BR Class 81

The BR Class 81 locomotives, originally designated AL1 under the pre-TOPS classification system, were the first of five classes of 25 kV AC Bo-Bo electric locomotives ordered for the electrification of the West Coast Main Line in the late 1950s. Twenty-five were built between 1959 and 1964 by AEI (Associated Electrical Industries) at their Birmingham works, with mechanical parts by Beyer Peacock of Manchester, and entered service on the newly-electrified Styal and Crewe routes from 1960 onwards.

The AL1 to AL5 classes (later Class 81 to 85) represented a major technological commitment by British Railways to the 25 kV 50 Hz AC overhead electrification system that had been adopted as the future standard for BR's principal main lines. The Class 81 used mercury-arc rectifiers to convert the AC overhead supply to DC for the traction motors — technology that was reliable but complex and would later be replaced by silicon rectifiers in successive versions. The locomotives were rated at 3,200 hp and capable of 100 mph, designed to haul the express passenger trains on the West Coast route between London Euston, Birmingham, Manchester, and Liverpool.

The Class 81s gave over two decades of service before being withdrawn between 1989 and 1991 as the newer Class 86 and 87 locomotives took over the principal workings. All twenty-five were scrapped; 81002 was nominally allocated to the National Railway Museum for preservation but was ultimately not retained and was scrapped in the 2000s. The class is unrepresented in preservation.