 HMS Swordfish was an experimental submarine built for the Royal Navy before the First World War to meet the Navy 's goal of an " overseas " submarine capable of 20 knots ( 37 km / h ; 23 mph ) on the surface . Diesel engines of the period were unreliable and not very powerful so steam turbines were proposed instead to meet the RN 's requirement . Swordfish proved to be slower than designed and unstable while surfacing , and consequently she was modified as an anti @-@ submarine patrol vessel in 1917 . She was paid off before the end of the war and sold for scrapping in 1922 . 
