Built in 1929 by German locomotive builder Henschel & Son, the Deutsche Reichsbahn Class 99.21 was a unique narrow gauge 0-6-0T steam tank locomotive built for the Wangerooge Island Railway on Wangerooge, one of the German-owned Friesian islands in the North Sea.

For hauling eight-wheeled passenger coaches a more powerful locomotive was needed.

After the procurement of diesel locomotives in 1958 she remained for a time as a reserve engine.

Today the locomotive is restored and is displayed as a monument on Wangerooge.

The wheels on the centre axle were made without flanges to improve curve running.