Steam locomotive without tender type T18 of Prussian origin created on the basis of engineer Robert Garbe concept, dedicated to passenger trains (also express trains) running pendulously on routes, which endpoints do not provide the possibility of turning the locomotives to have the chimney in the direction of travel. Production between 1912-1927 took place mainly in Vulcan company plants in Szczecin, since 1922 also in Henschel & Sohn in Cassel (Kassel). Since 1924 the locomotives were also manufactured by the Société Franco-Belge and La Croyère (3 machines). In 1925 the German Railways took over 459 units of this kind, designated as 780-5 series. Between 1945 - 1946 29 locomotives were included in the inventory of the Polish State Railways for which the designation of OKo1 series was intended. All locomotives capable of movement were assigned to District State Railways Managent in Poznań, (DOKP Poznań) where they were used by the following locomotive sheds: Osobowa Poznań, Leszno, Gniezno, Głogów, Zbąszynek, Zielona Gora and Jarocin. In 1945 the OKo1-3 locomotive (designation DRG 78 189) was included in the inventory of Szczecin District State Railways Managent. After some repairs the locomotive started its service at Leszno locomotive shed and ended it in Jarocin. On 29 September 1972 it was removed from the inventory.
Serial number and year of production:3610/1920
Maximum speed:100 km/h
Steam overpressure in the boiler:1,2 MPa (12 at)
Wheel diameter of wheel sets:1000/1650/1000 mm
Water/ Coal supply:12 m³/ 4,5 t
Service mass of steam locomotiv:105 000 kg
Length over buffers:14 800 mm