John Speller's Web Pages Derby Lightweight Diesel Multiple Units

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Derby Lightweight Diesel Multiple Units Untitled Untitled
In 1938 Sir William Stanier introduced a stylish silver and red streamlined articulated three-car diesel multiple unit. The prototype unit was built at Derby Works in 1937-38 and equipped with two 125 hp Leyland engines and Lysholm Smith torque converters. The unit was tested on the Oxford to Cambridge line, but was mothballed on the outbreak of World War II and the experiment was not proceeded with.

Instead, after Nationalization, Derby produced what was at the time a revolutionary design in the form of the Derby Lightweight Diesel Multiple Unit. The body and frame of these units were made of a heat-treated high strnegth alloy of aluminium produced by ICI under the brand name of Kynal. Intended primarily for aeroplane fusilages, the alloy consisted of 94.15% aluminium, 4% copper, 0.85% magnesium, 0.6% manganese and 0.5% silicon.

Like the 1938 unit, the first batch of Derby Lightweights were equipped with two 125 hp Leyland engines and Lysholm Smith torque converters, although as a transmission the latter was by then obsolescent. 219 vehicles were built, including the two bodies that became a battery electric unit, and these were arranged in 1,2 and 4-car formations. The first cars entered service in June 1954 in West Yorkshire. Although they did excellent work, the Derby Lightweight units were considered non-standard by British Railways and withdrawn after a comparatively short lifespan. The last of them was withdrawn from passenger service in 1969, though certain units have been preserved. A journey on one of these may be experienced here.

At the time of Nationalization F. W. Hawksworth on the Great Western Railway had been considering lightweight aluminium alloy coaches of a similar design. Metropolitan-Cammell also produced some lightweight diesel multiple units, but it is really only half a century later in the early twenty-first century that lightweight high-strength aluminium alloy has come into its own as a material for making train cars.

LMS streamlined 3-car articulated diesel multiple unit, 1938
Official British Railways photograph of a 2-car Derby Lightweight Diesel Multiple Unit
Official British Railways photograph of the front of a Derby Lightweight Diesel Multiple Unit
Derby Lightweight power car No. 79018, preserved on the the Midland Railway - Butterley, and shown here at Bewdley on the Severn Valley Railway in 2010. Image copyright Our Phellap and licensed for reuse under this GNU Free Documentation License
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