HMS B8 was a Royal Navy B class submarine, built at Vickers, Barrow-in-Furness, launched 23 January 1906 and completed 10 April 1906. B8 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 B8 into to surface patrol boat S8 to serve in the Adriatic. B8 was sold on 31 October 1919 in Malta.