Constraints on the locomotive design meant that the coupled wheelbase had to be as short as possible to negotiate the curves in the dock areas but the locomotive had to have sufficient power available for the increasing load of the trains.
Under the system employed by the Great Southern Railways they became Class J11. The class survived until the mid to late 1950s, still working in the Cork area.
References
Clements, Jeremy & McMahon, Michael (2008). Locomotives of the GSR. Newtownards: Colourpoint Books. pp.84–85. ISBN978-1-906578-26-8.