[1] The locomotive was developed as a part of the programme of works to electrify the West Coast Main Line during the late 1950s and early 1960s.

During the late 1950s, British Rail (BR) embarked upon the electrification of the West Coast Main Line, a strategy which necessitated the procurement of a large number of electric locomotives to utilise the newly-installed infrastructure.

[1] Its design bore considerable similarities to the earlier British Rail Class 81, particularly in terms of their shared AEI-supplied equipment.

[1] The locomotive was seated upon each bogie via a double-ended rubber cone-shaped pivot, the alignment of which was defined by a transverse spring anchorage.

[1] The Class 85 featured a sizeable power compartment, of which particular attention was paid to making it as accessible for maintenance purposes as was realistically possible.

Above the transformer was its roof-mounted radiator and cooling fans, while the braking resistors and motor contactor panel were positioned close by.

[1] In between the transformer unit and the rear bulkhead was the brake compressor, primary air reservoir, and the fault indicator panel.

On the opposite side of the power compartment, next to the forward bulkhead, was the auxiliary compressor, battery charging apparatus, and a chemical toilet for the locomotive crew.

[1] The driving controls, which conformed to BR's standard conventions of the era, were mounted on a sloped plastic-covered desk directly beneath the forward window; various instruments, light switches, indicators, and gauges lined the centre console.

[1] Upon their entry to service, the AL5 fleet was used to haul express trains on the then newly electrified West Coast Main Line, from Birmingham, to Crewe, Manchester Piccadilly, Liverpool, and later Preston.