What is "donnerbuchse"

The German term Donnerbüchse (plural: Donnerbüchsen, formerly Donnerwagen) means "thunderbox" and is the nickname for the four-wheeled, open, passenger coaches, built from 1921 onwards, that served with the Deutsche Reichsbahn. In contrast to their predecessors, they were made entirely of iron or steel. The name comes from the loud rumbling of these coaches as a result of their lack of damping. Even the immediate forerunners of these wagons were given the name despite their wooden construction. In the early days, they were also called Ackermann'sche Donnerbüchse ("Ackermann's thunderboxes") after the departmental head responsible for them in the Ministry of Transport.