The X 900 was a type of light diesel railcar developed by Établissements Billard for the Compagnie de chemins de fer départementaux in the forties. Its manufacturer designated it A 75 D. It had two axles, one of which was powered by an 80-hp diesel engine mounted transversely on one end. Cabs were on both ends. The interior had 32 seats and additional space for 25 standing passengers. Luggage could be stored in a rack on the roof.

Only the first five were built by Billard at Tours between 1946 and 1949. Eleven more were built by the CFE's own shops at Montmirail between 1948 and 1953. Later the power was increased to 100 hp. But two lost their engine and were now used as trailers. The last ones were withdrawn from passenger service in 1968. After that, some were used as inspection vehicles. Five have been preserved, three of which are being owned by the Chemin de fer touristique de la Sarthe.