K-class steam power bought speed but not endurance

The K class grew substantially larger than the J class and used oil-fired Yarrow boilers with geared steam turbines on the surface, plus electric motors underwater. A single diesel generator had to recharge the batteries, illustrating how tightly machinery competed for internal space. The resulting 24-knot surface speed could match most Royal Navy dreadnought classes and equal the Queen Elizabeth class on paper. The boats also carried a heavy torpedo and gun armament for fleet operations. Yet their range fell to roughly 800 nautical miles at maximum speed, so they acquired the fleet's pace without the legs needed to exploit it consistently.