The British Rail Class 308 alternating current (AC) electric multiple units (EMU) were built by British Railways' Holgate Road carriage works in three batches between 1959 and 1961. They were initially classified as AM8 units before the introduction of TOPS. Description Class 308/1 The first batch of 33 units were built in 1959, classified as AM8 and numbered 133–165. This was later changed to Class 308/1 under the TOPS system, and units were renumbered 308133–165. These units were built to operate commuter services on the Great Eastern Main Line (GEML) from to , , , and . Each unit was formed of four carriages: two outer driving trailers, an intermediate trailer, and a motor coach. Electrically the Class 308 stock has the same equipment as the Class 302 stock with a few modifications, some of these are the types of overload, the use of fan-cooled rectifier continued until the rectifiers were modified to 8-diode type from 1982. This modified main rectifier was also modified and used on the Class 309 stock due to the problems of fan-cooled types suffering from blocked filters causing failures in traffic. The braking system is basically the same as the Class 302 stock with the exception of the motor coach retaining the cylinder rather than the as fitted to Class 302 after replacing the cast-iron brake blocks with composite (Ferodo) type. From 1981 to 1983, the units were refurbished, which included opening out compartments, fitting of gangways between carriages, and moving first class seating from the intermediate trailer to one of the driving trailers, with the same problems as the Class 302 stock of having first class passengers sitting above the Westinghouse CM38 compressor, however the Gresley bogies being retained. In this modified form, the technical description of the formation was BDTCOL+MBSO+TSOL+DTSO. Individual carriages were numbered as follows: 75878-75886 and 75896-75919 - BDTCOL 61883-61915 - MBSO 70611-70643 - TSOL 75887-75895 and 75929-75952 - DTSO Class 308/2 A second batch of nine units, numbered 313–321, were built for boat train services on the London, Tilbury and Southend line in 1959–60, from London Fenchurch Street to . These units were later reclassified as Class 308/2 under TOPS. Each unit was formed of four carriages: two outer driving trailers, an intermediate trailer, and a motor luggage van, with the reduction in luggage some MLV's were converted at Swindon Works with a different seating arrangement to the original passenger