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Parisiens (RATP) during the 1940 in response to the then-used Sprague-Thomson rolling stock being considered heavy and outdated.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. In addition, the company hoped to improve braking. The most-used solution at the time was a rolling stock with a common bogie between two cars[clarification needed].
At the same time, the company also desired to have circulating modular trains so that they may have been expanded during peak hours. Lines equipped with stations of at least 75 metres (82 yd) supported trains with two trainsets and those with stations of at least 105 metres (115 yd) supported trains with three trainsets. An extension of stations to 105 metres (115 yd) that began in 1931 was never completed.
Each trainset consisted of three body sections resting on four bogies. The central section was shorter than the rest and in 1952 was designated as a first class car. The trainset were equipped with Scharfenbergautomatic couplings allowing for quick coupling and uncoupling of trainsets.
Seats were divided into two classes, and fluorescent lighting was used. Folding seats were used at each end to increase the number of seats for passengers.
Initially, the livery was grayish-blue across all cars, however with the introduction of first class in the 1950s[clarification needed], the RATP piloted first class cars in the middle colored red, however this did not catch on. RATP eventually incorporated yellow into the color scheme, between gray and blue bands. The livery on second class cars was gray and blue and was yellow on first class cars.
The model is unusual in that the driving cab could double as passenger accommodation. A door existed which, when opened, allowed access to the control panel. A folding seat was attached to the side of the door, allowing for the conductor to be seated. When the door was closed, it hid the control panel allowing for additional space for passengers.