 It was an enlargement of the T1 with a sloping grate of increased area giving greater power.Drummond drew upon his previous experience with the successful London Brighton and South Coast Railway D1 class, whilst he was works manager at Brighton in the early 1870s, and his own 157 class of 1877, on the North British Railway in Scotland.It was the heaviest 0-4-4 type ever to run in Britain.