When the class 380 with a 2-10-0 wheel arrangement could no longer cope with the increased weight of the express trains on the Tauern Railway, Gölsdorf had to develop an even more powerful mountain express locomotive. Since the maximum axle load was still limited to 13.8 tonnes, a total of six axles was no longer sufficient. Based on his previous experience with laterally adjustable coupled axles, he dared to develop a twelve-coupled locomotive for the winding mountain route for the first time.
In order to be able to negotiate curves with a radius of 150 meters, the leading axle could be radially adjusted by 50 mm and three of the driving axles could be shifted laterally. The freedom of movement of the second and fifth coupled axle was 26 mm and that of the sixth 40 mm. The third, which was the driving axle, had no wheel flanges. To prevent the coupling rods from jamming in curves, these were connected to the crank pins on the last two axles with cardan joints.
The boiler tapers towards the front and was the largest that had been installed on an Austrian locomotive to date. With the oil firing, this generated an output of 2,020 hp. Express trains weighing 360 tonnes could be pulled at 40 km/h on the Tauern Railway's incline of 2.8 percent. In order to comply with the axle loads, the lightweight construction of the locomotive was taken to the extreme in many places, which later led to problems with durability.
Sectional drawing with dimensions
Die Lokomotive, November 1911
Although the chassis showed good running characteristics on test runs at up to 92 km/h, it was only approved for 60 km/h. However, it remained with a single locomotive, which was taken over by the BBÖ after the First World War and was not built again due to the plans for electrification. It was retired in 1928 after a rupture in one of the inner cylinders. In Württemberg, the otherwise good experience with the locomotive was used as an opportunity to develop the K with the same wheel arrangement.