His second number has the WR prefix and the IWT and IWTD (the "D" stands for Docks) on his records both indicate, as Ady rightly points you to, the Inland Waterways and Transport element of the RE.
The frustration with them (and with his record) is that once posted to France in March 1918, there is no indication of whereabouts he was operating. War diaries for individual sections do not seem to exist although a major effort was in the canals leading from the port at Ouistreham/Caen. Ady's suggestion will bring up a number of things worth reading.
MaxD
