Nobody knew that China secretly salvaged a British submarine from the ocean floor until thirty years later

In 1931, the British Royal Navy experienced the loss of one of its long-range submarines, less than two years after the vessel was put into service. The incident, involving the collision of HMS Poseidon (P99) with a Chinese cargo ship, served as a tragic and informative lesson. Although this event sparked some controversy, it was not the primary focus of public curiosity. What captures most people's interest is that China secretly salvaged the wreck many years later.

HMS Poseidon (P99) collides with the SS Yuta

On June 9, 1931, HMS Poseidon , a Parthian -class submarine, was engaged in surface exercises off the coast of a leased naval base near Wēihǎi, China. Despite good visibility, the submarine collided with the Chinese merchant vessel SS Yuta , resulting in a large hole in Poseidon 's starboard hull.

Within moments, Poseidon began to sink, causing her crew to scramble for safety; there was little time for evacuation. Of all of the crew members on board, only 31 sailors were able to escape before the submarine plunged to the ocean floor, more than 100 feet below.

The rescue operation included the aircraft carrier HMS Hermes (95), the heavy cruiser HMS Berwick (65), and Poseidon 's sister submarine HMS Perseus (N36). Despite these efforts, the incident led to the loss of 21 crew members.

Leading to important policy changes

Remarkably, eight crew members aboard HMS Poseidon escaped using the Davis Submerged Escape Apparatus , a very early version of scuba gear. However, not all were fortunate; two of the eight didn't reach the surface, and one later died.

The incident led to significant changes in Royal Navy policy regarding submarine escape procedures; the successful escape of some of Poseidon 's crew prompted the Admiralty to revise its policy. Previously, crews were advised to wait to be rescued, but post-collision, emphasis shifted to immediate escape attempts. This was announced in the House of Commons in March 1934.

On top of this, the military began installing escape chambers on submarines and delved deeper into treatment of decompression.

China launches a secret salvage mission

The wreck of HMS Poseidon was left on the ocean floor after the collision and for decades lay undisturbed; there was little discussion or interest in the wreck.

In 1972, during the Cultural Revolution , China conducted a secret mission to salvage the wreck of Poseidon . The operation, conducted by newly-formed underwater recovery units, was shrouded in secrecy, with details only emerging decades later.

The mission was a complex endeavor, involving significant logistical and technical challenges. The reasons behind it are still unknown, with theories ranging from China wanting to test its recovery capabilities to clearing a navigational hazard.

Keeping the salvage of HMS Poseidon (P99) under wraps

The salvage operation was kept under wraps for decades, and it wasn’t until 2002 that the first hints came out, thanks to an article in the Chinese magazine Modern Ships . This piqued the interest of researchers, leading to further investigations.

The West learned of the mission through Steven Schwankert, an American journalist and diving enthusiast. Schwankert stumbled upon the story during his research and was intrigued by the lack of information out there. His work led him to Hong Kong, where he uncovered the details of the 1972 salvage. He also came across testimony from a man who claimed to have witnessed the vessel being pulled from the ocean.

Schwankert published his six years of research in the book, Poseidon: China's Secret Salvage of Britain's Lost Submarine , and the mission was covered in a 2013 documentary, The Poseidon Project.

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These revelations sparked renewed interest in Poseidon and her crew, and the British government sought an explanation from China, leading to several diplomatic discussions.