In 1931, the British submarine HMS Poseidon (P99) sank following a collision with a Chinese merchant vessel near China’s coastline. At the time, the incident captured public attention, but interest quickly waned, and the story faded into relative obscurity.
Many years later, the saga reemerged under startling circumstances. Chinese authorities had secretly raised the submarine from the ocean floor without notifying the British government or any international agencies. The covert operation remained hidden for decades, and its eventual disclosure revived fascination with the long-forgotten loss, sparking renewed discussion over the handling and sovereignty of sunken military vessels.
HMS Poseidon (P99) collides with the SS Yuta
In the early hours of June 9, 1931, HMS Poseidon, a Royal Navy Parthian-class submarine, was performing routine surface exercises off Wēihǎi, China, near a British naval outpost. The morning began with calm seas and clear skies, but catastrophe struck when the submarine collided with the Chinese merchant ship SS Yuta, tearing a large breach along Poseidon’s starboard side.
The damage was devastating. Water rushed in, and the vessel sank rapidly to a depth exceeding 100 feet. Of the 52 sailors aboard, only 31 managed to escape. The Royal Navy quickly mounted a rescue operation, deploying the aircraft carrier HMS Hermes, the heavy cruiser HMS Berwick, and Poseidon’s sister ship, HMS Perseus.
Despite these efforts, the tragedy claimed 21 lives, cementing HMS Poseidon’s sinking as one of the deadliest submarine accidents in Royal Navy history.
Leading to important policy changes
Eight crew members from HMS Poseidon managed to escape using the Davis Submerged Escape Apparatus, an early form of scuba gear. Unfortunately, not all of them survived—two never reached the surface, and another passed away later.
This incident prompted the Royal Navy to rethink its submarine escape procedures. Since some of Poseidon’s crew successfully escaped, the Admiralty decided to change its approach. Instead of instructing crews to remain inside and wait for rescue, they now encouraged immediate escape attempts after a collision. This change was announced in the House of Commons in March 1934.
Additionally, the military began equipping submarines with escape chambers and increased its research into decompression sickness treatment.
China launches a secret salvage mission
For decades after the collision, HMS Poseidon lay untouched on the ocean floor, largely forgotten and seldom mentioned. That changed in 1972, when, amid the upheaval of China’s Cultural Revolution, the nation quietly undertook a secret mission to raise the wreck. Newly established underwater recovery teams carried out the effort in complete secrecy, with the full story only surfacing many years later.
The operation was a formidable challenge, demanding precise coordination to navigate significant technical and logistical obstacles. While China’s true motives remain unclear, some theories suggest the salvage served as a training ground to strengthen recovery capabilities, while others argue it may have been intended to eliminate a possible hazard to navigation.
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.