Oi1

Oi1-29 (Schwartzkopff 3450/1905), the sole surviving P6. Railway Museum, Warsaw, May 25, 2005.

Class 37^0-1 side drawing; source: TB vol.1 (© Lokomotiv-Revue)

First locomotive with steam superheater, Prussian Hannover 74, was completed by Vulcan in 1898 and advantages of such layout soon became obvious. Robert Garbe, perhaps the best known German locomotive designer, was a keen advocate of single-expansion engines running on superheated steam, which compared to compounds offered economy and simplicity. He managed to persuade railway officials to order for Prussian state railways KPEV (Königlich Preußische Eisenbahnverwaltung) a universal locomotive with the 1-3-0 axle arrangement for light express and mixed traffic, capable also of hauling freight trains on secondary lines. Intended versatility resulted in untypical diameter of drivers: it was set at 1550 mm, while Prussian passenger and freight engines of that time typically had 1750 mm and 1250 mm drivers, respectively.

Prototype (Cöln 21, Hohenzollern 1541/1901) with chamber-type superheater began tests in May 1902 and results were considered satisfactory, although at higher speed running qualities left something to be desired. Second engine, built by Schwartzkopff in 1903, and subsequent examples had drivers diameter increased to 1600 mm and cylinder bore from 520 to 540 mm. Some had Pielock steam dryer instead of superheater, while others had Lentz poppet valves instead of more typical Heusinger valve gear; both these novelties were later discarded due to poor reliability. In 1906 new tube-type Schmidt superheater was introduced and all earlier examples were later brought up to this standard. With new designation system introduced by KPEV in 1906, new machine was classed P6. Production continued until 1909 and totaled 272 machines for KPEV (some sources give 271, probably excluding the prototype). They were built by Hanomag (90), Henschel (37), Hohenzollern (5), Humboldt (25), MBG Karlsruhe (4) and Schwartzkopff (111). Further three (two in 1913 and one in 1916) were built by Linke-Hofmann for military railways (Königlich Preußische Militär-Eisenbahn). All these engines usually ran with 2’2’T16 four-axle tenders.

P6 was a modern and powerful machine, but weight distribution was not perfect. First coupled axle took higher load that the second, driven axle (15.2 and 14.9 tonnes, respectively) and running was somehow uneasy at higher speed. However, P6 had a tractive effort of 9 150 kG, while older P4¹ and P4² with two coupled axles yielded only 5 800 and 5 700 kG, respectively, with marginally lower axle load. The choice was obvious, but substantial improvement of the running qualities was achieved only with next passenger locomotive for KPEV – the famous P8, also designed by Garbe.

After WWI, Prussian railways kept 160 engines plus three from military railways (all later absorbed by DRG and classed 37^0-1); almost all went to East Prussia. Although P6 was, by Prussian standards, not a very numerous class, it found quite widespread use in post-war Europe, in France (16), Belgium (16), Italy (9), Lithuania (LG class K6, 6) and Latvia (LDV class Bn, 4, service numbers 51 through 54). Three went to Alsatia, to be taken over later by French railways, and four to Saarbahn, to be absorbed by DRG in 1935 as 37 164 through 167. According to the monographic article in SK, mentioned in the references, the ultimate fate of two machines remains unknown. Poland had the second largest fleet of P6s – in all, 44 engines were taken over after the war and classed Oi1 in 1923. Initially all were assigned to the regional management in Wilno; in late 1930s fifteen were transferred to Radom in central Poland. No wonder, thus, that in September 1939 most Oi1s fell into Soviet hands. Soviet ministry of transport (NKPS) retained their Polish designations, written on cabs in Russian script. Lithuanian and Latvian engines were also impressed into the NKPS service after these countries were occupied in June 1940. Many ex-P6s were rebuilt for the 1524 mm track, but the conversion program was not completed before 1941. In September 1939 German captured only six engines, impressed into the DRG service as 37 168 through 173. More, however, came later. After Fall Barbarossa Germans captured 31 ex-Polish Oi1s; they were designated 37 174 through 200 and 37 251 through 254 (numbers 37 201 through 206 were assigned to class G6 engines, operated by Lübeck-Büchener Eisenbahn, formally taken over by DRG in 1938, while 37 255 through 257 were ex-Lithuanian and Latvian engines, taken over by NKPS in 1940 and captured by Germans in 1941). Only fifteen ex-PKP engines were returned immediately after WWII, but they were joined by one ex-Lithuanian (LG K6 103), one ex-French and eighteen ex-DRG machines, as well as pre-war Oi101-12 (from Austro-Hungarian Heeresbahn), erroneously designated Oi1-4. Of these, five examples (including pre-war Oi1-25, and Oi1-44) were written off in 1946, so post-war class numbering ran up to Oi1-31 (Oi1-4 was later re-designated Oi101-2). Two ex-PKP engines returned by DR in 1956 (Oi1-21 and Oi1-33) were scrapped with no new service numbers assigned. Oi1s were used mainly with local passenger trains in northern Poland; most were assigned to the Gdańsk regional management. Until 1957, seventeen were withdrawn, but the rest survived until late 1960s and the last one (Oi1-6, Schwartzkopff 3635/1906, KPEV Bromberg 2103, then Oi1-11 and DRG 37 190) was withdrawn in March 1972. Ex-PKP Oi1s that remained in the Soviet Union, together with those acquired as war booty, survived in service until early 1950s; later many went to industry.

Oi1-29 (Schwartzkopff 3450/1905, KPEV Elberfeld 2110, then Oi1-7 and DRG 37 171), withdrawn in July 1968, has been preserved at the Railway Museum in Warsaw. This is the sole surviving locomotive of this type.

Main technical data

No.	Parameter	Unit	Value
1.	Years of manufacture	-	1901 – 1916
2.	Total built / used in Poland	-	275^1) / 44
3.	Tender class	-	16D1
4.	Axle arrangement	-	1-3-0
5.	Design maximum speed	km/h	75
6.	Cylinder bore	mm	2 X 540
7.	Piston stroke	mm	630
8.	Engine rating	kW/hp	750 / 1020
9.	Tractive effort	kG	9 150
10.	Boiler pressure	MPa	1.22
11.	Grate dimensions	m X m	2.28 X 1.0
12.	Firebox heating surface	m^2	11.49
13.	Distance between tube plates	mm	4 500
14.	Number of flue tubes	-	150
15.	Heating surface of flue tubes	m^2	83.6
16.	Number of smoke tubes	-	21
17.	Heating surface of smoke tubes	m^2	36.49
18.	Evaporating surface, total	m^2	134.93^2)
19.	Superheater heating surface	m^2	41.91
20.	Diameter of drivers	mm	1600
21.	Diameter of idlers front/rear	mm	1000 / -
22.	Total weight, empty	kg	51 660
23.	Total weight, working order	kg	57 100
24.	Weight on drivers, working order	kg	44 600
25.	Weight with tender, empty	kg	73 660
26.	Weight with tender, working order	kg	100 100
27.	Maximum axle load	T	15.2
28.	Axle base (with tender)	mm	14 050
29.	Overall length (with tender)	mm	17 958
30.	Brake type	-	Knorr, Westinghouse

1) Including 272 for KPEV and three for military railways; some sources give 271 for KPEV (probably excluding the prototype).

2) Other sources give 131.58 m².

References and acknowledgments

Comprehensive account of this class history and design can be found in the monographic article by Roman Witkowski in SK vol.3/1999. Information on individual examples has been taken from the impressive Ingo Hütter’s locomotive database (available at www.lokomotive.de).