They passed to the London and North Eastern Railway at the 1923 grouping, and received the LNER classification Z5.
On delivery these were found to be 2 tons over the maximum weight for operating on the docks,[1] and a further two locomotives of similar design were acquired.
These Class X locomotives, numbered 116 and 117, had smaller driving wheels and a shorter wheelbase.
In order to reduce the weight of the Class Y locos, they initially operated with their tanks only partially filled.
They remained in the GNSR livery of black with red and yellow lining until painted unlined black during World War II, although they gained the letters LNER and subsequently acquired BR emblems.