At the outbreak of World War II, and with need for a quick expansion in railway carrying capacity, the then Ministry of Transport (MoT) developed a specification for a standard 16-long-ton wagon:
2 axles/4 wheels
9 feet (2.74 m) wheel base
16 feet 6 inches (5.03 m) total length over headstocks
2 side doors and 1 end door
On creation of British Railways (BR) in 1948 – which took control of all railway assets, including all private owner wagons – the new organisation inherited 55,000 original MoT wagons. Officially termed “MCO/MCV 16t Mineral Wagons”, they were all given a “B” prefix in their 5-figure numbering.
BR through various large orders eventually brought the total number of wagons to over 300,000. This included a late-1950s order towards the end of their construction. Mineral wagons were phased out by BR in the 1970s, following reduction in demand for household coal and the development of merry-go-round trains, which used much larger (and braked) hopper wagons.