In his short career as Chief Mechanical Engineer at the LMS, Charles Fairburn designed only one steam locomotive. This was a direct development of Stanier's 2-6-4T, having a shorter rigid wheelbase to be able to negotiate tighter curves. This also led to a weight that was 3 tons 8 cwt lighter.
236 were built for the LMS and BR at Derby between 1945 and 1950. In 1950 and 1951, 41 more were built at Brighton for the Southern Region. They also formed the basis for the BR Standard class 4 tank. Withdrawals took place between 1961 and 1967 and two are surviving at the Lakeside and Haverthwaite Railway. As of 2024, 42073 is operational and 42085 is being overhauled. 