Under the designation T 9, the Prussian State Railways combined various types of tank locomotives with three coupled axles and one leading or trailing axle. They were mainly be used for tasks for which the T 3 was too weak. Originally 57 engines were built from 1891 for different lines with small differences. While the later T 9² and T 9³ had a leading axle, the original T 9 and T 9¹ had a trailing one.

After the T 9 was based on a design by Krauss in Munich, a large number of it's development T 9¹ were ordered from various manufacturers in Prussia. The weight and dimensions increased only slightly, but the diameter of the coupled wheels was increased to 1,350 mm. Thus, the maximum permitted speed could be at 60 km/h. The state railway variants of the T 9 were only certified for 45 or 50 km/h, only the Hessian locomotive was also permitted for 60 km/h.

A total of 426 engines were built up to 1901, of which 231 came to the Reichsbahn in 1925 and were mostly assigned to the 90^0-2 class. Ten pieces were incorrectly labeled as the 91 class, which was actually intended for the T 9² and T 9³. Like their predecessors, most of the T 9¹ were retired by around 1930 and some were sold to private railways. During the Second World War, some engines came back from Poland, the last of which survived until 1953.