Prussian state railways

For the most part the locomotives listed in the Prussian classification system were not built under state direction, but independently procured by the individual railway companies. In many cases they were only brought into the Prussian railway inventory when the ownership of their respective railway organisations was later transferred to the state authorities.

This explains their unusually high numbers with about 80 classes and variants, the overwhelming majority of which were constructed between 1877 and 1895. In 1889, Prussian standards were laid down in order that the number of classes could be reduced in the future.

The division of locomotives into class variants and different designs showed a clear predominance of tank engines. These were procured in widely varying, sometimes, large quantities totally some 9000 in all. That reflects a structure that largely consisted of unconnected branch lines (Kleinbahnen) for which no long-range locomotives – i.e. tender locomotives – had to be built. In terms of pure numbers, goods locomotives dominated, representing some 12,000 out of a total fleet of around 30,000 in Prussian state ownership.

According to Hütter and Pieper the original classification system for Prussian locomotives was largely drawn from the Prussian Eastern Railway (Prussian Ostbahn). Under that, the locomotives only had running numbers without class designation. From the locomotive's running number however its purpose could be deduced based on the following allocation of numbers:

Because each railway division numbered its locomotives independently using this scheme, there was a locomotive number 120, for example, almost everywhere. As a result, the name of the division was used with the number in order to distinguish them. The full designation for a locomotive with the number '120' went something like "Hannover 120" or "Cöln linksrheinisch 120". However it soon became evident that the numbering structure was too limited, because over time more locomotives entered service than its sequence of numbers had allowed for. In addition, new types of engine were produced, for which no numbers had been allocated, for example four-couplers. This resulted in locomotives being allocated unused numbers outside of their designated sequence.

This all led to the introduction of a new system in 1906. For express train, passenger train, goods train and tank locomotives the group letters 'S', 'P', 'G' and 'T' were used together with a type number that specified the main classes.

So locomotives of average power were allotted to the '3' classes: S3, P3, G3 and T3. Less powerful engines were given lower numbers and more powerful engines higher numbers. In addition, superheated steam engines were to be given an even class number, whereas wet steam engines of a similar type were to be given the number below. Later further sub-divisions were introduced that had higher numbers. Furthermore, within the classes, running numbers were arranged in clear groups. Nevertheless, the complete designation still included the division name and the running number as well as the class letters and numbers.

Classes 1 to 3 mainly comprised the old private railway locomotives, left in the order of the individual divisions. In the lower-numbered classes there were the most varied types of engine sometimes with different wheelbases. So one could not really speak of a standard classification to begin with. It was expected that over time the older locomotives would be paid off so that only the newer standard locomotives would remain, classified in a logical and orderly fashion.

The Prussian state railways were, like all other German state railways, subordinated to the authority of the German Empire after 1920 and then went into the Deutsche Reichsbahn-Gesellschaft in 1924. Quite a few of the locomotives formerly ordered by Prussia continued to be supplied until 1926 and were still defined as Prussian locomotive classes in the Reichsbahn fleet until they were eventually renumbered.