Although the FCSF usually designated passenger locomotives with odd numbers, the class XII designated a series of 30 metre-gauge Pacific locomotives. ALCO-Cooke built the first batch of 20 in 1919 and the second batch of ten in 1921. They were formally designed only for passenger service, but in reality they were not only used for passenger and mixed trains, but also for pure freight trains and for switching. With the progression of electrification and dieselization, their area of service changed multiple times. Their withdrawals followed in the seventies.