HMS Subtle (P251)

The last 17 boats of the third batch were significantly modified from the earlier boats. They had a stronger hull, carried more fuel and their armament was revised. The submarines had a length of 217 feet (66.1 m) overall, a beam of 23 feet 9 inches (7.2 m) and a draft of 14 feet 1 inch (4.3 m). They displaced 842 long tons (856 t) on the surface and 990 long tons (1,010 t) submerged.[1] The S-class submarines had a crew of 48 officers and ratings. They had a diving depth of 350 feet (106.7 m).[2]

For surface running, the boats were powered by two 950-brake-horsepower (708 kW) diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 650-horsepower (485 kW) electric motor.[3] They could reach 14.75 knots (27.32 km/h; 16.97 mph) on the surface and 9 knots (17 km/h; 10 mph) underwater.[1] On the surface, the third batch boats had a range of 7,500 nautical miles (13,900 km; 8,600 mi) at 10 knots (19 km/h; 12 mph) and 120 nmi (220 km; 140 mi) at 3 knots (5.6 km/h; 3.5 mph) submerged.[2]

The boats were armed with seven 21-inch (533 mm) torpedo tubes. A half-dozen of these were in the bow and there was one external tube in the stern. They carried six reload torpedoes for the bow tubes for a grand total of thirteen torpedoes. Twelve mines could be carried in lieu of the internally stowed torpedoes. They were also armed with a 3-inch (76 mm) deck gun.[4]

HMS Subtle was constructed by Cammell Laird and launched on 27 January 1944. She survived the Second World War, spending the period between December 1944 and May 1945 with the Eastern Fleet. Here, she sank a Japanese coaster and six sailing vessels. Together with her sister, HMS Statesman, she helped in the tracking and sinking of the Japanese heavy cruiser Haguro.[5] Subtle was finally sold off to be broken up in July 1959 in Charlestown.

• Akermann, Paul (2002). Encyclopaedia of British Submarines 1901–1955 (reprint of the 1989 ed.). Penzance, Cornwall: Periscope Publishing. ISBN 1-904381-05-7.
• Bagnasco, Erminio (1977). Submarines of World War Two. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-962-6.
• Chesneau, Roger, ed. (1980). Conway's All the World's Fighting Ships 1922–1946. Greenwich, UK: Conway Maritime Press. ISBN 0-85177-146-7.
• Colledge, J. J.; Warlow, Ben (2006) [1969]. Ships of the Royal Navy: The Complete Record of all Fighting Ships of the Royal Navy (Rev. ed.). London: Chatham Publishing. ISBN 978-1-86176-281-8.
• McCartney, Innes (2006). British Submarines 1939–1945. New Vanguard. 129. Oxford, UK: Osprey. ISBN 1-84603-007-2.