In order to achieve the required surface speed to 24 knots, the K Class submarines needed far more power, so in addition to a diesel generator and batteries they had twin oil-fired boilers that drove a steam turbine. As a result the K Class were were 339 feet long and displaced 1980 tonnes, double the length and three times the weight of the E Class submarine and as big as a destroyer.
Supplying sufficient air to the boilers for combustion meant having five 37 inch diameter air intakes on the stern with a pair of five-foot-tall funnels which allowed the engine fumes to escape. Both funnels and air intakes were closed and sealed by electric motors prior to diving, so average dive time was five minutes. Crash dives were impossible.
Once in service, more serious issues became apparent. HMS K3, the lead ship of the class, was commissioned in summer 1916. Long and heavy, control during diving proved challenging. During one test dive she burrowed into the sea bed while the future King George VI was on board!
She was certainly fast – it was not until the advent of nuclear powered submarines that similar surface speeds were achieved – but when steaming in rough seas, water entered the funnels extinguishing the boiler fires and potentially flooding the boiler room. It was flooding that caused K13 to sink in January 1917, when an inlet failed to close properly.
The biggest problem with the K Class, however, was that they were far less manoeuvrable than the warships they were expected to sail alongside. In November 1917, K4 collided with K1 during an operation off the Danish coast, when she had to turn suddenly to avoid three cruisers in the flotilla.
The following January there was a similar disaster, but with far worse consequences, during an exercise in the Firth of Forth. Sailing in the dark, the flotilla had to alter course sharply to avoid unsuspected vessels in the area, setting off a chain of collisions that resulted in the loss of K4 and K17, along with 104 men. Three other submarines were badly damaged.
By the end of the First World War, four K Class submarines had been lost, none due to enemy action. Things failed to improve in peacetime. K5 disappeared during a mock battle in 1921; an investigation concluded that she had exceeded her safe depth (which was only 200 feet).
Later that year K15 sank while moored in Portsmouth when hydraulic failure allowed vents to open and flood the vessel. Six of the 18 K Class submarines were lost in accidents. Small wonder that sailors nicknamed it the Kalamity class.