Prussian T 6

At the beginning of the century the Berlin city, ring and suburban railways had a need to replace the four-coupled locomotives with more powerful ones. The requirements here included to accelerate a 240-ton passenger train consisting of 14 cars between the stations to a speed of 60 km/h. At that time, those responsible still saw difficulties in meeting these requirements with electric traction. Thus, Wittfeld ordered powerful six-coupled tank locomotives. Since the axle load in Berlin permitted 17 tonnes instead of the 14 tonnes of the Vienna city railway, this was favorable to achieve the required performances.

In addition to the conventional superheated two-cylinder T 11 and T 12 locomotives, the T 6 was also developed, which operated with saturated steam but had three generously dimensioned cylinders. While the outside cylinders were installed between the leading axle and the first driving axle as usual and acted on the second driving axle, the inner cylinder was located horizontally in front of the leading axle and acted on the first driving axle. The leading axle was designed as an Adams axle, while the trailing axle, together with the third driving axle, formed a Krauss-Helmholtz bogie. A Langer-Marcotty design smoke-consuming device was used in the boiler, which burned the soot in the firebox by supplying air from the top.

The tests had shown that the cylinders were oversized compared to the boiler and led to a high coal consumption. They were also too large compared to the adhesive weight, resulting in an adhesion coefficient of less than three and meaning that the locos often slipped when starting. Furthermore, the required acceleration performance could not be achieved, while the more economical T 11 and T 12 achieved it. So the number of the T 6 remained with the twelve pre-production locomotives.

Two of the twelve locomotives went to the Altona division. The inside cylinder was removed from the Berlin locomotives by 1908. They were mainly used for express freight trains and as temporary help at times of heavy traffic, while their sisters, which clearly outnumbered them, pulled the suburban trains. In 1913 they were relocated to other divisions, so that after the First World War five served as OKl1 with the PKP. The locomotives remaining in Germany were retired shortly after the end of the war, so that they did not receive Reichsbahn numbers.