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.