HMS K6 was a British K class submarine built by HM Dockyard, Devonport. She was laid down on 8 November 1915 and commissioned in May 1917. K6 was the first of the K class to have its bows raised by converting it into a bulbous swan shape. In 1917, K6 did not surface during a trial in North Dockyard, Devonport. K6 was involved in a serious exercise accident nicknamed the "Battle of May Island". She was responsible for ramming K4 and slicing her in half. She was sold on 13 July 1926 to John Cashmore Ltd for scrapping at Newport.