By 1967, the British Railways wagon fleet had fallen to about a third the size of that it had inherited in 1948. This was partly an indication of the fall-off of business for the railways, as an improved road system made road transportation a preferred option for many. Another major contributing factor was the move from coal to oil as a prime source of energy used by industry and the handling of far less coal by the railways. In an attempt at modernising itself, British Rail launched a programme of vigorous marketing in the 1970s and backed this up with a fleet of new wagons for better bulk handling.

The new air-braked vehicles were larger and could travel faster than before and spelt the virtual end of the 10' underframe that had served Britain's railways for so many decades. For the handling of merchandise we saw the introduction of long wheelbase open wagons and vans with 45 tonnes loading capacity. Born into the TOPS era, these quickly received their TOPS codes. The open merchandise wagons had an 'O' prefix and 'A' (for air-brakes) suffix and the middle letter denoted the type. The first OBA was built in 1974 and had a four-part 5-plank drop-side, on each side, as well as higher ends. They were built at Shildon and Ashford and started life in Railfreight maroon livery, later being repainted in grey and red.

Plasmore Ltd makes building blocks from pulverised fuel ash at its plant at Heck, near Doncaster. They hired, and later bought, a fleet of OBA wagons which were repainted in their livery.