Paris-Lyon-Méditerranée No. 6001, 6011 to 6030 and 6221 to 6285

In 1909, the PLM started to compare Pacfic locomotives with different types of engines. The locomotive with the number 6001 had a saturated four-cylinder compound engine and a boiler pressure of 15 bars, while the locomotive initially given the number 6002 was built with a superheated simple four-cylinder engine and a boiler pressure of only 12 bars. Although the compound engine had already emerged as the winner in the first comparisons, series orders of both versions were ordered for more precise comparisons under everyday conditions. While the 6002 was renumbered 6101, the first production examples of the 6001 were numbered 6011 to 6030.

In contrast to practice in Germany, the smaller high-pressure cylinders were arranged on the outside at the height of the second bogie axle. The low-pressure cylinders were inside and below the smoke box. According to the De Glehn principle, both groups of cylinders each had their own valve gear. The high-pressure cylinders acted on the second driving axle and the low-pressure cylinders on the first.

During the tests, the 6001 already showed that it could haul a 495-tonne train over a distance of 160 km with an altitude difference of more than 300 meters in just 87 minutes, what made an average speed of 110 km/h. The 6002 had taken over ten minutes longer to cover the same distance with a slightly lighter train, using more coal. Nevertheless, it was found that the 6001 could have used larger cylinders.

Series production initially started in 1912 with locomotives 6011 to 6030, which were built by Henschel in Germany due to a lack of domestic production capacity. The diameter of the cylinders had been increased from 390 to 440 and from 620 to 650 mm and the cylinders were now all in a line at the height of the smoke box. They were factory built with a superheater and the 6001 was also fitted with a new superheated boiler in 1912.

In 1913 and 1914, 40 more came from the works on the shores of the Loire in Nantes and in 1921 another 25 from SACM in Alsace. The first series was renumbered 6201 to 6220 and the later series locomotives were given the numbers 6221 to 6285. In the PLM's new numbering scheme from 1925, the prototype and production locomotives were collectively referred to as 231 C. In the SNCF they were then renamed 5-231 C with the appropriate regional prefix.