37412 leads a train of CDA wagons at Parr in May 1992. ©Jon Gavin
British Rail built a fleet of HAA hopper wagons in the 1960s and 1970s which were designed to deliver coal to power stations without having to stop to load or unload. A small fleet of CDA wagons were built to a similar design of the earlier HAA merry-go-round stock for use on china clay traffic in the south-west of England. These new wagons were to displace the aging fleet of wooden 'Clayhood' wagons and featured a rolling roof to protect the material inside. A later batch was produced which were converted from existing redundant HAA wagons. Some of these wagons can still be seen in use today.