Overview
The British Rail Class 46 was a fleet of diesel‑electric locomotives built between 1961 and 1963 at Derby Works as part of British Rail's early diesel modernisation programme. Fifty‑six machines were constructed and originally carried the numbers D138–D193. With the introduction of the TOPS computer classification the series became known generally as Class 46. They were used in mixed‑traffic roles, handling long‑distance passenger trains, regional services and secondary freight duties through the 1960s and 1970s.
Design and technical features
The Class 46 shared its overall structural design and the same Sulzer prime mover as the closely related Class 45. The principal distinguishing feature was the choice of electrical equipment: Class 46 locomotives were fitted with Brush generators and traction motors, whereas the Class 45 used Crompton Parkinson electrical gear. This change affected maintenance practices, parts supply and some performance characteristics, but broadly the two classes performed to similar duties.
Production and numbering
Built at Derby Works, the locomotives carried sequential numbers on delivery and were later renumbered under the TOPS system. The relatively small production run reflected British Railways' policy at the time of building several related families of diesels with shared mechanical components but differing electrical fitments supplied by competing manufacturers.
Service history and withdrawal
Throughout the 1960s and early 1970s the class provided reliable service on a wide range of routes. As newer locomotive types arrived, operational needs changed, and electrification of main lines progressed, the role of the Class 46 diminished. The first withdrawals began in the late 1970s, and the last examples were retired from British Rail service by 1984. The differing electrical equipment and the availability of more modern units contributed to their relatively early withdrawal.
Characteristics
- Builder: Derby Works (British Rail)
- Years built: 1961–1963
- Number built: 56 (originally numbered D138–D193)
- Prime mover: Sulzer diesel engine with diesel‑electric transmission
- Electrical equipment: Brush generator and traction motors (distinct from Class 45)
- Classification: Renumbered under TOPS as Class 46
Legacy and further reading
The Class 46 illustrates how British Rail adopted common mechanical designs while testing competing electrical systems from different suppliers, in this case Brush equipment rather than Crompton Parkinson. The class is of interest to students of mid‑20th century British diesel traction and to railway enthusiasts documenting the transition from steam to modern traction. For more general context on diesel traction and technical developments see introductory material on diesel locomotives and supplier histories such as accounts of Brush. Comparative material and fleet histories for related designs can be found in sources covering the Class 45 and other contemporary types.