High Quality Content by WIKIPEDIA articles! 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.