|Builder:||HM Dockyard Devonport|
|Laid down:||8 November 1915|
|Launched:||31 May 1916|
|Fate:||Sold, 9 September 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)|
K7 was the only one of the disastrous K class to engage with an enemy; on 16 June 1917 she fired a salvo of torpedoes at the U-boat U-95 and struck a direct hit. However, the torpedo failed to explode with what has been described as typical "K" luck; K-7 escaped retaliation by steaming away at speed.
K7 was involved in an accident with the 4th Light Cruiser Squadron. She was also involved in the catastrophic series of accidents during a night exercise that came to be known sarcastically as the Battle of May Island; K7 was damaged by running over the sinking K4. K7 was sold on 9 September 1921 at Sunderland.
K7 displaced 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 supplying one geared Brown-Curtis or Parsons steam turbine that developed 10,500 ship horsepower (7,800 kW) to drive two 7 ft 6 in (2.29 m) screws. Submerged power came from four electric motors each producing 350 to 360 horsepower (260 to 270 kW). It also had an 800 hp (600 kW) diesel engine 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) 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). K7 was armed with ten 18-inch (460 mm) torpedo tubes, two 4-inch (100 mm) deck guns, and a 3-inch (76 mm) anti-aircraft gun. 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.
- Edwyn Gray (31 January 2016). British Submarines at War: 1914-1918. Pen and Sword. pp. 220–221. ISBN 978-1-4738-5348-5.
- "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.
- Anthony Bruce; William Cogar (27 January 2014). Encyclopedia of Naval History. Routledge. p. 356. ISBN 978-1-135-93534-4.
- Julian Holland (1 May 2012). Amazing & Extraordinary Facts Steam Age. David & Charles. p. 145. ISBN 1-4463-5619-1.
- Hutchinson, Robert. Submarines, War Beneath The Waves, from 1776 to the Present Day.