 They emerged when a class of locomotive was conceived in 1912 that was to handle express and passenger trains in border areas or in shuttle services on short routes.A tank engine design with symmetrical running gear was envisaged because, unlike a tender locomotive, it could run equally fast forwards and backwards and could be operated on return journeys without having to be turned on a turntable.Its power and top speed were to be the same as those of the P 8.