British Rail Class 85

The BR Class 85, originally designated AL5, was the fifth and final class of the West Coast Main Line AC electric evaluation fleet, comprising forty Bo-Bo locomotives built between 1961 and 1964 by BR at Doncaster Works with electrical equipment by AEI (Associated Electrical Industries). The AL5 completed the five-manufacturer evaluation programme that also produced the Classes 81–84, in which British Railways awarded identical contracts to five different manufacturers — AEI, Metropolitan-Vickers, English Electric, North British/GEC, and Beyer Peacock/Brush — to allow comparative assessment of different AC traction electrical systems before committing to a production standard.

The Class 85 used AEI's silicon rectifier technology for the AC–DC conversion — a significant advance over the mercury-arc rectifiers used in the Class 81 (AEI's other WCML class) and the other early AL classes. Silicon rectifiers were more compact, lighter, and required less maintenance than mercury-arc equipment, and the Class 85 demonstrated in service that they were also more reliable. The lessons learned from the Class 85's silicon rectifier installation directly influenced the design of the Class 86, the first production WCML electric, which adopted silicon rectifiers as standard.

The forty locomotives entered service from 1961 on the newly-electrified WCML sections, working express passenger and mixed traffic duties from London Euston to Birmingham, Manchester, and Liverpool. They were rated at 3,200 hp, consistent with the other AL classes, and capable of 100 mph. In service the Class 85 proved more reliable than several of its AL contemporaries, a performance attributed to the advantages of the silicon rectifier over earlier technology.

Withdrawal of the Class 85s began in 1989 as the more powerful and modern Class 90 locomotives arrived on the WCML, and the last examples were retired in 1991. None was formally preserved, though 85006 was retained at Crewe for a period as a potential museum exhibit before being scrapped. The Class 85 is therefore unrepresented in preservation, despite its historical significance as the class that demonstrated silicon rectifier technology and directly influenced the Class 86 production design.