The Amethyst incident, also known as the Yangtze incident, was an historic event that occurred on the Yangtze River for three months in the summer of 1949, during the late phase of the Chinese Civil War. The incident involved the Communist People's Liberation Army (PLA), who were in the middle of a river-crossing offensive to overthrow the Nationalist Government, and four British Royal Navy ships HMS Amethyst, HMS Black Swan, HMS Consort and HMS London. The British warships, whose right of passage along the Yangtze had been unchallenged previously since the late Qing dynasty, came under bombardment by PLA artillery and were forced to withdraw permanently from Chinese territorial waters.

HMS Amethyst was a modified Black Swan-class sloop of the Royal Navy. She was laid down by Alexander Stephen and Sons of Linthouse, Govan, Scotland on 25 March 1942, launched on 7 May 1943 and commissioned on 2 November 1943, with the pennant number U16. After the Second World War she was modified and redesignated as a frigate, and renumbered F116.