In the 1930s, several narrow-gauge railways in the Harz Mountains ordered a series of steam locomotives with different wheel arrangements from Krupp, which had been developed according to standardized design principles. Although they looked similar to the standard locomotives of the Reichsbahn, there were some deviations from them. One of these locomotives was number 21II of the Nordhausen-Wernigerode railway, which was only built once because of the Second World War. It is one of the fastest narrow-gauge locomotives in Germany and is still in use today on the Harz narrow-gauge railways. It has been on the road with a new boiler since 2014. 