Second World War, and experience with the 1935 fleet of battery locomotives showed that these were a better solution. Service DEL120 entered normal service in 1941, but was not a success, as the complicated operating system resulted in frequent breakdowns and repairs. It was used initially around Watford, and was transferred to Hainault to work ballast trains after an overhaul in 1952. It was moved to Golders Green depot temporarily, to operate a works train while an experimental ground wheel lathe was installed. The diesel engine was removed in 1954, after which it was only used for shunting, initially at Hainault and later at Acton. It was not ideal as a shunting engine, as visibility from the cab was poor, and access difficult, and so it was idle from 1956, finally being scrapped in 1958. DL81-DL83 Three Rolls-Royce-engined diesel-hydraulic locomotives were built in 1967–68, and were supplied to an open-cast iron ore mine at Corby. When the iron ore was worked out, the locomotives were surplus to requirements, and were acquired by London Transport in 1971. They were numbered in the range DL81-DL83. All three were standard 0-6-0DH Sentinel diesel shunters obtained from Thomas Hill (Rotherham) Ltd (the Rolls Royce/Sentinel dealer). They were painted dark green and operated at Neasden and Lillie Bridge depots where they replaced the last of the ex-GWR pannier tank steam locomotives. The locomotives had a wheelbase of only , and this was too short to operate the track circuits. Since this made their use impracticable, each was permanently coupled to a tender, which consisted of a bogie removed from a redundant District line Q Stock car. The weight of the bogie was increased to 17 tons, and it was fitted with tripcocks and sleet brushes, so that it could be used for clearing snow and ice from the current rails. Although the tenders were permanently coupled to the locomotives, they carried separate numbers, and were identified as DT81, DT82 and DT83. The tender increased the wheelbase to . One locomotive was normally operational at each of the depots, with the third kept as a spare. Transfers between the works occurred when maintenance or repairs were necessary. Movement outside of the depots was severely restricted when the civil engineering department decided that the short wheelbase and 16-ton axle loading might cause overloading problems on a number of bridges. Both the free end (front) of the locomotive