degree of accuracy, it was also known to explode, posing an extreme hazard to those operating it. As a result, only around forty of this type were ever produced. (Middle) The parapet — a low defensive wall along the edge of the roof — would have offered a limited degree of protection to gunners on the barbette tier. (Bottom) The ineffectual Confederate Navy posed little threat to Fort Jefferson. The captain of an armed Confederate schooner issued the single credible demand for its surrender in January 1861. The fort’s Union commander successfully bluffed that he would destroy the ship unless it retreated; in reality, the unfinished fort possessed no artillery.
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The counterscarp doubles as a breakwater, defending the fort not only from attack, but also wave action and storm surge. Recent hurricanes have caused portions of the wall to collapse, making a complete circumnavigation of the fort possible only with the aid of a snorkel. (Photo by Thomas Kenning)

Fort Jefferson is a relic, a brick-and-mortar cul-de-sac of war-making technology from a time before large caliber rifled artillery could penetrate such brittle walls, before a changing climate threatened to swamp the whole unrealistic scene.

Get on a seaplane, take a ferry — get to Fort Jefferson before antebellum becomes antediluvian.

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From the window of a DHC-3 Otter seaplane, the fort seems to inhabit the exact middle of nowhere. In actuality, it commands a 75-mile-wide strait linking the Gulf and the Atlantic Ocean. Scores of shipwrecks dot the reefs and the vast shallows on either side of the strait. (Photo by Thomas Kenning)

Thomas Kenning’s new book Sunshine Sentinels — a guided photographic tour of Florida’s abandoned coastal defenses — is available now from all fine booksellers.

Sunshine Sentinelsis a stunning visual survey of Florida’s historic coastal defenses — those sun-faded outposts of empire, crumbling now on shifting sands near the end of the beach. It is a guided tour in book form, perfect for these stay-close-to-home kind of times! Seven thrilling tales, supplemented by 140 original images reproduced at the highest quality, providing a view of the Sunshine State that rarely makes the postcard.

You can find additional an additional preview of Sunshine Sentinels on his website, thomaskenning.com.

Follow Thomas on Instagram and Facebook.

Abandoned Florida: Sunshine Sentinels Book Trailer

2 Comments Add yours

    1. Thank you, @danielwalldammit! I hope you get a chance to check out the book!

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