As road transport developed in the 1930s, containers were introduced to the railways in order to compete. Post World War 2, there was a big drive to promote container traffic by the four railway companies. Each had a door-to-door service, for house moving, using their own road vehicles and flat railway wagons to achieve this. Obviously, this required co-operation between the companies as the road delivery at the other end might well involve the use of vehicles of a different company.

The containers were restricted in design as to what would fit the vehicles and the standard loading gauge of the railways. Containers had their own number codes but, under British Railways, large ones became known as 'B' type and variations were acknowledge by a second letter, for example a 'BD' container. BDs were general merchandise containers and had side doors as well as doors at one end. They became the most widely used container design of their day and had a capacity of 720 cubic feet and a loading limit of 4 tons.

The small size container could be fitted two to a ‘Conflat’ and were known as 'A' type. The 'AF' container was for quick-frozen foods, ice cream etc. and had a rubber-sealed floating door. It could maintain a temperature of -15^oF for 24 hours. There were doors at only one end.

The 'Conflat A' was a post-war Swindon design and the first 400 were built at Swindon and Wolverton. Over the next ten years, 200,000 of them were built, most of them during the BR era. There is little difference between the GWR and BR versions. As delivery had to be made as quickly as possible, the BR 'Conflats' were XP rated. The containers were transferred between rail and road by a yard crane and so they had shackles in the roof for lifting chains to be attached.