The British Rail Class 84 was a 25 kV AC electric locomotive that operated on the West Coast Main Line (WCML) of the London Midland Region.

As part of the modernisation of the West Coast Main Line, which included electrification, 100 locomotives of five types were acquired from different manufacturers.

In April 1963 the entire fleet was temporarily taken out of service, and was returned to GEC Dukinfield, the builder of the electrical equipment, in an attempt to find a solution, and remedial work was carried out.

By the mid-1970s, having already spent a substantial amount of money on them, British Rail could not justify any further investment in the fleet, especially since the recently introduced Class 87s allowed them to be sidelined.

[12] 84009 saw further use in a new guise; it passed to the British Rail Research Division, and was rebuilt as an unpowered mobile load bank tester, to test the power supply to new and upgraded overhead line equipment, and was renumbered as ADB968021.