It featured a Belpaire firebox and increased boiler pressure over its predecessor but had the same power rating of 7F.

Among other things this meant that the axle bearings were too small for the loads they had to carry.

Cox, writing in a series of articles in Trains Illustrated c. 1957, suggests that they had a sufficiently modern and effective front end that, for steady slogging, some drivers preferred them to an LMS Stanier Class 8F.

Numbers 9672–74 were fitted with ACFI feedwater heaters when built but these were removed during the Second World War.

All members of the class entered British Railways ownership in 1948, but 122 had been withdrawn by the end of 1951; fifty were withdrawn without receiving their BR number.