Commander John Simon Kerans (30 June 1915 – 12 September 1985) was an officer in the Royal Navy and later a Conservative Party politician.
As British Naval Attaché in China in 1949, Lieutenant Commander Kerans took command of HMS Amethyst when the ship came under fire on the Yangtze River during the final stages of the Chinese Civil War. The ship was detained for ten weeks during negotiations for its release, until Kerans led a night-time escape. Kerans was awarded the DSO Distinguished Service Order. The Amethyst incident was later the subject of a 1957 film called The Story of HMS Amethyst, in which Kerans was portrayed by the British actor Richard Todd.