Automatische Übersetzung. Originaltext in: EN - Original anzeigen The 231 PO 3501 - 3590 series consisted of high-speed Pacific-type (4-6-2) steam locomotives built for the Compagnie du chemin de fer de Paris à Orléans (PO). Designed for express passenger services, these locomotives played a key role in improving journey times and hauling heavier trains on the company’s main lines during the early 20th century.

Ordered in 1909, the series was intended to meet growing demands for faster and heavier express trains on routes with moderate gradients, most notably Paris - Bordeaux and Bordeaux - Irun. The locomotives were closely inspired by the earlier 231 PO 4501 - 4600 class, which had been developed for more mountainous routes. The principal distinction lay in the larger driving wheels, allowing for higher maximum speeds at the expense of tractive effort on steep profiles.

Production of the class was spread across several French manufacturers and delivered in successive batches:
231 PO 3501 - 3520 – built by Société Alsacienne de Constructions Mécaniques (SACM) in 1909, originally without superheating;
231 PO 3521 - 3550 – built by Compagnie de Fives-Lille in 1910;
231 PO 3551 - 3570 – built by Société Alsacienne de Constructions Mécaniques (SACM) in 1912;
231 PO 3571 - 3590 – built by Cail in 1914.