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 refused to surface during a submerged 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. K6 was sold on 13 July 1926 at Newport.