The BR 18.4 was born in the JA Maffei workshops in Munich. The first copy was delivered on July 16, 1908. The axles are of "Pacific" layout with large diameter wheels. Until then it was the largest machine built by this manufacturer and is still considered "The most beautiful locomotive of the German railways". The S 3/6 had excellent long-distance performance, in 1951 it hauled a 150-tonne train 820 km from Hamburg to Munich, stopping only to load water. The definition S is for "Schnellzuglocomotiven" long-distance train and 3/6 for the ratio of driving axles with respect to the total of its axles.

Mostly it served in Bavaria on long-distance trains, but it also hauled such famous trains as the Orient Express and Rheingold, the Ostend-Vienna Express or the Paris-Carlsbad-Prague Express. Multiple variations were applied throughout its history, mainly in the driver's cabin, boiler and motor mechanisms.