The British Rail Class 304 (Originally classed as AM4) were AC electric multiple units designed and produced at British Rail's (BR) Wolverton Works.
The Class 304 was produced for BR's new electric suburban services, enabled by the first phases of the West Coast Main Line electrification between Crewe and Manchester/Liverpool/Rugby. The units conformed to the 1959-design for alternating current (AC) electrical multiple units, and were externally very similar to the Class 305, Class 308 and the 1,200 V direct current (DC) Class 504 units.
Following their introduction during the early 1960s, the Class 304 could be found in operation across the southern and Midland section of the West Coast Main Line. Midway through their service life, the units were reclassified as the Class 304 under the TOPS numbering system. The fleet was withdrawn from service during the early to mid 90s, largely due to the arrival of cascaded rolling stock such as the Class 305/2 units and new Class 323 units. Despite efforts to do so, no units survived into preservation, all examples being eventually scrapped.
Production
The first fifteen units were delivered to Longsight Depot, Manchester from April 1960 as four-car sets, and were originally numbered 001-015. Built by British Rail's Wolverton Works, these units were an aesthetic improvement over the AM2 (Class 302) units previously built at York and Doncaster; they featured a new design cab end with a raked back upper area, following a Design Panel recommendation, and emerged in Multiple Unit Green livery, lined out with yellow. Having been immediately preceded on the Wolverton production line by the two-car 1,200 V DC Class 504 units, a considerably high number of design features were shared between the Class 504 and the first AM4 units.
During 1961, production of a further twenty units followed, numbered 016-035, and intended for the Crewe-Liverpool service which commenced on New Year's Day 1962, although as this local service only required three or four units daily they were principally used elsewhere, for services around Manchester and Birmingham. These units differed from the first batch by having a slightly different body design, with wide saloon windows replacing the narrow compartment-style windows. The Motor Brake vehicles had a different internal layout, with 72 second class seats in saloon layout. This improved layout was adopted for the final batch of AM4s, as well as later batches of AM5 (Class 305) and AM8 (Class 308) units.
The third and final batch of AM4 was another ten units, numbered 036-045, which were almost identical to the second batch and intended for use on the Crewe-Stafford section.
Design
The Class 304 was an interurban electric multiple unit (EMU) train. Its design, which was principally devised to fulfil various requirements laid out by the British Transport Commission, was produced by a team headed by Chief Electrical Engineer S. B. Warder and Chief Mechanical Engineer I. F. Harrison. The units were arranged into four-car sets, consisting of: a Driving Trailer Brake Open vehicle with 82 second class seats (saloon) and a Guard's compartment; a Trailer Composite with 19 first class seats (compartment) and 60 second class seats (saloon), and two toilets; a Motor Brake with 96 second class seats (compartment) and a Guard's compartment; a Driving Trailer with 82 second class seats (saloon), two toilets, and battery equipment. One result of the Motor Brake vehicle having a compartment design was that the window layout on all vehicles was designed to suit, having a narrow window either side of each door.
The body of the vehicle was constructed principally of welded steel. While 16-gauge sheet sections were used for areas such as the bodysides, ends, and roof panels, thinner sections were used in a minority of areas. On some units, fiberglass was inserted into the interior spaces present in the sides, roof, and ends, to provide both thermal insulation and soundproofing; on other units, asbestos was used instead. Additional insulation was sometimes installed beneath the floor panels and the corrugated aluminium floor plate. While much of the passenger compartment's interior finishing was a mixture of timber and plastic, light alloys were used for several elements, such as the doors and luggage racks.