 They replaced and supplemented the 231 B that had a tendency to derail.The class was numbered 231-501 to 231-783 by the "État" and 231.C.501 to 231.C.783 by the SNCF; with class letters "C" through "H" used depending on the level of rebuilding and modernisation.The first locomotives were built by Fives-Lille; however only the first locomotive has entered service before the city of Lille was overrun by the advancing German Army during World War I.