DRG locomotive classification

The DRG locomotive classification system was developed by the German Imperial Railway Company or Deutsche Reichsbahn-Gesellschaft (DRG), which was formed in 1924 following the merger of the German state railways (Länderbahnen) in 1920. A common classification and numbering scheme was needed in order to organise effectively the four hundred or so different steam locomotive classes taken over from the state railways, as well as new locomotives.

Source: Wikipedia — DRG locomotive classification (CC BY-SA 4.0)