DB locomotive classification
Originally, both Deutsche Bundesbahn and Deutsche Reichsbahn continued the classification system of the Deutsche Reichsbahn (DRG) – see also a short overview of the numbering system of the German railways. When UIC introduced a new classification system that could be processed by the computers of the late 1960s, DB did a major modification of their system, effective 1 January 1968.
Source: Wikipedia — DB locomotive classification (CC BY-SA 4.0)