The prototype, LNER No. 6701 was completed at Doncaster Works in 1941 to a design by Sir Nigel Gresley, but electrification of the Woodhead Route together with construction of 69 similar units was delayed by the Second World War. It was tested on the few sections of 1500 V DC lines owned by the LNER but had not worked any great distance by 1947 when it was loaned to Dutch Railways to help with their post war shortage of locomotives. In September 1945 the LNER assigned it the classification EM1; previously it had been unclassified.
In 1950–1953, a further 57 locomotives were built at Gorton locomotive works, Manchester, to a modified design; these were also classified EM1. There were also to have been 24 built at Darlington Works, but these were cancelled. Electrical equipment was supplied by Metropolitan-Vickers, who completed the final assembly of the locomotives at Dukinfield Works. They were later reclassified as Class 76 under the TOPS classification scheme introduced on 28 March 1968.
The locomotives were fitted with twin diamond-shaped pantographs. At certain points on the Woodhead Line, notably in the vicinity of steam locomotive water-columns, the electric overhead lines were as high as 20 feet above the tracks. The pantographs (BR practice utilised both raised in normal Woodhead operation in order to maximise current collection under any weather condition) had to stretch to almost their full height to reach the wires at such points.
Although mainly intended for freight working, the locomotives also regularly worked Woodhead Line passenger services – especially after the sale of the Class 77 locomotives to the Netherlands Railways in 1968. Fourteen locomotives (26020, 26046–26057) being fitted with steam heating apparatus. Thirteen of these gained classical Greek names. The names were removed in 1970 after the discontinuance of passenger services in January of that year.
Seven locomotives of this type were constructed. They represented the first Co-Co type of overhead electric locomotive built for use in the United Kingdom. The design was based on that of the smaller Class EM1, which dated from 1941. Initially, 27 locomotives of this type had been planned, but by the early 1950s, the benefits of using the 25 kV AC system had been demonstrated, which meant that the Woodhead Line would be an isolated electric system. Consequently, the order was cut to just seven locomotives.
The locomotives were initially numbered 27000-27006 and were painted in BR black livery. Construction took place at Gorton Works, Manchester with electrical equipment supplied by Metropolitan-Vickers. All seven were named after characters from Greek mythology in 1959-1960. They were primarily used for express passenger trains between Manchester Piccadilly and Sheffield Victoria. In 1957, the class was renumbered with the addition of an "E" prefix to the number. In the early 1960s, the class started to receive the standard BR green livery. At least one of the class, E27002, received the electric blue livery carried by the AC electric locomotives.
The class was withdrawn en masse in September 1968. They were stored at Bury by BR in the hope of sale to a foreign railway. The passenger service for which the Class 77s were built continued to be operated by Class 76s, until its withdrawal on 5 January 1970. The Woodhead Line was closed as a through route in 1981, leaving just stubs between Manchester Piccadilly and Hadfield in the West and Sheffield Victoria and Deepcar in the East.