Tank wagons formed the largest sector of wagon provision that British Railways left to the private sector to provide. Their purpose is to carry liquids and many kinds travel this way, including petrol, oil, tar, milk, bitumen, industrial chemicals etc..

The RCH wagon design on 10ft wheelbase chassis was confirmed in 1917 and remained unchanged until after the Second World War. Just before the war, wooden frames were dropped and inspection gantries around the tank top manhole began to appear. Many 10ft 14T tank wagons were built during the war for the Petroleum Board and these passed to the private sector after the war.

'B' class tank wagons were painted black. Initially, 'A' class tanks were painted a buff colour with two red rings round the centre of the tank. Just before the outbreak of the Second World War, a silver livery was adopted for 'A' tanks, along with red solebars. As the tank hire business began to get underway, the hire company's logo started to appear on tanks and then, in the mid 1970s, petroleum companies began to remove their own identification. Tank wagons used in other industries were painted according to the taste of the user. Sometimes these were quite colourful and this has helped to make tank wagon models a popular subject with collectors.