In 1929, André Chapelon used all the knowledge he had acquired up to this point to fundamentally rebuild Paris-Orléans Pacific No. 3566, built in 1912. The result was almost twice the power with the same coal consumption. Because of this success, the 3501 to 3520 series locomotives were also rebuilt in 1932. Ten more followed in 1934.

The measures included thicker steam pipes, thermic siphons, a new valve gear and an increase in superheating from around 300 to 410 degrees Celsius. In addition, an ACFI feedwater heater and a double Kylchap blast pipe were installed.

The indicated power achieved through the rebuild was up to 3,700 hp for a short time or 2,800 hp permanently on the draw bar. The maximum speed of 120 km/h (75 mph) permitted by the PO could be maintained permanently with an express train weighing more than 650 tonnes on gradients of 0.3 percent. Accordingly, test runs on a topographically demanding line resulted in an average speed of 115 km/h, since the speed never dropped significantly.

These successes also brought the Nord and the Est to order the same locomotives. A total of about 100 locomotives were created, which were either rebuilt from old ones or built from scratch. These all came from the PO works in Tours and were therefore called “Reines de Tours” (Queens of Tours). When the SNCF was founded, the locomotives were assigned to the 4-231 F series. They were last used in 1967.

The ten-wheelers with the numbers 4201 to 4370 were built for the Paris-Orléans from 1915 onwards for express, passenger and freight trains. During the First World War, some of the locomotives were built by North British in Scotland and a total of 170 had been built by 1922. They shared the boiler and cylinders with other ten-wheelers and with the 2-8-2T tank locomotives of the series 5301.

In 1924 and 1925, 21 were sold to Morocco. From 1929 onwards, the remaining ones received smoke deflectors after tests by André Chapelon. When the SNCF was founded in 1938, the locomotives that came directly from the PO were given the designation 230 G and those that had since gone to the État were given the designation 230 K. In 1947 and 1948, 14 locomotives that were used in wooded areas got oil firing. They were retired until 1970 and the 230 G 352 and 353 are still preserved today. The 353 could be seen in many films since the seventies.

Around 1905, the PO was looking for more powerful express locomotives, since the existing 4-6-0 locomotives of series 4001 to 4084 had reached their limits. The solution was the 4-6-2 wheel arrangement, also known as “Pacific”. This was the first Pacific in Europe to be used on main lines.

No. 4546 built by ALCO at the Cité du Train in Mulhouse

Hugh Llewelyn

With the additional trailing axle, it was possible to install a larger firebox with a grate area of more than four square meters. In order not to shift the center of gravity too far back and thus away from the driving axles, the firebox had a trapezoidal layout. Since the front part was narrower, it could be drawn in between the wheels of the rear driving axle. Additionally, the firebox was of the Belpaire type to create a larger direct heating surface. 

View of the boiler with the special shape of the firebox

Railway and Locomotive Engineering, September 1908

The power plant was of the Du Bousquet-De Glehn type, i.e. a four-cylinder compound engine with outer high-pressure cylinders that acted on the second driving axle and inner low-pressure cylinders that acted on the first driving axle. The driving wheels had a diameter of only 1,850 mm in order to be able to maintain a high average speed even on hilly routes. This was primarily the line from Limoges to Toulouse, which had gradients of up to 1.05 percent. Later, the locomotives with the numbers 3501 to 3589 were developed, in which the driving wheels were 10 cm larger and intended for flatter lines.

The first 40 examples were built by SACM and Hanomag from 1907 and still worked with saturated steam. On the relatively flat line between Paris and Les Aubrais, they reached an average speed of 88 to 95 km/h with a trailing load of 360 tonnes. From 1908, 30 other very similar locomotives were built by ALCO in the USA. From 1910, the last 30 that were made by the SFCM followed. From the factory they had a superheater and an enlarged diameter for the high-pressure cylinders.

Between 1932 and 1934, André Chapelon rebuilt twelve locomotives to numbers 4701 to 4712, which had a 4-8-0 wheel arrangement and delivered more than 4,000 hp. Another 25 4-8-0 locomotives followed in 1940 and 1941, which the SNCF designated as 240 P 1 to 25. The non-rebuilt locomotives received innovations such as Kylchap exhaust systems, superheaters, feedwater heaters or smoke deflectors during their service life. They became the 4-231 A 501 to 600 on the SNCF and were retired by 1954.

In 1911, the PO ordered 2-8-2T tank locomotives from SLM in Switzerland for the transport of freight trains, but also passenger trains, on the steep lines in the Massif Central. They were based on a locomotive that had already been built for the Thunerseebahn in 1908. Further batches were supplied by French manufacturers and North British.

A special feature for locomotives with this wheel arrangement was the drive on the second coupled axle. In order to be able to run through small curve radii, the first and last driving axles were combined with the neighboring carrying axle to form a Zara bogie. This resulted in a fixed wheelbase of just 1,500 mm. The blastpipe consisted of a variable cone and a three-fold cloverleaf nozzle.

They were able to pull a 200-tonne train at 30 km/h on a 3.5 percent ramp. On the flat they reached their top speed of 70 km/h with up to 1,500 tonnes. The special shape of the coal bunker earned the locomotives the nickname “boat butt”.

Between 1924 and 1929, 31 locomotives were transferred to Morocco. The PO rebuilt all of its locomotives to a Kylchap exhaust system. Some later received Worthington feed water heaters, and most of them also had their boiler pressure increased to 13 bars. At the SNCF they were also used far away from the Massif Central and were designated 4-141 TA. The last machine was retired in May 1970.

Beginning in 1909, the Paris-Orléans procured a series of 2-10-0 freight locomotives which had been developed from the Pacific express locomotives of the series 4501 to 4600. The four-cylinder compound engine was also adopted from these, which ensured exceptional performance when used in a heavy freight locomotive. The boiler could not be taken over unchanged because the firebox would not have fitted completely between the coupling wheels. However, the slightly shorter boiler also has a trapezoidal firebox, which in this case starts above the fifth coupled axle and then tapers to fit with the lower front end between the wheels of the fourth coupled axle. 

Schematical drawing with dimensions

Locomotive Magazine, October 1910

They were stationed around the Massif Central and hauled freight trains of up to 1,200 tonnes. The performance profile still permitted around 750 tonnes at 20 km/h on a gradient of one percent. Although they were not actually designed for this role, they even pulled express trains on the demanding mountain routes. A total of 70 examples were built in three batches by different manufacturers until 1913. Initially, small two-axle models were used as tenders, which offered space for just twelve cubic meters of water and weighed less than 30 tonnes when loaded. Apparently, this had been considered sufficient, since there was no need to run long distances non-stop. In the second and third series, three-axle tenders with a water capacity of 20 cubic meters were used.

The 150 6065 is now standing at a roundabout in Coulounieix-Chamiers

Père Igor

The first production locomoties were not without problems, but with the exception of the occasional overheated axle bearing, all problems could be eliminated. They were later modernized, starting with cloverleaf-shaped blast pipes in the 1920s. From 1929, eleven engines were fitted with even more efficient Kylchap induced draft systems, which reduced consumption, and from 1930 a total of 30 units were fitted with different superheaters. André Chapelon used one locomotive as the basis for his six-cylinder locomotive 160 A 1. When the SNCF was founded, the remaining engines were redesignated as the 4-150 A 1 to 70. As early as 1940, the electrification of some routes in the Massif Central meant that these steam locomotives were no longer needed there and were relocated. After the Second World War, despite their age, the locomotives continued to be an important item on the non-electrified routes due to the lack of alternatives. The last example was finally retired in 1955 after the engines had been replaced by diesel locomotives.