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 28 feet (8.5 m) long, and are powered by 500-horsepower (370 kW) six-cylinder inline diesel engines, which give them a maximum speed of 31 mph (50 km/h). 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.