The 1913 fleet-submarine concept called for boats that could sweep ahead of the Grand Fleet, dive toward an approaching enemy, and attack with torpedoes while the battleships fired from farther away. HMS Nautilus and HMS Swordfish tested possible approaches, followed by the disappointing J class and the steam-powered K class. The K boats reached about 24 knots on the surface, meeting the speed requirement for accompanying the fleet. Their oil-fired boilers needed outside air and an exhaust route, however, creating openings into the submarine that had to be sealed before diving. Later nuclear-powered submarines could use steam turbines without the same need to burn oil. Seventeen of the planned twenty-one K boats were built. Their accident-prone design failed in close operations with the surface fleet, although their size and range made them more useful as independent long-range submarines.
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K-class submarines chased surface-fleet speed
The K class used steam turbines to reach fleet speed, but funnels, boilers, and the transition to diving imposed dangerous complexity on a submarine.