|Builder:||Armstrong Whitworth, Newcastle upon Tyne|
|Laid down:||October 1915|
|Fate:||Sold, 4 November 1921|
|Class and type:||K-class submarine|
|Length:||339 ft (103 m)|
|Beam:||26 ft 6 in (8.08 m)|
|Draught:||20 ft 11 in (6.38 m)|
|Complement:||59 (6 officers and 53 ratings)|
In 1917, K11 was damaged by fire during a North Sea patrol. She was forced to surface and was towed by a destroyer. K11 was part of the disastrous Battle of May Island exercise. She was forced to take avoiding action to avoid K14, but survived the exercise. K11 was sold on the 4 November 1921.
Like all British K-class submarines, K9 had a displacement of 1,800 long tons (1,800 t) when at the surface and 2,600 long tons (2,600 t) while submerged. It had a total length of 338 feet (103 m), a beam of 26 feet 6 inches (8.08 m), and a draught of 20 ft 11 in (6.38 m). The submarine was powered by two oil-fired Yarrow Shipbuilders boilers and one geared Brown-Curtis or Parsons steam turbine; this developed 10,500 ship horsepower (7,800 kW) to drive two 7 ft 6 in (2.29 m) screws. It also contained four electric motors each producing 350 to 360 horsepower (260 to 270 kW). It was also fitted with a diesel engine providing 800 hp (600 kW) to be used when steam was being raised, or instead of raising steam.
The submarine had a maximum surface speed of 24 kn (44 km/h; 28 mph) and a submerged speed of 9 to 9.5 kn (16.7 to 17.6 km/h). It could operate at depths of 150 ft (46 m) at 2 kn (3.7 km/h) for 80 nmi (150 km). K9 was fitted with a 3 inches (76 mm) anti-aircraft gun, ten 18-inch (460 mm) torpedo tubes, and two 4-inch (100 mm) deck guns. Its torpedo tubes were fitted to the bows, the midship section, and two were mounted on the deck. Its complement was fifty-nine crew members.
- "K for Katastophe". Undersea Warfare Magazine. Archived from the original on 24 September 2015. Retrieved 20 August 2015.
- Colledge, J. J.; Warlow, Ben (2006) . 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. OCLC 67375475.
- Anthony Bruce; William Cogar (27 January 2014). Encyclopedia of Naval History. Routledge. p. 356. ISBN 978-1-135-93534-4.
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- Hutchinson, Robert. Submarines, War Beneath The Waves, from 1776 to the Present Day.