Following on from the Churchward design 1361 class saddle tank engines the design was adapted to the familiar GWR pannier tank layout for a further batch of similar light dockside shunting engines, forming the 1366 class.
These engines were used on similar duties to the earlier 1361s where light tracks, bridges or docksides precluded the use of heavier locomotives. The 1366 class was closely associated with the Weymouth Quay Tramway for many years, hauling passenger and goods trains through the streets and along the quays of Weymouth to the GWR marine divisions' Channel Islands terminal. The class were also used on other lines where light locomotives were needed, including several branches serving china clay dries in Cornwall. Several of the GWRs roundhouse sheds tried to keep a one of these small engines on hand as they would fit into a track with another engine, so could be used to haul 'dead' engines onto the turntable.