class-42-warship

The BR Class 42 'Warship' was a series of 33 diesel-hydraulic B-B locomotives built by BR Swindon Works between 1958 and 1961 for the Western Region, named after Royal Navy warships and forming part of the Western Region's distinctive diesel-hydraulic fleet that used hydraulic rather than electric transmission — a choice that differentiated the WR from all other BR regions and reflected the GWR/WR's tradition of technical independence from mainstream BR practice. A related but separate batch of five locomotives was built by North British Locomotive Co. and designated Class 43.

The Warship class used twin Maybach MD650 diesel engines (later some re-engined with Paxman Ventura engines) driving through the Mekydro K184U hydraulic transmission — a German-designed system in which the engine power was transmitted to the wheels via a fluid torque converter and hydraulic gearbox rather than the diesel-generator-traction-motor chain of diesel-electric practice. The hydraulic transmission's theoretical advantages — lighter weight, smoother power delivery at all speeds, faster response to throttle changes — were appealing on paper, but in practice the hydraulic components required more specialised maintenance than the more robust diesel-electric alternatives, and the Warship's overall availability was lower than comparable diesel-electric types.

Two examples are preserved: D821 Greyhound and D832 Onslaught.