The reason for purchasing the Prussian T 18 steam locomotive was that the T 12 used on Rügen and the T 10 stationed in the Mainz area no longer met the requirements. Performance, axle load and maximum speed of the new DRG Class 78 type of locomotive should correspond approximately to the P 8 (BR 38). 1911 conceptions were made with the proviso that these locomotives without turning on the turntable at the end stations fast and passenger trains in commuting on shorter and borderline routes to be able to carry. Since there were no forward and reverse locomotives at any time, the Prussian committee for locomotives decided to buy a tender locomotive with the symmetrical wheel alignment 2’C2 ‘. The Prussian T 18 was developed by the Szczecin Vilcan plants and also built the most copies.

For German railways 534 vehicles were built from 1912 to 1927, mainly by the Szczecin Maschinenbau AG Vulcan and from 1923 by Henschel, and from 1925 by Hanomag and Franco-Beige. 458 machines went to the Prussian State Railways and to the German Reichsbahn, 1919 received the Württemberg State Railways 20 copies and the Reichsbahnen in Alsace-Lorraine received 27 locomotives and were classified as T18 8401-8427.

The railways of the national territory procured 27 new copies of the class 78 from 1922 to 1925. Two copies, which became also the last T18, were built for the Eutin-Luebecker railway, which differed in some points from the model sheet XIV-4d and different arrangements of the dome and sandboxes.

After the end of the First World War 19 locomotives went to the railways of the national territory. Two remained in Belgium. The Recihbahn covered 460 Prussian T 18 from Prussia and 20 from the Württemberg State Railways with the operating numbers 78 001-282 and 78 351-528. The 78 093 came from Alsace-Lorraine and the 78 146-165 from Württemberg. Later, the DR joined the former Prussian machines of the Saar railways as 78 283-301 and their new buildings as 78 302-328. The steam locomotives DRG Class 78 of the Eutin-Lübecker railway were redesignated to 78 329 and 330.

After the end of the Second World War, 19 locomotives remained in Poland, which were classified by PKP under the name Oko1. The last retired in 1975 from the service.

The Deutsche Bundesbahn took over 424 locomotives and the Deutsche Reichsbahn 53. In 1965, the DR equipped a large number of their vehicles with the Giesl chimneys and Witte smoke deflectors. 1968 were only 35 steam locomotive Prussian T 18 in the inventory of the DR. In the German Federal Railways in 1968, the locomotives were re-designed for the 078 series. Aufch the DR drew the locomotives in 1970 to the 78 series.

The German Federal Railroad converted several class 78 steam locomotives for the Wendezugverkehr on shorter commuter trains (S-Bahn-Vorlaufbetrieb). The last Prussian T 18 were retired at the DB Mitt 70s in Bw Rottweil. A farewell trip took place with the BR 38 (P 8) on 31 December 1974.

» 78 009 belongs to the inventory of the Dresden Traffic Museum and is supervised by the IG Bahnbetriebswerk Dresden-Altstadt.
» 78 189 belongs as OKo 1-3 to the inventory of the Warsaw Railway Museum.
» 78 192 is a private property in the steam locomotive museum Tuttlingen
» 78 246 was parked as inaccessible in the German Steam Locomotive Museum. Since January 2018 she has been working for the EFZ e.V. in Rottweil.
» 78 468 (pictures) belongs to the Förderverein railway tradition and is also operated by this. Lengerich (Westphalia).
» 78 510 is part of the DB Museum.
» Turkish 37.05 is a museum locomotive at the Çamlık Railway Museum near Izmir.