MA 51

The MA 51 rolling stock was a result of research conducted by the Compagnie du chemin de fer métropolitain de Paris (CMP) and the Régie Autonome des Transports Parisiens (RATP) during the 1940 in response to the then-used Sprague-Thomson rolling stock being considered heavy and outdated.

The company envisioned a rolling stock that was lighter and equipped with a Jeumon-Heidmann (JH) system[clarification needed] that had been used on the Sceaux Line since 1938.

The most-used solution at the time was a rolling stock with a common bogie between two cars[clarification needed].

It was equipped with a modulated pneumatic braking system that was judged acceptable in 1952 but later declared outdated in the 1960s.

The RATP lost interest in using only pneumatic braking on cars and as a result the MP 51 was put in service.

Because the métro network still contained many Sprague-model stock in 1974, the RATP decided not to eliminate the MA but instead to modernize it and use it on a line experiencing only light traffic.

Unable to accommodate autopilot and equipped with brakes that were too delicate on iron tracks, the MA's replacement with newer-model rolling stock became inevitable.