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1.British K class submarines

Six improved versions, K22 to K28 were ordered in October 1917 but the end of the First World War meant that only K26 was completed.

The double hull design (two layers of 'skin') had a reserve of buoyancy of 32.5 percent (a modern nuclear submarine has a reserve of around 13 percent). Although powered on the surface by oil-fired steam turbines, they were also equipped with an 800 hp (0.6 MW) diesel generator to charge the batteries and provide limited propulsive power in the event of problems with the boilers.

They were equipped with four 18 inch (460 mm) torpedo tubes at the bow, two on either beam and another pair in a swivel mounting on the superstructure for night use. The swivel pair were later removed because they were prone to damage in rough seas.
                                                        Loading torpedos.

They were fitted with a proper deckhouse built over and around the conning tower which gave the crew much better protection than the canvas screens which had been fitted in all previous Royal Navy submarines.

The great size of the boats compared to their predecessors led to control and depth keeping problems particularly as efficient telemotor controls had not yet been developed. This was made worse by the estimated maximum diving depth of only 200 ft (60 m) being much less than their length, of 339 ft (103 m). This meant that whilst the bow would almost on the surface, the stern would almost be at its maximum safe depth. The problems were made even more dangerous because the eight internal bulkheads were designed and tested during development to stand a pressure equivalent to only 70 ft (20 m)!

K3 was the first of the class to be completed, in May 1916 and trials showed numerous problems. The most serious was the high temperatures in the boiler room which was to some extent alleviated by installing bigger fans.

Steaming at speed tended to push the bow down into the water making the already poor sea-keeping worse. To fix this a bulbous swan bow was added. (See the picture above of the K5 .) Nevertheless there were still problems, the most embarrassing being that in a heavy sea water could enter the boat through the twin funnels (chimneys) and put the boiler fires out!
                          A later Class Sub.

They suffered numerous accidents, largely caused by their poor manouverability coupled with operating with the surface fleet, and which caused the loss of the following:

• K13 sank on 19 January 1917 during sea trials when an air intake lid failed to close whilst diving and her engine room flooded. She was eventually salvaged and recommissioned as K22 in March 1917.
• K1 collided with K4 off the Danish coast on 18 November 1917 and was scuttled (deliberately sunk) to avoid capture by the enemy (Germans).
• Two boats were lost in an incident known as the "Battle" of May Island on 31 January 1918. The cruiser HMS Fearless collided with the head of a line of submarines, K17, which sank in about 8 minutes, whilst other submarines behind her all turned to avoid her. K4 was struck by K6 which almost cut her in half, and was then struck by K7 before she finally sank with all her crew. At the same time K22 (the rebuilt, recommissioned K13) and K14 collided although both survived. In just 75 minutes, two submarines had been sunk, three badly damaged and 105 crew killed.
• K5 was lost due to unknown reasons during a mock (pretend) battle in the Bay of Biscay on 20 January 1921. Nothing further was heard of her following a signal that she was diving, but wreckage was recovered later that day. It was concluded that she exceeded her safe maximum depth.
• K15 sank at her mooring (where she was tied up) in Portsmouth on 25 June 1921. This was caused by hydraulic oil expanding in the hot weather and contracting overnight as the temperature dropped and the consequent loss of pressure causing diving vents to open. The boat flooded through open hatches as it submerged.

Dive time was around 5 minutes, with the record being 3 minutes 25 seconds which was claimed by K8. The leisurely time allowed the captain the luxury of being able to walk around the superstructure to ensure that the funnels (chimneys) were securely folded down.

The last, improved, boat, K26 was completed slowly, finally being commissioned in 1923. She had six 21 inch (530 mm) bow torpedo tubes but retained the 18 inch (460 mm) beam tubes. Her higher casing almost cured the problems of seawater entering the boiler room and improved ballast tank arrangements cut the diving time to 3 minutes 12 seconds to get to 80 ft (24 m). She also had an increased maximum diving depth of 250 ft (75 m).

                         A later Class Sub.

Most were scrapped between 1921 and 1926 but K26 survived until 1931, only being broken up because her displacement exceeded the limits for submarine displacement in the London Naval Treaty of 1930.

Although the concept of a submarine fast enough to operate with a battle fleet eventually fell out of favour, it was still an important consideration in the design of the Thames class in the late 1920s.

 The K  Class was an attempt to build a submarine to operate with surface fleets, but it suffered a large number of accidents and was described as "the result of an unholy union between a destroyer and a submarine".
References

• DK Brown, The Grand Fleet, warship design and development 1906–1922, 
• Preston, Antony, World's Worst Warships, Conway's Maritime Press, 2002, 
• RN Submarine museum
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