[1][2] They were designed by Wilson Worsdell for mineral traffic.

The cylinder bore was increased by half an inch at the same time.

Some locomotives later had their superheaters removed but the piston valves were retained.

Thirty-four locomotives survived into British Railways ownership in 1948 and their BR numbers were 65600-65644 (with gaps).

British Railways quickly withdrew the remaining locomotives and all had gone by the end of 1951.