The Bahamas Once Had the World's Only Undersea Post Office

On August 16, 1939, something extraordinary happened off the coast of Nassau in the Bahamas: the world's first—and only—undersea post office opened for business. For three years, divers could descend to the ocean floor, enter a submersible chamber with a thick glass window, and mail letters stamped with the unique postmark "SEA FLOOR".

This wasn't some publicity stunt using a waterproof mailbox. It was an actual functioning post office, authorized by the Bahamas government, where postal workers processed mail at a depth of about 15 feet below the surface.

The Man Behind the Madness

The undersea post office was the brainchild of John Ernest Williamson, an innovative underwater photographer and filmmaker. Williamson's father had invented a flexible observation tube that could pump air to depths exceeding 200 feet. In 1912, Williamson took this concept further by designing the photosphere—a chamber with reinforced glass windows that attached to the tube and could be lowered to the seafloor.

Originally, Williamson used his photosphere to capture groundbreaking underwater footage, including scenes for a 1916 silent film adaptation of Jules Verne's 20,000 Leagues Under the Sea. But in 1939, during the Bahamas-Williamson Undersea Expedition, someone had a brilliant idea: why not turn this underwater observatory into a post office?

Royal Mail from the Deep

The first two letters ever sent from the undersea post office were written by the Governor of the Bahamas himself. He descended through the tube to the photosphere chamber and penned messages to King George VI and President Franklin D. Roosevelt. Imagine being a monarch and receiving mail postmarked from the ocean floor.

For the next three years, until June 25, 1942, the post office operated as both a genuine postal station and a tourist attraction. Divers could purchase special stamps, write postcards, and send genuinely processed mail—all while fish swam past the windows.

Why It Ended

The undersea post office closed in 1942, likely due to World War II disrupting tourism and making such novelty operations impractical. The photosphere was eventually removed, and the seafloor post office became a curious footnote in postal history.

Today, covers (envelope fronts) bearing the "SEA FLOOR" postmark are prized collectibles among stamp enthusiasts. Other countries have since created underwater mailboxes—Japan installed one in 1999, and Vanuatu has an underwater post office at a depth of nearly 10 feet—but none quite capture the audacity of Williamson's original diving-bell post office.

The Bahamas undersea post office remains the only one where postal workers actually worked underwater, processing mail in a pressurized chamber on the ocean floor. It was weird, wonderful, and absolutely real.