HMS D6

The D-class submarines were designed as improved and enlarged versions of the preceding C class, with diesel engines replacing the dangerous petrol engines used earlier. D3 and subsequent boats were slightly larger than the earlier boats. They had a length of 164 feet 7 inches (50.2 m) overall, a beam of 20 feet 5 inches (6.2 m) and a mean draught of 11 feet 5 inches (3.5 m). They displaced 495 long tons (503 t) on the surface and 620 long tons (630 t) submerged.[1] The D-class submarines had a crew of 25 officers and other ranks and were the first to adopt saddle tanks.[2]

For surface running, the boats were powered by two 600-brake-horsepower (447 kW) diesels, each driving one propeller shaft. When submerged each propeller was driven by a 275-horsepower (205 kW) electric motor. They could reach 14 knots (26 km/h; 16 mph) on the surface and 9 knots (17 km/h; 10 mph) underwater. On the surface, the D class had a range of 2,500 nautical miles (4,600 km; 2,900 mi) at 10 knots (19 km/h; 12 mph).[2]

The boats were armed with three 18-inch (45 cm) torpedo tubes, two in the bow and one in the stern. They carried one reload for each tube, a total of six torpedoes.[2]

D6 was laid down on 24 February 1910 by Vickers at their Barrow shipyard, launched 23 October 1911 and was commissioned on 19 April 1912. She was the first British submarine to be equipped with a deck gun when built, a 12-pounder (3-inch/76mm) gun. D6 was sunk by UB-73 73 miles north of Inishtrahull Island off the west coast of Ireland on 24 or 28 June 1918. There were two survivors who were taken prisoner.[3] Their post-war report apparently led the British to conclude that the torpedo that sank her had employed a magnetic pistol.[4]

• Akermann, Paul (2002). Encyclopaedia of British Submarines 1901–1955 (reprint of the 1989 ed.). Penzance, Cornwall: Periscope Publishing. ISBN 1-904381-05-7.
• 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.
• Gardiner, Robert & Gray, Randal, eds. (1985). Conway's All the World's Fighting Ships: 1906–1921. Annapolis, Maryland: Naval Institute Press. ISBN 0-85177-245-5.
• Harrison, A. N. (January 1979). "The Development of HM Submarines From Holland No. 1 (1901) to Porpoise (1930) (BR3043)". Submariners Association: Barrow in Furness Branch. Archived from the original on 19 May 2015. Retrieved 19 August 2015.

• HMS D6 Roll of Honour