Prussian T 4

Under the designation T 4, the Prussian State Railways grouped various different tank locomotives with two coupled axles and a carrying axle, which were primarily developed for suburban traffic. The engines were produced by various manufacturers in the period between 1882 and 1899. The early batches were not yet normalized and can in turn be divided into four sub-variants. What they had in common was the front arrangement of the carrying axle, which meant the wheel arrangement 2-4-0, and the same cylinder dimensions with a diameter of 420 mm and a stroke of 610 mm. The cylinders were still in front of the leading axke, which had a negative impact on running behavior.

The oldest variant was the Moabit type, six of which were manufactured by Borsig from 1882 and had a fixed leading axle. The boiler pressure was ten bars, as was the case with the Altona design supplied by Union Gießerei Königsberg from 1888 onwards. One difference with these was that the leading axle was designed as an Adams axle and thus enabled better negotiation of curves. From this ten locomotives were completed. The so-called Berlin type, which was created from the Moabit type and was also produced from 1884, achieved the largest number of 68 pieces in total. While the first six units were delivered with an Adams axle and ten bars of boiler pressure, the rest did not have the moving axle and the pressure was increased to twelve bars.

With a boiler pressure of already twelve bars, but still a fixed leading axle, Borsig produced 14 units in 1884 and Henschel in 1888, which were designated as the Magdeburg type. They were used in the suburban services of Berlin and Magdeburg and could hold more water than their predecessors.

The first standardized variant known as the T 4 was the Hanover design, which was used not only in the city that gave it its name, but also in the suburban services of Gdansk and Kassel. To achieve smoother running, the cylinders were moved between the forward and the first coupled axle and now the rear coupled axle was powered. Between 1885 and 1890, 24 machines were built, most of which were built by Hanomag and some by Henschel and Hartmann.

The T 4¹, which was derived from the Berlin form but, in contrast to this, was built according to standards, was the strongest in terms of numbers. The only major change was the elimination of the steam dome and the use of a regulator cap instead. Between 1890 and 1899, Henschel manufactured 169 engines, some of which went to other customers. In addition to two examples for the Royal Prussian Military Railway, the Reichseisenbahnen Alsace-Lorraine ordered ten units and the Lübeck-Eutiner Eisenbahn ordered eight more. The T 4¹ was given the class 70⁷⁰ in the Reichsbahn renumbering plan, but was completely phased out with the exception of road number 70 7007 by 1925.

The T 4² had a special position between its sisters because it had a trailing axle (wheel arrangement 0-4-2T) and had been developed for use on branch lines. They had a Crampton boiler and were built 63 times between 1889 and 1897 by Henschel and Schichau.

The last type was the T 4³, which was intended for the Werra Railway between Eisenach and Lichtenfels in Bavaria and of which only three examples had been delivered by Schichau in 1898. They had the longest wheelbase of all variants of the T 4 and were the only ones to have a Krauss-Helmholtz bogie to improve curve negotiation. They also did not come to the final renumbering as the class 70⁷⁰, since they were retired in 1924.