.After the First World War, with a smaller Austria, the BBÖ wanted to use tank locomotives for express trains in order to save the fees for turning locomotives on foreign turntables for services to border countries.

However, the Südbahn 629 series was too weak for these tasks and their fuel and water capacities were too small, so that they had to be supplemented at great expense abroad.

In 1936, six copies with Nicholson thermic syphons were reordered, the changed dimensions of which are shown in the table.

[1] A third order comprising ten locomotives had already been delivered to the Deutsche Reichsbahn, which classified the machines as the 78.6.

78.618 was acquired in 1976 by the Austrian Society for Railway History (Österreichische Gesellschaft für Eisenbahngeschichte, ÖGEG) as its first standard-gauge steam locomotive and, in the years up to 1986, was refurbished to be operational on a voluntary basis by association members.