After Victor Forquenot had created his first 2-4-2 express locomotives by adding a trailing axle to his 2-4-0, he ordered new locomotives of this wheel arrangement to be built in 1876. They were designed for lines with inclines of 1 to 1.6 percent and curves with a radius between 300 and 500 metres. Driver diameter was 2,000 mm with the shortest possible wheelbase of 2,100 mm. To increase running stability, the coupling between the locomotive and tender was tightened with springs.

Production was carried out in a total of five places between 1876 and 1884. With 56 locomotives, SACM built the most. 20 each came from the PO's workshops at Tours, from Sharp, Stewart & Co. and from Saint-Léonard. Only ten were delivered from Carels. This resulted in a total of 126, which were numbered 265 to 390. No. 331 was later used to test the Durant and Lencauchez valve gear. Some passed on to the SNCF as 121 A, the last ones were used until the end of World War II.