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
