HMS Poseidon (P99) was a Parthian-class submarine constructed by Vickers Shipbuilding and Engineering in Barrow-in-Furness, England, and launched on 22 August 1929. Designed for the Royal Navy, she featured typical specifications of her class, though specific dimensions and armament details are not provided in the source. Her primary operational area was the Yellow Sea, where she was based at the Royal Navy's Weihai naval base in China. During her service, Poseidon was involved in exercises and patrols in East Asian waters. On 9 June 1931, while on the surface exercising with the submarine tender Marazion, she was involved in a tragic collision with the Chinese merchant vessel SS Yuta, approximately 20 miles north of Weihai. Despite clear visibility, the collision occurred at about 12:12, resulting in Poseidon sinking to a depth of 130 feet (40 meters) within minutes. The sinking was catastrophic, but 31 of her crew managed to escape into the water before the submarine became fully submerged. Rescue operations were led by the aircraft carrier HMS Hermes, the heavy cruiser HMS Berwick, and her sister submarine HMS Perseus. Poseidon was equipped with the Davis Submerged Escape Apparatus, a closed-circuit breathing system introduced two years earlier, which enabled some crew members to attempt escape from the sunken vessel. Eight crew members successfully evacuated through the forward end of the submarine, though two of these did not reach the surface and one died later, resulting in a total loss of 21 sailors. The incident prompted significant changes in Royal Navy escape procedures, shifting policy towards encouraging immediate escape attempts rather than waiting for rescue. In a secret operation in 1972, Chinese underwater recovery units salvaged HMS Poseidon, a fact that remained undisclosed for decades. This clandestine salvage was later revealed in Chinese publications and by researchers, leading to diplomatic inquiries. The wreck and the fate of the crew remain a notable chapter in maritime history, highlighting the dangers of early 20th-century submarine service and the enduring mysteries surrounding the vessel's sinking and recovery.

This description has been generated using GPT-4.1-NANO based on the Vessel's wikidata information and then modified by ShipIndex.org staff.