The British Rail Class 71: Britain’s Forgotten High-Power Electric Locomotive. The British Rail Class 71 was one of the most powerful and charismatic electric locomotives ever to run in Britain. Introduced in the late 1950s, these 750V DC giants hauled heavy express passenger and freight trains across the Southern Region, particularly through Kent. Nicknamed “Roarers” for the unforgettable sound of their traction motors, the Class 71s were engineering muscle in motion — delivering immense power