HMS B6 was a Royal Navy B class submarine, built at Vickers, Barrow-in-Furness, launched 30 November 1905 and completed 3 March 1906. B6 was deployed to the Mediterranean soon after the outbreak of World War I. Due to the lack of spare parts this group of submarines were not used after September 1915. In 1917 the Italian Navy converted B6 into to surface patrol boat S6 to serve in the Adriatic. B6 was sold in 1921 to Messrs. Francotosti, Malta.