By adding a trailing axle and reducing the driving wheel diameter by six inches, George Whale developed the Precursor tank class from the Precursor class tender locomotive. It was intended to pull heavy passenger trains on branch lines, but had an axle load that was too high for many branch lines. A total of 50 locomotives were built, the last 20 of which had smaller wheels.
Not only were the cylinders between the frames, but also the leading sandbox. For this reason, the latter was very difficult to refill, which is why a separate filler neck had to be attached to the outside. Since the locomotives could no longer be adapted to growing requirements due to their wheel arrangement, they were all retired between 1927 and 1940.