This latest title explores the history of the standard classes that emerged after the victory of the diesel-electric school. The follow up to the author s Diesel Pioneers, Hydraulic vs. Electric provides significant primary research into official records accompanied by 175 mono illustrations. As British Rail approached modernisation of its locomotive fleet in the mid-1950s, there were two competing means of using diesel engines in main-line locomotives hydraulic and electric. The former was preferred by a number of railway operators, most notably DB in Germany as the technology was considerably lighter than that required for diesel-electric locomotives of a comparable power. This is perhaps best exemplified by the weight of the 78 ton hydraulic Warship class compared to the electric Class 40, which weighed in at an impressive 133 tons for a virtually identical effort. Following the Modernisation Plan, British Rail acquired both diesel-hydraulic and diesel-electric locomotives. Within the railway industry there were proponents of both forms of traction, with controversy raging amongst the CME s department over the merits or weaknesses of either type. Gradually the proponents of electric transmission, aided by the improvements in design which ultimately led to a considerable reduction in the weight of diesel-electric locomotives, won the day and the hydraulic classes were ultimately to be withdrawn, in many cases well before the types were retired from service.