The British Railways Standard Class 5MT 4-6-0 was one of the 12 standard classes of steam locomotive built by British Railways in the 1950s.It was essentially a development of the LMS Stanier Class 5 4-6-0 ('Black Five'). A total of 172 were built between 1951 and 1957.
William Stanier's Black Five had been the most successful mixed-traffic type in Great Britain.Construction of the Black Fives had started in 1934 and continued past nationalisation to 1951. A new set of 'standard' locomotives was to be built by British Railways, based on LMS designs and incorporating modern ideas.