The class 6B was a 4-4-0 express locomotive designed by Charles Sacré. 27 were built in the Gorton Shops between 1877 and 1880. They had double frames with outside cranks and a boiler that was very large for a British locomotive of this time. The driving wheels had a diameter of six feet and three inches or 1,905 mm. In their first years, they were used for the most important expresses between Grantham, Retford and Manchester.

In 1884, No. 434 was part of a dramatic accident near Penistone when its crank axle broke. The type of vacuum brake that was in use here had the downside that it was not applied when the line was separated, resulting in 24 dead. Three years later, the MS&LR changed the brakes of their locomotive to the automatic one.

In 1897 the railway became the Great Central Railway, and in the same time these locomotive had been transferred to Cheshire after new locomotives had taken over their original tasks. By this time the diameter of their cylinders had been increased from 17 to 17.5 inches. Robinson rebuilt all with new boilers with smaller tubes and a longer smokebox. The last one was withdrawn in 1930, after they had become LNER class D12.