OKo1s were often used with local trains. This engine (OKo1-11, ex KPEV Essen 8918, then DRG 78 379, Vulcan 3892/1922) was photographed by Geoff Plumb (http://geoff-plumb.fotopic.net – thanks for permission!) near Czempin on July 3, 1974. It was withdrawn in 1975.




The sole survivor in Poland, OKo1-3, on display at the Railway Museum, Warsaw. Photo taken on May 19, 2001.




Another photo of the OKo1-3, taken on September 5, 2006...




…yet another one, taken on the same occasion...




...and cab interior.




Side drawing of the DR class 781-5 from TB vol.2.




According to my data, this picture of the OKo1-18 was taken at the Jaworzno depot in May 1960. Photo from my collection.




TCDD 3705 (Henschel 20554/1925) at the Çamlik Buharli Lokomotif Muzesi, Turkey; photo taken on September 30, 2007.




 78 009, DR, Vulcan 2761/1912, somewhere in Eastern Germany, August 1971. Photo by Werner Nagel (from my collection).



Two pictures from www.de.wikipedia.org by someone who wishes to be known as MPW57: 78 1009-6 (Vulcan 2791/1912) with original service number 78 009, photographed in Potsdam on May 17, 1993…



…and 78 510 (Vulcan 1972/1924) on display at the Verkehrsmuseum Nürnberg, July 14, 1985.



Most probably this is Stettin 8410 (Vulcan 2762/1912). Later 78 010, it remained in service with DR until 1969. Location and date unknown. Photo from my collection.



An unidentified class T18 engine, location and date unknown. Source: Die Lokomotive December 1920.



DB 78 243 (formerly KPEV Essen 8470, Vulcan 3769/1922), photographed in Essen on March 12, 1960. This locomotive was withdrawn five years later. Photo by Herbert Schambach (postcard from my collection).



Beautifully preserved DB 78 468 (Henschel 20166/1923), Wattenscheid-Höntrop, September 17, 2016. Photo by someone who wishes to be known as Tenderlok (source: www.commons.wikimedia.org).

KPEV class T18 was the penultimate one in the long line of Prussian tank locomotives. It was intended as a replacement of older passenger tank engines (classes T10, T11 and T12), mainly with commuter and suburban trains, so ability to run at full speed (100 km/h) in both directions was mandatory. In order to assure good running qualities during reverse running, a rather exotic axle arrangement 2-3-2 was chosen, for the first time. Such arrangement, in Europe sometimes referred to as Baltic, was used in several locomotive types in Austria, France, Hungary, Spain and The Netherlands, but none of these was particularly widespread; with a notable exception of Hungarian class 303, all were tank engines. In North America it was known as Hudson and appeared by a simple extension of the Pacific with large firebox that had to be supported by a trailing truck rather than a single axle. Compared to other North American types, however, Hudsons were not numerous, totaling less than 500 examples in all.

In T18, axle arrangement resulted in a long locomotive (exactly 3 m longer than T10) of somehow peculiar appearance. Apart from this, new engine made use of modern, but already proven design concepts. Boiler was very similar to that of class P8 with the same moderate pressure of 12 bar. Grate was slightly shorter and overall heating surface was reduced by a few percent. Cylinder bore was reduced from 575 to 560 mm, but piston stroke remained unchanged, although drivers were reduced in diameter by 100 mm. First ten examples were built by Vulcan-Werke of Stettin (today Szczecin) and delivered in late 1912 (serial numbers 2753 through 2762). During service tests, T18 proved itself a good and tough machine, capable of hauling even light express trains: with a 350-tonnes draft, 90 km/h could be easily maintained. Initially running qualities were found not entirely satisfactory and maximum speed was set at 90 km/h. After some corrections of wheelsets balancing and resultant improvement it was increased to 100 km/h. KPEV were entirely satisfied with their new acquisition and in 1914 ordered it in quantity. Production engines differed from first ten examples in being fitted with feedwater heater.

Until the end of the war, about 140 examples were accepted by KPEV, all built by Vulcan. Production against KPEV orders continued until 1923; in all, 332 engines were given Prussian service numbers (last of them was ‘Essen 8960’, Vulcan 3916/1923). Apart from these, Vulcan in 1915 built 28 T18s for the state railways of then-German Alsace-Lorraine; after WWI they were taken over by SNCF as class 232TC. From the above-mentioned fleet of KPEV machines, nineteen (assigned to KED Saarbrücken) were in 1920 transferred to the Saarbahnen. Two were transferred to Belgian railways and numbered 9403 and 9408; both were withdrawn before 1925. The rest were incorporated into newly-formed Deutsche Reichsbahngesellschaft (DRG) as class 781-5; in 1925, they were allocated serial numbers 78 001 through 145, 78 166 through 282 and 78 351 through 401. Between 1923 and 1925, 122 more were built against DRG orders by Vulcan (69) and Henschel (53), later designated 78 402 through 523; five more were built by Vulcan at own risk in 1924 and purchased by DRG in 1927 to become 78 524 through 528. Moreover, 27 examples were built for Saarbahnen by Vulcan, Henschel, Hanomag and Société Franco-Belge de Matériel de Chemins de Fer of La Croyère, Belgium; when the Saar region was incorporated into the German Reich in 1935, all T18s owned by Saarbahnen were taken over by DRG as 78 283 through 328.

In 1919, Württembergische Staatsbahn ordered twenty T18s from Vulcan (serials 3513 through 3532, service numbers 1121 through 1140); after all German railways were merged into DRG, they became 78 146 through 165. Last machines of this type were, quite surprisingly, built in late 1930s, when private Eutin-Lübecker Eisenbahn (ELE) ordered a single example from Henschel (23241/1936). Due to its satisfactory performance, in particular high tractive effort combined with moderate axle load, second engine was ordered three years later (24563/1939); it differed from its predecessor in having two sand domes instead of one, Knorr-Tolkien feedwater pump and in some minor details. On January 1, 1941, these two engines were taken over by DRG as 78 329 and 78 330. This gives a grand total of 536 examples built for various German railways, of which 508 were included in the DRG rosters – as far as I know, no French 232TC was impressed into German service during WWII. Further eight, with slightly modified boilers, were ordered by Turkish CFOA (Société de Chemins de Fer Ottoman d’Anatolie) railways. They were built by Henschel in 1925 (serials 20550 through 20557), but delivered to newly-formed TCDD railways and given service numbers 3701 through 3708.

Four DRG engines of this type were written off before the end of the WWII; two of them, 78 184 and 78 191, were later taken over by PKP and restored in service. Of remaining 504 examples, the majority – 416 – went to DB. Several were withdrawn immediately afterwards, but 409 remained in use. Compared to other steam locomotives, their service was quite long: last of them, 78 246 (Vulcan 3772/1922) was written off in December 1974. DR were left with 53 machines; most were written off in early 1960s and the last, 78 427 (Vulcan 3922/1923) survived in service until August 1971. Four examples were taken over by the Soviets and re-numbered 77.xxx (where xxx stood for DRG number); they probably saw very little service, if any. Czechoslovakian railways ČSD acquired (according to www.beitraege.lokomotive.de) two machines, which were not restored in service (78 280 and 78 376) and had no class designation assigned; EZ confirms only the first of them, scrapped in 1952. Three more (78 131, 78 168 and 78 495), also with no ČSD numbers assigned, were transferred to PKP in August and September 1945.

No machine of this type served with PKP before WWII, but after 1945 twenty-nine were acquired and impressed as class OKo1. Most of them had been built by Vulcan, except OKo1-22, which was built by Franco-Belge for Saarbahnen (s/n 2385/1925, service number 8444, later DRG 78 326). All were assigned to the Poznań District Management and remained there throughout their service. They were used mainly with local and suburban trains and enjoyed a good opinion. Their performance was similar to that of Ok1 (ex-Prussian P8), tractive effort was almost the same and ability to run at full speed in both directions made them particularly suitable for secondary lines, where many terminal stations had no turntables. Later they were supplemented by indigenous TKt48s, but soldiered on until early 1970s. On January 1, 1971, twenty-two were still in service and last four, OKo1-15, -16, -19 and -23, survived until 1975. According to SK, four trucks from scrapped OKo1s are still used for works transport at the ZNTK (Railway Stock Repair Works) in Ostrów Wielkopolski. One engine has been preserved: OKo1-3 (Vulcan 3610/1920, KPEV Essen 8428, then 78 189), withdrawn in September 1972, it can be seen on static display at the Railway Museum in Warsaw. Further five T18s have been preserved in Germany and TCDD 3705 (Henschel 20554/1925) can be seen at the Çamlik Buharli Lokomotif Muzesi (Çamlik steam locomotive museum) in Turkey.

Main technical data







Years of manufacture


1912 – 1939


Total built / used in Poland


5361) / 292)


Tender class




Axle arrangement




Design maximum speed




Cylinder bore


2 x 560


Piston stroke




Engine rating


 676 / 920


Tractive effort


10 900


Boiler pressure




Grate dimensions

m x m

2.42 x 1.01


Firebox heating surface




Distance between tube plates




Number of flue tubes




Heating surface of flue tubes




Number of smoke tubes




Heating surface of smoke tubes




Evaporating surface, total




Superheater heating surface




Diameter of drivers




Diameter of idlers front/rear


1000 / 1000


Total weight, empty


83 850


Total weight, working order


106 000


Weight on drivers, working order


51 100


Weight with tender, empty




Weight with tender, working order




Maximum axle load




Axle base (with tender)


11 700


Overall length (with tender)


14 800


Brake type




-       Plus eight slightly different engines for Turkey.

-       Some sources erroneously give 31.

-       Some sources give 138.3 m2.

-       90 km/h in first ten examples.


List of vehicles can be found here.


References and acknowledgments


-       http://www-personals.umich.edu/~khmiska (website by Kurt H. Miska, unfortunately no longer active);

-       TB vol.2;

-       Lokomotiv-Archiv Württemberg  by H. Lohr and G. Thielmann, Transpress, Berlin, 1988;

-       SK, various issues;

-       www.beitraege.lokomotive.de (locomotive database by Ingo Hütter);

-       Monographic article by Ryszard Stankiewicz (SS vol. 144).