Merry-go-round train  A merry-go-round train, often abbreviated to MGR, is a block train of hopper wagons which both loads and unloads its cargo while moving. In the United Kingdom, they are most commonly coal trains delivering to power stations. These trains were introduced in the 1960s, and were one of the few innovations of the Beeching axe, along with investment from the CEGB (Central Electricity Generating Board) and the NCB (National Coal Board) into new power stations and loading facilities. West Burton Power Station was used as a testing ground for the MGR system but the first power station to receive its coal by MGR was Cockenzie in Scotland in 1966. It was estimated at the time that the 80 MGR hoppers needed to feed Cockenzie would replace up to 1500 conventional wagons. A 1.2 GW power station, such as Cockenzie, receives up to 3 million tons of coal a year, whereas a larger 2 GW plant, like West Burton, up to 5 million tons per year. By the end of 1966 there were about 900 wagons carrying 53,000 tons a week to four power stations. Power stations that were built to handle the new MGR traffic were Aberthaw, Drax, Didcot, Eggborough, Ferrybridge C, Fiddlers Ferry and Ratcliffe, of which the former and latter pairs are still open for traffic. Many of the older power stations were gradually converted to MGR operation. Merry-go-round operation was also adopted for the Immingham Bulk Terminal built in the early 1970s to supply iron ore to the Scunthorpe Steelworks from the Port of Immingham. There were 11,162 MGR hoppers built. The numbering ranges were 350000-359571, 365000-366129 and 368000-368459  The two prototype wagons, 350000 and 350001, were built at Darlington works in 1964 and 1965 respectively, following which several large batches were constructed at the nearby Shildon works. With the exceptions of the two prototypes built at Darlington and the 160 wagons built at Ashford, all 10,702 HAA wagons and 460 HDA wagons were built there. Most of the early wagons (up to 355396) were originally lettered with B prefix numbers but these were later removed. While the majority of the wagons were built as HAAs, the final batch (built in 1982 as 368000-368459) were coded as HDA to indicate their ability to operate at up to 60 mph when empty instead of the standard 45 mph.