and the tender were fitted with 'Ward' type couplers as well as normal buffers and couplings to allow them the couple to almost any Departmental rolling stock (at the time). The locomotives had all been withdrawn from service by March 1993, as engineers trains were no longer operated from Neasden Depot. Two locomotives were subsequently preserved; no. DL82 on the Mid-Norfolk Railway and no. DL83 on the Nene Valley Railway. The third locomotive, no. DL81, was sold for further use with an industrial user. Schöma In connection with the construction of the Jubilee Line Extension project, fourteen diesel-hydraulic locomotives were purchased from Schöma of Germany to assist in equipping the tunnels prior to electrification. Weighing 33.88 tonnes each, they are long, and are powered by six-cylinder inline diesel engines, which give them a maximum speed of . They entered service from February 1996, are built to tube tunnel loading gauge, and were fitted with buckeye couplers when built. They are equipped with exhaust scrubbers to prevent soot and other particles from being expelled into the tunnels. The locomotives have since been used on other engineering projects. When not in use they can be found at Lillie Bridge Depot or Ruislip depot. Following the completion of the Jubilee Line extension, ownership of the vehicles was transferred to London Underground Transplant. Numbers 1 and 5 have been modified by fitting Wedgelock couplers so that they can be used to shunt tube stock, whilst numbers 3 and 6 have been fitted with emergency couplers. Leased locomotives Class 66 Metronet contracted five newly built Class 66 locomotives from GB Railfreight in order to speed up track replacement works on the London Underground network. They were first used in August 2006, pulling engineering trains consisting of wagons and high-output track laying equipment nearly long. The locomotives are capable of hauling consists with a maximum length of , thus reducing from 30 to 8 the number of trains needed to supply materials to relay a typical weekend possession of track, and as a consequence increasing the amount of track that can be renewed. One disadvantage of the heavier locomotives is that bridges on the District line needed to be strengthened to carry the extra weight. While working on the network, they are restricted to a maximum speed of , since they are not fitted with tripcocks, and the signalling infrastructure is only designed to cope with