|Builder:||Vickers Shipbuilding and Engineering, Barrow-in-Furness|
|Laid down:||5 September 1928|
|Launched:||22 August 1929|
|Commissioned:||5 May 1930|
|Fate:||Sunk on 9 June 1931|
|Class and type:||Parthian-class submarine|
|Length:||260 ft (79 m)|
|Beam:||28 ft (8.5 m)|
|Draught:||13 ft 8 in (4.17 m)|
|Range:||8,500 nmi (15,700 km) at 10 kn (12 mph; 19 km/h)|
HMS Poseidon (P99) was a Parthian-class submarine designed and built by Vickers Shipbuilding and Engineering in Barrow-in-Furness for the Royal Navy, launched on 22 August 1929. She spent most of her short career assigned to the Yellow Sea region, based at the Royal Navy's base at Weihai, China. In 1931, the submarine sank after a collision with the steamship Yuta north of Weihai. The submarine was later secretly salvaged by the Chinese in 1972.
At about 12:12 on 9 June 1931, while exercising on the surface with the submarine tender Marazion 20 mi (32 km) north of the vessels' base at Weihai, and despite excellent visibility, Poseidon collided with the Chinese merchant vessel SS Yuta.
Thirty-one of the submarine's crew managed to scramble into the water before the submarine sank to the seabed 130 ft (40 m) below within a few minutes. The aircraft carrier HMS Hermes, heavy cruiser HMS Berwick and sister submarine HMS Perseus led the rescue operations. Poseidon was equipped with Davis Submerged Escape Apparatus which had come into service two years earlier. This was a closed circuit underwater breathing system which provided the wearer with a supply of pure oxygen and a canvas drogue to slow the rate of ascent. Despite the submarine not being equipped with specialised escape compartments or flooding valves, eight of the crew managed to leave the forward end of the boat, although two failed to reach the surface and one died later. Twenty-one crew died in total.
A consequence of the successful escape of part of the crew was to change Admiralty policy from advising crews to wait for the arrival of assistance to attempting to escape from the submarine as soon as possible. This policy was announced in the House of Commons in March 1934.
The secret salvaging of the submarine in 1972 by China's then newly formed underwater recovery units was described in 2002 in an article in the popular Chinese magazine Modern Ships (Chinese: 现代舰船; pinyin: Xiàndài jiàn chuán). This was not known about in the West until the researcher and journalist Steven Schwankert discovered that article with a Google web search and later read it in a Hong Kong library.
In the former British naval cemetery on the island of Liugong, gravestones, bearing clearly legible names, dates and epitaphs of the lost sailors were found in haphazard stacks by historians looking into the sinking of HMS Poseidon and its salvage by the Chinese. The British Ministry of Defence has not received an answer to what became of the remains of the crew. Results of this research are told in Schwankert's book Poseidon: China's Secret Salvage of Britain's Lost Submarine and the documentary film The Poseidon Project.
- Project Azorian – US CIA's secret submarine salvage project (1974)
- "Submarine Casualties Booklet". U.S. Naval Submarine School. 1966. Retrieved 8 September 2009. Cite journal requires
- Lloyd's Register of Ships (PDF). Lloyd's Register of Shipping. 1931. Yuta was a 1,753 GRT cargo ship, built at Aberdeen in 1889 as Yuen Sang and owned in 1931 by Pao Yu Tzai of Newchwang, China
- Gray, Edwyn (2003). Disasters of the Deep A Comprehensive Survey of Submarine Accidents & Disasters. Leo Cooper. pp. 130–131. ISBN 0-85052-987-5.
- "HMS Poseidon". Battleships-Cruisers.co.uk. Retrieved 2 December 2006.
- Paul Kemp (1990). The T-Class submarine - The Classic British Design. Arms and Armour. p. 105. ISBN 0-85368-958-X.
- Zhao, Changxin (赵常信); Zhao, Binghua (赵炳华); Yang, Zhenbo (杨振勃) (2002), "追忆打捞英国"海神"号潜艇 (Remembering the salvage of the British submarine Poseidon)", 现代舰船 (Modern ships) (6), ISSN 1003-2339 (Most of the article's text is behind a paywall, or requires a special plugin)
- Schwankert 2013, pp. 139–141,143–144
- Ryall, Julian (12 June 2009). "China accused of secretly salvaging sunken British submarine containing 18 lost sailors". The Telegraph. London. Retrieved 4 May 2010.
- Ryall, Julian (3 June 2013). "Families of HMS Poseidon victims angry at 'desecration' of graves". The Telegraph. Tokyo. Retrieved 11 June 2013.
- Julian Lewis MP (24 June 2009). "HMS Poseidon - Written answers and statements". Hansard.
- Schwankert, Steven R (2013). Poseidon: China's Secret Salvage of Britain's Lost Submarine. Hong Kong: Hong Kong University Press. ISBN 9789888208180. Retrieved 15 October 2013.; Partial view on Google Books
|Wikimedia Commons has media related to HMS Poseidon (P99).|
- "HMS Poseidon". Battleships-Cruisers.co.uk. Retrieved 11 June 2013.
- "HMS Poseidon". Submariner Association - Barrow in Furness Branch. Retrieved 11 June 2013.
- "Parthian Class Early Patrol Submarine". Britsub. Retrieved 11 June 2013.