The British Rail Class 313 is a dual-voltage electric multiple unit (EMU) train built by British Rail Engineering Limited's Holgate Road carriage works between February 1976 and April 1977. They were the first production units that were derived from British Rail's 1971 prototype suburban EMU design which, as the BREL 1972 family, eventually encompassed 755 vehicles over five production classes (313, 314, 315, 507 and 508). They were the first second-generation EMUs to be constructed for British Rail and the first British Rail units with both a pantograph for 25 kV 50 Hz AC overhead lines and contact shoe equipment for 750 V DC third rail supply. They were, additionally, the first units in Britain to employ multi-function automatic Tightlock couplers, which include electrical and pneumatic