British Rail Class 41 (Warship Class)

British Rail Class 41
D600 'Active' at Reading in 1959
Type and origin Power type Diesel-hydraulic Builder North British Locomotive Co. Serial number 27660–27664 Build date 1958–1959 Total produced 5
Specifications Configuration: ​  • UIC (A1A)(A1A)  • Commonwealth A1A-A1A Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Wheel diameter Driving: 3 ft 7 in (1.092 m) Idling: 3 ft 3 1⁄2 in (1.003 m) Wheelbase 50 ft 0 in (15.24 m) Length 65 ft 0 in (19.81 m) Width 8 ft 8 in (2.64 m) Height 12 ft 10 in (3.91 m) Loco weight 117 long tons (119 t; 131 short tons) Fuel capacity 800 imp gal (3,600 l; 960 US gal) Prime mover NBL-MAN L12V 18/21S, 2 off Engine type V12 Diesel Transmission Hydraulic, Voith L306r MU working ■ Orange Square Train heating Steam Train brakes Vacuum
Performance figures Maximum speed 90 mph (145 km/h) Power output Engines: 1,000 bhp (746 kW) × 2 Tractive effort Maximum: 50,000 lbf (222 kN) Continuous: 39,600 lbf (176 kN) Brakeforce 88 long tons-force (877 kN)
Career Operators British Railways Numbers D600–D604 Nicknames "Warships” Axle load class Route availability Retired December 1967 Disposition All scrapped

The British Railways Class 41 diesel-hydraulic locomotives were built by the North British Locomotive Company in Glasgow during 1957 and 1958. Although they were withdrawn before TOPS was introduced, British Rail classified them as Class 41. All were named after Royal Navy vessels, hence the nameplates each bore a subtitle "Warship Class".

The fleet was ordered by the British Transport Commission as direct comparison with British Rail Class 40, and were not actually wanted by the Western Region, who preferred their production fleet of D800 Warships. The D600s were the result of power politics within the BTC and the WR: the former was unwilling to sanction radical, stressed-skin lightweight construction locomotives at the time, while the latter was equally insistent that at least some of the new Type 4 power range locomotives on order be equipped with hydraulic transmission. They were much heavier than production Warships (almost 120 long tons (122 t; 134 short tons) compared to 80 long tons (81.3 t; 89.6 short tons)) and can be regarded as standard 1950s British design diesel locomotives that just happened to contain two lightweight, high-revving diesel engines coupled to hydraulic transmissions rather than one large, slow-revving diesel engine and electrical generator set. For this reason they were practically obsolete in design terms before they had left the drawing board.

Each locomotive was equipped with two MAN L12V18/21A diesel engines, each set to produce 1000 hp (750 kW) at 1445 rpm. This conservative rating was partly because NBL was very inexperienced at constructing diesel locomotives and partly because the Voith L306r three speed transmissions available at the time were not able to accept more. MAN had refined the engine design to produce 1,100 hp (820 kW) at around the time the D600 order was placed with NBL. The A1A-A1A wheel arrangement likewise came about because the BTC-mandated heavyweight construction required 6 axles to keep to a 20-ton axle loading, but NBL could not work out how to create a pivotless bogie and driving arrangement for C-C wheel arrangement. There were no C-C diesel-hydraulic locomotives to use as a template in mid-1955. The arrangement produced a continuous tractive effort of 39,600 lbf (176 kN) at 12.6 mph (20.3 km/h). Unusually for a British diesel locomotive, the D600s had spoked wheels. They could work in multiple with each other or up to two D6300 locomotives using the orange square coupling code.