The S1 Class was introduced in 1907 and was designed by Robinson for the Great Central Railway. They were very powerful 0-8-4 tank locomotives for "hump" shunting at the newly opened Wath-on-Dearne marshalling yard in South Yorkshire. Initially, four were built and although they were generally successful, they sometimes struggled with the heaviest trains. Gresley tried to rectify this by fitting a booster to the trailing bogie., and at the same time two new engines were built bringing the total up to six. The boosters were not totally successful, especially when the locos were running in reverse and they were removed in 1943, but the locos kept their distinctive outside framed rear bogies. They remained employed at Wath, and also at Whitemoor Yard in Cambridgeshire, but were displaced by diesel shunters in the 1950s. By the end of 1953, all six S1s had been moved to Doncaster and had little work to do, although they were occasionally used for for shunting lines of dead locomotives . All six engines were eventually scrapped between 1956 and 1957.