British Rail Class 52 - Historical Context

Historical Context

When switching to diesel traction as part of the Modernisation Plan of the 1950s, BR designed, and commissioned designs for, a large number of locomotive types. At this time (and arguably right up until Sectorisation in the 1980s), BR's regions had a high degree of autonomy, which extended as far as classes of locomotives ordered and even the design criteria for those locomotives. Whilst almost all other diesel locomotives were diesel-electric, the Western Region employed a policy of using diesel-hydraulic traction, originally commissioning three classes of main line locomotives— a type 2 and two type 4s (later designations class 22, class 41 and class 42). With pressure to increase the speed of the transition from steam to diesel, volume orders for the class 22 and class 42 followed in 1957, a mere two years after the original orders and well before any idea of performance or reliability could be gained. At the same time it was realised that all the existing orders (diesel-electric and diesel-hydraulic) were for types 1, 2 and 4; thus orders were placed for 101 Type 3 diesel-hydraulics (later Class 35). However the increasing demands for more powerful locomotives prompted a further order, in 1961, for 74 diesel-hydraulics of 2,700 hp (2,000 kW); so when the first locomotive was outshopped from Swindon Works in December 1961, less than a year after the order was placed, the Westerns were born.

The theoretical advantage of diesel-hydraulic was simple—it resulted in a lighter locomotive than equivalent diesel-electric transmission. This resulted in better power/weight ratio and decreased track wear. Unfortunately, it had two key disadvantages:

• The technology was proven in continental Europe, particularly Germany but was new to the UK. It was considered politically unacceptable at the time for the UK government to order trains from foreign companies, let alone German companies so soon after the second world war.
• The most robust hydraulic transmissions were only capable of handling engines with power output of around 1500 hp (1120 kW); to build a more powerful locomotive would involve two diesel engines and two transmissions.

Experience showed that the Bristol-Siddeley-Maybach engines were superior to those made by NBL-MAN and although the use of twin engines in the same locomotive was new, the process did not produce any insurmountable problems. In the end the diesel-hydraulic experiment foundered on low fleet numbers, poor maintenance conditions and design issues; not on its German heritage or development of a novel configuration.