British Rail Class 35 Hymek

The BR Class 35 Hymek was a class of 101 B-B diesel-hydraulic locomotives built by Beyer Peacock of Manchester between 1961 and 1964 for the Western Region, powered by a Bristol Siddeley/Maybach MD870 sixteen-cylinder engine producing 1,700 hp with Mekydro hydraulic transmission. The Hymek — the name derived from the hydraulic Mekydro transmission system — was the most successful of the Western Region's diesel-hydraulic types in terms of reliability and crew appreciation, and for a period in the early 1960s was the WR's standard Type 3 mixed-traffic locomotive on a wide range of secondary express and freight duties.

The Western Region's commitment to diesel-hydraulic transmission — in contrast to the diesel-electric chosen by all other BR regions — was a deliberate policy decision by the WR's management and engineering staff, who believed that the German Voith and Mekydro hydraulic systems offered weight advantages and mechanical simplicity over the electric transmission systems. The Hymek's Mekydro K184U transmission gave smooth power delivery and allowed the locomotive to be somewhat lighter than an equivalent diesel-electric, useful on some lightly-laid WR secondary routes.

In service the Hymeks worked a wide range of WR duties: express passenger services on the routes from Paddington to the West of England where they were paired with the larger Westerns and Warships on the heaviest trains, secondary expresses to South Wales and the Midlands, and freight and parcels work across the WR network. Their 90 mph maximum speed made them suitable for passenger working as well as freight. BR's decision in the late 1960s to standardise on diesel-electric transmission rendered the entire WR hydraulic fleet redundant; all Hymeks were withdrawn by 1975. Four are preserved.