Of the 17 of the class, six were built at Vickers, each at an estimated cost of £340 000. Originally, 28 K Class submarines were ordered, but of these several were later cancelled. K18 to K21 were redesigned and became the M Class and K26 was an experimental submarine, built in an attempt to overcome the defects of the earlier K boats. At the time, they were not only the largest submarines in the world, but also the fastest - their phenomenal speed being attained from 10 500shp oil-fired steam turbines. In addition to the steam turbines, the class had an auxiliary diesel generator for charging the batteries and powering the electric motors.
The pioneer vessels of the K Class had a flush deck with a slight sheer forward but, because of a tendency to dive into head seas, later boats were redesigned to overcome this alarming habit and were fitted with large clipper bows and buoyancy tanks. In order to allow this change, the armament and torpedo tubes were rearranged - the guns were removed to the superstructure and, where fitted, twin 18-inch deck tubes for use on the surface at night were removed.
The outline of the K boats was broken by two small funnels that were hinged to fold down into a watertight well. The large air-intakes for the two oil-fired boilers also required watertight seals. In the concise words of a contemporary submariner, the K Class had 'too many damned holes', and a minor obstruction or wire rope was sufficient to jam a vent open just as the submarine was ready to dive. An added disadvantage was that the highly ingenious design of the class was so complex that it was vulnerable to minor defects.
K Class submarines could submerge faster than any previous steam submarines, but the delay was still impossibly long. Although the specified time to close down and secure the boiler room, funnel, etc was only 30 seconds, vessels of the K Class till took about five minutes to dive. Once submerged, the class could dive to a depth of 200 feet.
The K boats, being high-speed Fleet submarines, were fitted with a deckhouse built over and around the conning tower, forming, in fact, a fully-enclosed bridge, and giving, for the first time in Royal Navy submarines, protection to bridge personnel other than by canvas screens. K Class submarines began to enter service in 1916, but because of their role with the Fleet they were unduly exposed to the risk of collision, and a chapter of accidents befell the class. The worst accident occurred on the night of 31st January, 1918 when ten K boats were operating with battlecruisers on a night exercise off May Island.
