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K-class (UK)

Steam-Powered Attack Submarine

United Kingdom | 1917

"Perhaps one of the worst classes of military submarines was the British K-class debuting in World War 1 - six sank in non-combat incidents."

Authored By: Staff Writer | Last Edited: 12/12/2017 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site; No A.I. was used in the generation of this content.
The K-class group of British submarines is regarded as one of the worst (if not the worst) military submersibles in the storied history of the Royal Navy. Twenty-one were planned from the outset though only seventeen were completed during the time of World War 1 (1914-1918) and, of these, six were lost and none to enemy action. The series was in commission from 1917 until 1931 and various builders were involved in their construction: HM Dockyard Portsmouth / Devonport, Armstrong Whitworth, Beardmore and Vickers being just some of the notable names.

Design work on the new "K-class" boats for the Royal Navy began in 1915 as the British commitment to World War 1 continued to grow. The service sought a fast, ocean-going attack platform that would be able to keep pace with the main battlefleet and the "J-class" was built in response but were found to lack the speed needed through their diesel arrangements (24 knots was the required speed). This led to the decision to power a new class of attack submarine through steam.

The arrangement for the K-class therefore involved two oil-fired Yarrow boiler units feeding a pair of Brown-Curtis (or Parsons) geared steam turbines which, in turn, drove a pair of screws. Four electric motors were installed for undersea running and a Vickers diesel generator was to be used for charging the onboard battery pack with the boat surfaced. All told, nearly half of the internal space of K-class was reserved for the powerplant along. The new boats could hope to make speeds reaching 24 knots when surfaced and 8 knots when submerged and range was out to 800 nautical miles. However, the turbines were required to be completed shut off when the boat ran under.

Displacement reached 2,000 tons when surfaced and 2,600 tons when dived. Overall length became 340 feet with a beam measuring 26.5 feet and a draught down to 20.10 feet.

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As an attack platform, the K-class carried 4 x 460mm and 4 x 450mm torpedo tubes (all bow-facing). An additional pair of 18" tubes were fitted on swiveling mounts in early boats but later removed when they were found to affect seaworthiness. For surface work, the boats were equipped with 2 x 4" BL Mk XI deck guns and a single 76mm fitting.

In service, the K-class became one of the poorer submarine offerings in naval history. They were heavy submarine designs that exhibited poor control and equally-poor seakeeping in rough waters and yielded limited diving capabilities. The hulls were tested to rather shallow depths which added a layer of concern and instability. The boiler arrangement was also found to generate a great deal of heat when ran - which proved problematic in the confined spaces of a submarine.

The boats of the K-class were K-1 through K17 and the post-war K26. Many of the group managed to see stained service records with a high loss of life in some cases. K1 accidentally rammed K4 in November of 1917 and was scuttled. K4 herself was nearly sliced in two by K6 and sank (with all souls aboard) after receiving a collision from K7 in the same event of January of 1918 (this after she was run aground at Walney Island back in January of the previous year). K5 was mysteriously lost in the Bay of Biscay during exercises in January of 1921 and K13 sunk during sea trials back in January of 1917. Both K12 and K16 were submerged for a time before the crews were rescued and K15 sank where she berthed for non-combat reasons on June 1921 in Portsmouth.

It was these sorts of incidents are what garnered the group the ominous name of "Kalamity-class".

One of the more notorious instances of bad "K-luck" occurred in December of 1916 when K3 was being tested with the future King George VI on board. Instead of a planned gentle dive the boat inexplicably went nose-down quickly and buried its bow into the seabed, leaving the remainder of the submarine exposed at the water's surface (to further as to the boat's embarrassment, her propellers were still running). After twenty minutes in this position the boat was freed and was able to safely surface. In January of 1917, its boiler room took on water and, in May of 1918, the boat took another nasty unexpected dive which damaged her hull.

K26 was the only boat of the class to be completed after the fighting of World War 1 had ended in November of 1918 and she represented an improved form of the series. Changes included the addition of 6 x 21" torpedo tubes, improved ballast tanks, a higher casing and better (safer) diving capabilities. She was not commissioned until 1923 and managed an existence into 1931 until given up due to the restrictions of the London Naval Treaty regarding submarine displacements. Most of the rest of the class was stripped of their military value early on and unceremoniously scrapped from the period spanning 1921 into 1926.

Of the whole class K7 was the only one to engage an enemy vessel in wartime, this a German U-boat during World War 1. Of course the K7's torpedo hit its target but failed to explode resulting in K7 running away from the engagement - such was the legacy of the forgettable K-class.

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Power & Performance
Those special qualities that separate one sea-going vessel design from another. Performance specifications presented assume optimal operating conditions for K-class (UK).
2 x Yarrow oil-fired boilers with 1 x Parsons or Brown-Curtis geared steam turbines developing 10,500 shaft horsepower to 2 x screws; 4 x Electric motors developing 1,440 horsepower.
24.0 kts
27.6 mph
Surface Speed
15.0 kts
17.3 mph
Submerged Speed
799 nm
920 miles | 1,481 km
The bow-to-stern, port-to-starboard physical qualities of K-class (UK).
339.0 ft
103.33 meters
O/A Length
26.7 ft
8.14 meters
20.1 ft
6.13 meters
Displacement (Submerged)
Available supported armament and special-mission equipment featured in the design of K-class (UK).
4 x 18" (460mm) torpedo tubes
4 x 18" (450mm) torpedo tubes
2 x 18" torpedo tubes on swiveling mounts (later removed).
2 x 4" (102mm) deck guns
1 x 3" (76mm) deck gun
Ships-in-Class (18)
Notable series variants as part of the K-class (UK) family line as relating to the K-class group.
K1; K2; K3; K4; K5; K6; K7; K8; K9; K10; K11; K12; K13; K14; K15; K16; K17; K26
Global operator(s) of the K-class (UK). Nations are displayed by flag, each linked to their respective national naval warfare listing.
National flag of the United Kingdom

[ United Kingdom (retired) ]
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Image of the K-class (UK)
Image from the Public Domain.

Mission Roles
Some designs are single-minded in their approach while others offer a more versatile solution to seaborne requirements.
Some designs stand the test of time while others are doomed to never advance beyond the drawing board; let history be their judge.
Going Further...
K-class (UK) Steam-Powered Attack Submarine appears in the following collections:
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