Back to the drawing board: The K-class submarine


Design studies for what were to become the K-class submarines began in 1913 in response to a requirement for underwater vessels with the speed and endurance to operate with the Royal Navy’s Grand Fleet. There were doubts that contemporary diesel engines could give the necessary surface speed of 24 knots, so oil-fired steam turbines were proposed. Admiral Jacky Fisher all too accurately remarked that: ‘The most fatal error imaginable would be to put steam engines in submarines.’

A K-class submarine, probably K3, pictured during the First World War. For an underwater vessel, the class had ‘too many damned holes’, as one submariner observed. Image: Wikimedia Commons

Despite such misgivings, the failure of the diesel-powered J-class fleet submarines to reach the required surface speed led to the design of the 18-strong steam-powered K-class. The first of these was K3, completed in May 1916. Sea trials showed that she met all the performance requirements, but revealed a series of problems, including unbearable heat in the boiler room. Despite the fitting of larger cooling fans, this problem was never fully fixed.

Seaworthiness on the surface was another issue – the low freeboard and short funnels meant that in rough weather there was a constant risk of seawater pouring down the funnels and extinguishing the boiler fires. This forced several K-class boats to crawl back to port under auxiliary diesel power. (None of the class was sunk by the enemy, but six were lost in accidents.)

The May Island fiasco

Attempts to use the type in its intended role were thwarted by its technical limitations. According to one commentator, it combined the ‘speed of a destroyer, the turning circle of a battlecruiser, and the bridge-control facilities of a picket boat.’ The worst fiasco was an exercise in the Firth of Forth on 31 January 1918, which degenerated into a series of accidents involving 5th Battle Squadron, 2nd Battlecruiser Squadron, two cruisers, and two flotillas of K-class submarines.

Strengths:  High surface speed, heavy armament
Weaknesses:  Dangerous diving characteristics  and underwater handling, extreme boiler-room heat issues

In what became known as the Battle of May Island, the cruiser HMS Fearless rammed and sank K17. While manoeuvring 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 and K14 collided – although both survived. In just 75 minutes, two submarines were sunk, with three more badly damaged, and 105 crew killed.

The most dangerous faults were associated with diving, which took an average of five minutes. As a contemporary submariner put it, the K-class had ‘too many damned holes’, and a minor obstruction was enough to jam one of the many vents open as the submarine dived.

In December 1916, K3’s trials went badly wrong while the future King George VI was on board: control was lost during a test-dive and her bows stuck in the seabed at a depth of 150ft, with her stern above the surface.

In this case, the crew managed to free her and resurface in 20 minutes or so, but some others were not so lucky. The class was as difficult to handle while submerged as it was on the surface – with a length of 339ft and a maximum ‘safe’ diving depth of 200ft, a dive at any angle greater than 30° meant that the bow would exceed its safe depth while the stern was barely submerged.

This may well have been the cause of the loss of K5 during exercises off the Isles of Scilly after the war, in January 1921.