Between 1961 and 1964, a total of forty such locomotives were constructed, all of which were built at Doncaster. Design The Class 85 is an AC electric locomotive intended for express services on the West Coast Main Line. Its design bore considerable similarities to the earlier British Rail Class 81, particularly in terms of their shared AEI-supplied equipment. One key area of difference was its adoption of semiconductor-based rectifiers and a rheostatic braking system; the latter was viewed as likely to generate considerable cost savings in comparison to conventional braking by reducing wheel wear. A small proportion of the locomotive's equipment, such as the bogies, were designed by the French industrial group Alstom. In order to achieve the minimal weight requirement stipulated by BR, while still maintaining sufficient structural strength, the lower halves of the body sides were merged into the locomotive's underframe, while the roof and sides above the base of the windows were built from a relatively light steel frame with an aluminium covering. The underframe is a welded steel assembly divided into seven box-like sections, while the bogie frame is built from rolled steel members that were welded together. On the outer faces of the underframe, the coupler and oleo-pneumatic buffers were fitted. 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. Much of the weight was carried by two sets of four spring-loaded side-bearers, which used rubber brushes wherever practical to eliminate the need for lubrication. 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. The bulk of the equipment was installed within two compartments, one containing the rectifier apparatus and the other accommodated the main transformer and associated equipment, while a walkway spanned the length of the power compartment for access purposes. Above the transformer was its roof-mounted radiator and cooling fans, while the braking resistors and motor contactor panel were positioned close by. 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. Power was delivered to the locomotive via overhead catenary, which