In the late 1950s London Transport sought replacements for the steam locomotives in use on engineering trains, mostly consisting of hauling ballast, sleepers and rail for renewal works and removing spoil, including the old ballast materials to the waste tip. The locomotives then in use had been built for the Metropolitan Railway, before the formation of LT in the 1930s and many were in need of extensive and expensive overhauls.
Several BR locomotives were considered, but the BR shunters were discounted primarily due to their limited maximum speed and larger locomotives would not fit the Metropolitan line tunnels. BR had a number of surplus steam shunting engines available at scrap prices, much lower than the cost of purpose-designed diesel. After trials of a GNR saddle tank, that was found to be in poor condition and the large tank blocked forward vision, a GWR pannier tank was considered superior and accepted!.
The engine had a modern and efficient boiler design, allied to a good chassis, providing a smooth ride at speeds that could be accommodated by the passenger timetable. The pannier tanks allowed a good view ahead for the crew from within the cab, vital in the tunnel sections and only minor alterations to cab handrails and rainstrips were needed to fit the loading gauge. Prices were requested from BR for a number of similar engines, overhauled and altered at Swindon to LT requirements and delivered with a stock of spare parts.
LTs' panniers served until 1971, the last standard gauge steam locomotives operating on the national rail network.