In 1986, Florida sank this 189-foot ship off the Florida Keys; decades later, its stripped superstructure is covered in sponges, corals and hydroids

What was once a military vessel, a lightning research ship and an industrial piece of equipment now lies beneath the waters of the Florida Keys, covered in sponges, corals and hydroids.

The Thunderbolt, a 189-foot vessel, was deliberately sunk in 1986 to create an artificial reef off Marathon. Nearly four decades later, the wreck has become part of the marine ecosystem, offering shelter and surfaces for a variety of underwater organisms.

Where is the Thunderbolt shipwreck?

The Thunderbolt was intentionally sunk on 6 March 1986 in about 120 feet of water, roughly four miles south of Marathon and Key Colony Beach in the Florida Keys.


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The vessel came to rest upright and intact on the sandy seabed. Its location and structure have made it a popular artificial reef and a notable underwater site in the Florida Keys.

According to NOAA's shipwreck records, parts of the wreck rise considerably closer to the surface. Its cable-handling reel is positioned at around 80 feet, while the observation deck is approximately 75 feet below the surface. The rudder and propellers remain close to the seabed at about 120 feet.

Thunderbolt began life as a World War II vessel

The ship's story began decades before it became an artificial reef.

Originally named Major General Wallace F. Randolph, the vessel was launched on 2 June 1942. It was one of 16 vessels built by the Marietta Manufacturing Company in Point Pleasant, West Virginia.

During World War II, the vessel was designed for the US Army's Coast Artillery Corps to plant and maintain defensive coastal minefields.

After these responsibilities were transferred to the US Navy in 1949, the vessel became surplus military equipment. It was placed in the Naval Reserve Fleet and stored at locations in South Carolina and Florida.

How the ship became a lightning research vessel

The vessel's career took an unusual turn after its military service.

In 1961, Caribbean Enterprises of Miami purchased the ship. It was later acquired by Florida Power and Light, which used it for research into the electrical energy associated with lightning strikes.

During this period, the vessel was renamed Thunderbolt, a name that would remain with it when its working life eventually came to an end.

After the research programme, the ship was donated to the Florida Keys Artificial Reef Association, which prepared it for deliberate placement on the seafloor.

Thunderbolt was stripped before being sunk

The vessel was significantly prepared before its deployment as an artificial reef. Most of its equipment and structures were removed, leaving several major features that could provide a complex underwater habitat.

Among the prominent remaining structures were a large horizontal cable-handling reel on the forecastle deck and the ship's main superstructure, including its observation deck.

Part of the rear section of the superstructure was also cut away, exposing the interior of the hull around the engineering area. The rudder and propellers were retained near the stern.

These remaining structures created multiple levels and surfaces for marine organisms to colonise after the wreck reached the seabed.

What happened to the Thunderbolt after it sank?

The ship did not become a thriving reef overnight. Instead, marine organisms gradually settled on and around the structure after it was placed underwater.

Today, the wreck's superstructure is covered with sponges, corals and hydroids, according to the Florida Keys National Marine Sanctuary.

The growth has transformed the former military and research vessel into a three-dimensional marine habitat. Its surfaces provide places where reef organisms can attach and grow, while the structure itself can offer shelter for marine life.

Why are artificial reefs important?

Artificial reefs are human-made structures placed underwater to replicate some of the characteristics of natural reef habitats.

Ships can be particularly useful because their large, complex structures create numerous surfaces and spaces for marine organisms. Other materials used to create artificial reefs include limestone, steel and concrete.

Once established, these structures can support communities of corals, sponges, fish and other marine invertebrates.

The Thunderbolt illustrates how a deliberately placed wreck can gradually become integrated into its surrounding marine environment.

Sponges and corals now cover the shipwreck

The organisms growing on the Thunderbolt are not simply decorative additions to the wreck.

Sponges, for example, play an important role in reef ecosystems by filtering water and removing bacteria, particles and nutrients. The wider reef environment in the Florida Keys also provides habitat for species such as lobsters, stone crabs and juvenile fish.

However, artificial reefs are not automatically beneficial in every situation. NOAA has noted that properly planned and managed artificial reef projects can provide habitat, while unsuitable materials or illegal dumping can create marine debris and environmental problems.

For the Thunderbolt, however, the decades since its 1986 sinking have brought a remarkable transformation. A vessel that once served wartime and industrial purposes has become a permanent underwater structure supporting a growing marine community off the Florida Keys.