101 Hymek Diesel Hydraulic locomotives were built for BR's Western Region by Beyer Peacock of Gorton, Manchester, the first being handed over in 1961.
Equipped with more powerful engines than earlier diesel locomotives the Hymeks delivered sufficient power to haul express passenger trains singly, but were economical for use on local good trains. They quickly proved themselves to be highly effective replacements for several hundred former GWR 'mixed traffic' steam locomotives and formed the backbone of WR's mixed traffic diesel fleet through the 60's and early 70's.
After a successful career hauling any train the WR ran from principal expresses to pick-up goods and branchline demolition trains, BR decided to standardise on diesel electric traction and the Hymeks were all withdrawn by 1975. Several have survived to operate occasionally on heritage railways.