British Rail Class 20

English Electric Type 1 British Rail Class 20
Hunslet-Barclay 20903 on a weedkilling train at Doncaster, April 1994
Type and origin Power type Diesel-electric Builder English Electric at Vulcan Foundry and Robert Stephenson and Hawthorns Build date 1957–1962, 1966–1968
Specifications Configuration: ​  • Whyte Bo-Bo  • UIC Bo'Bo' Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Wheel diameter 3 ft 7 in (1.092 m) Minimum curve 3.5 chains (70 m) Wheelbase 32 ft 6 in (9.91 m) Length 46 ft 9+1⁄2 in (14.262 m) Width 8 ft 9 in (2.67 m) Height 12 ft 8 in (3.86 m) Loco weight 72 long tons (73.2 t) Fuel capacity 380 imp gal (1,700 L; 460 US gal) Prime mover English Electric 8 SVT Mk.II Traction motors D8000–D8049: EE 526/5D Remainder: EE 526/8D Transmission DC generator, DC traction motors MU working ★ Blue Star Train heating None Train brakes Vacuum
Performance figures Top speed 75 mph (121 km/h) Power output Engine: 1,000 hp (746 kW) Tractive effort Maximum: 42,000 lbf (186.8 kN) Brakeforce 35 long tons-force (349 kN)
Career Railroad(s) British Railways Number D8000–D8199, D8300–D8327; later 20001–20228 Axle load class Route availability 5

The British Rail Class 20, originally known as an English Electric Type 1, was a class of diesel electric locomotive. 228 locomotives in the class were built by English Electric between 1957 and 1968. The large number was partly to do with the failure of other early designs in the same power range, and reliable locomotives being needed.

The locomotives were originally numbered D8000–D8199 and D8300–D8327. They are known by railway enthusiasts as "Choppers", a name taken from the distinctive beat the engine produces under load which resembles the sound of a helicopter.