The distinctive designs by James Pearson, the railway company's engineer, featured single large flangeless driving wheels and two supporting bogies.

The water was carried in both well and back tanks, leaving the boilers exposed in the same way as tender locomotives.

The large wheels gave these locomotives a good turn of speed, 81.8 mph being reported on one train descending Wellington Bank in Somerset.

39, recently renumbered as GWR 2001, derailed at Long Ashton near Bristol on 27 July 1876 and was withdrawn from service.

While the poor condition of the track was a contributing factor, it was decided to rebuild the remaining three express 4-2-4Ts to more conventional 4-2-2 tender locomotives.