of details not used on the GWR. Stanier realised that there was a need for larger locomotives. These were to be the LMS version of the GWR Halls, but they were not direct copies, as the Hall was too wide to run in most places in Britain. They shared a similar cylinder arrangement (two outside), internal boiler design and size and 6 ft diameter driving wheels.

In their early days the locomotives were known as the "Black Staniers" from their black livery, in