HDA 368308 at Monk Fryston in May 2001. ©Steve Jones
The fleet of MGR wagons were produced to form block trains of hoppers which both loads and unloads its cargo whilst still moving. They were most commonly used for the delivery of coal to power stations. They were one of the few innovations of the Beeching Axe and were introduced in the 1960s. A vast number of wagons were built and saw use across the UK. Locomotives used with MGR wagons had to be fitted with special electronic speed control equipment that allowed the driver to keep the train steady at a very low speed to aid in the loading and unloading process. The decline of the UK mining industry in the 1980s contributed to making many of these wagons redundant and higher capacity coal hoppers replaced many in the early 2000s. The final MGR working was to Hope Cement Works in August 2010.
(Information provided via Wikipedia)