18 Class WT locomotives were built at Derby Works in England to the design of George Ivatt between 1946 and 1950, numbered 1–10 and 50–57.

This was on spoil trains that transported fill for motorway construction from the Blue Circle cement works at Magheramorne to Greencastle near Belfast.

[1] The RPSI was considering the possibility of building a new member of the class (No.58) to give them a second mainline tank locomotive considering the low availability of turntables on modern day lines.

However, a NCC Class W Mogul is being built instead, due to the longer range between coaling and watering allowed by a tender engine.

[5] The locomotives were built with many LMS standard features such as a self-cleaning smokebox, rocking firegrate, self-emptying ashpan, side window cab and a simplified footplate together with others which followed NCC practice, such as a water top-feed on a parallel boiler (as opposed to the taper boilers being used by the LMS at the time), Dreadnought type vacuum brake gear, Detroit sight feed cylinder lubricator and a cast number plate.