The PLM assigned four-cylinder compound locomotives with a 4-4-0 wheel arrangement to class C, of which the numbers 61 to 180 were also called “heavy C”. They had air cutters on the smokebox, chimney, Belpaire firebox and cab, hence the nickname “Coupe-Vents”. They pulled the most important express trains and could travel continuously at 90 km/h with 300 tonnes. Only when two coupled axles were no longer sufficient for the heavier trains were they initially replaced by locomotives with a 4-6-0 wheel arrangement on hilly routes and soon had to pull slower trains as well. Although the locomotives were retired between 1929 and 1936, they formally received new numbers when the SNCF was founded in 1938.

For fast freight trains on the line through the Cevennes, the PLM opted for the 4-8-0 wheel arrangement, which still allowed a large boiler with a low axle load and good curve guidance. The only problem was the narrow firebox, which was offset by making it relatively long. They could tow 1,618 tonnes on the flat at 40 km/h and 501 tonnes on a one percent incline at the same speed. From 1919 more than 200 locomotives received a superheater and the four-cylinder compound engine was replaced with a simple one. They also pulled heavy passenger trains when needed and were in use until 1952.

In 1909, the PLM started comparisons with Pacfic locomotives with different types of power plants. 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 single 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. Based on the De Glehn principle, both groups of cylinders each had their own valve gear. The high-pressure cylinders acted on the second coupled axle and the low-pressure cylinders on the first.

No. 6013 on a postcard

Henri Fohanno

During the tests, the 6001 already showed that it could bring a 495-tonne train to its destination in just 87 minutes over a 160 km long route with an altitude difference of more than 300 meters. 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 examples came from the works on the Loire in Nantes and in 1921 another 25 from SACM. 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 series locomotives were collectively referred to as 231 C. In the SNCF they were then renamed 5-231 C with the appropriate regional prefix.

The PLM operated some main routes on which important express trains with high passenger numbers had to be transported. One of these was the north-south connection from Calais to the Riviera, on which the “Train Bleu” ran with many passengers from Great Britain. Since the Pacifics were not sufficient there, one of the first Mountain locomotives in Europe was developed in 1925 with the 241 A 1. Their requirement program stipulated that they should be able to pull 600-ton express trains at 110 km/h on the flat and at 75 to 80 km/h on the route between Laroche and Dijon with gradients of 0.4 to 0.8 percent.

As a compound locomotive based on the De Glehn design, the low-pressure cylinders were on the outside at the height of the bogie, while the inner high-pressure cylinders were moved further to the rear. They drove the first and second coupled axle, which led to very short connecting rods. The bogie had a play of 61 mm to each side, the second coupled axle had wheel flanges weakened by 21 mm, the third coupled axle could be shifted 21 mm to each side and the trailing axle was an Adams axle which was radially adjustable by 96 mm to each side. The smoke box door was cone-shaped for better streamlining.

After the prototype there were the production engines No. 2 to 80 also from Schneider, the 81 to 95 from Marine et d'Homécourt, the 96 to 115 again from Schneider and finally two more deliveries from Marine et d'Homécourt, with the numbers 116 to 125 and 126 to 145. The boiler dimensions of the production engines had been changed slightly, the superheater had even been reduced from 105 to 86 m². A boiler output of 2,180 hp was calculated for a journey with a 625-tonne express train on the route between Laroche and Blaisy-Blas. Even with an 850-tonne express train, it was still possible to reach 70 km/h at 0.5 percent.

From 1932 a total of 48 of the 145 locomotives were rebuilt by André Chapelon to achieve higher efficiency and greater power. He increased the diameter of the connecting pipes between the high and low pressure cylinders and installed a double Kylchap exhaust system. In addition, large smoke deflectors were fitted and the cone-shaped smokebox door replaced with a flat one. The locomotives converted in this way were classified as 241 D, with the running numbers being retained. At SNCF, the two classes became the 5-241 A and 5-241 D.

The 242 AT was the first of four series of 4-8-4T tank locomotives that the PLM had built to accelerate the suburban trains that departed from the Gare de Lyon in Paris. They replaced the tank locomotives 232 AT and 232 BT. A total of three manufacturers delivered 120 locomotives between 1926 and 1929.

They had a Belpaire firebox with a steeply sloped grate between the wheels of the third and fourth driving axles. Power was transmitted via four compound cylinders of the de Glehn system. Over the years it often became apparent that the frames were too weak for the long wheelbase.

They were classified by the SNCF as 5-242 TA. After the war, they were distributed across several regions and received region-specific adjustments, for example wind deflectors. They were decommissioned by 1968.