In 1935, the 4.1200s essentially provide commuter services at the head of push-pull trains composed of five to nine cars, up to 420 tons gross. They are assigned in part to depots of , Mitry, Beaumont ... They are found between Paris on the one hand and Ermont, Creil and Pontoise on the other. In addition to the commuter traffic, 4.1200's also take charge of the freight service between Persian-Beaumont and Luzarches with reversal at Montsoult.
