OKa1 was the designation used by the PKP for light steam locomotive of the former Latvian State Railways Tk series. Built in 1928–1934, the units were of German and Latvian production. After 1945, it was used by the Polish State Railways; it was the only steam locomotive in Poland with one driving axle.

History

In 1928, management of the Latvian State Railways placed an order for the construction of light and economical locomotives to support suburban traffic. A total of 20 were purchased, of which the first three were built in

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

(Nos. 231–233) at the Hohenzollern plant in Düsseldorf. Locomotive trials were successful, so in 1931 a further six were ordered from German plants (234-236 - Krupp and 237-239 - Henschel), with final assembly and the construction of various parts (such as the driver's cab and water tanks) carried out by the Latvian Fēnikss plant in

Riga Riga ( ) is the capital, Primate city, primate, and List of cities and towns in Latvia, largest city of Latvia. Home to 591,882 inhabitants (as of 2025), the city accounts for a third of Latvia's total population. The population of Riga Planni ...

. Slight improvements to the design were made over the first batch of locomotives delivered. In 1933–1934, the last 11 locomotives were built in Latvian railway workshops: 6 at TFD in

Daugavpils Daugavpils (see also other names) is a state city in southeastern Latvia, located on the banks of the Daugava River, from which the city derives its name. The parts of the city to the north of the river belong to the historical Latvian region ...

(240-242, 248–250) and 5 at TFL in

Liepāja Liepāja () (formerly: Libau) is a Administrative divisions of Latvia, state city in western Latvia, located on the Baltic Sea. It is the largest city in the Courland region and the third-largest in the country after Riga and Daugavpils. It is an ...

(243-247). They were used as an alternative to diesel railcars on lesser-used passenger routes. The locomotives were normally used on 1,524 mm gauge tracks, but also had interchangeable axles for use on

standard gauge A standard-gauge railway is a railway with a track gauge of . The standard gauge is also called Stephenson gauge (after George Stephenson), international gauge, UIC gauge, uniform gauge, normal gauge in Europe, and SGR in East Africa. It is the ...

tracks of 1,435 mm.

Usage

The locomotives were assigned to the depots in

Šķirotava Šķirotava is a neighbourhood of Riga, the capital of Latvia. It is located in the Latgale Suburb of Riga Riga ( ) is the capital, Primate city, primate, and List of cities and towns in Latvia, largest city of Latvia. Home to 591,882 inh ...

Jelgava Jelgava () is a state city in central Latvia. It is located about southwest of Riga. It is the largest town in the Semigallia region of Latvia. Jelgava was the capital of the united Duchy of Courland and Semigallia (1578–1795) and was the ad ...

Dyneburg Daugavpils (see also other names) is a state city in southeastern Latvia, located on the banks of the Daugava River, from which the city derives its name. The parts of the city to the north of the river belong to the historical Latvian region ...

, Rezekne and Krustpils. In September 1940, after the annexation of Latvia by the USSR, the steam locomotives were taken over by the

Soviet Railways The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

. During the

Great Patriotic War The Eastern Front, also known as the Great Patriotic War (term), Great Patriotic War in the Soviet Union and its successor states, and the German–Soviet War in modern Germany and Ukraine, was a Theater (warfare), theatre of World War II ...

, some of the Tk series locomotives were captured by the Germans, 5 of which were later recaptured by the Soviet

Red Army The Workers' and Peasants' Red Army, often shortened to the Red Army, was the army and air force of the Russian Soviet Republic and, from 1922, the Soviet Union. The army was established in January 1918 by a decree of the Council of People ...

, and after the war there were 12 steam locomotives of this series in the USSR. They were withdrawn by

in the 1950s, and a few were transferred to various industries. After 1945, there were two Tk locomotives on the

Polish State Railways The Polish State Railways ( , abbr.: PKP S.A.) is a Polish state-owned holding company (legally a sole-shareholder company of the State Treasury) comprising the rail transport holdings of the country's formerly dominant namesake railway oper ...

: No. 235 (marked as OKa1-1) and No. 242 (marked as TKa-242). Oka1-1 was withdrawn from service in 1969, and previously ran service trains in the area of the Łazy marshalling yard. The TKa-242 steam locomotive worked until 1957 in the depot in Kutno. The OKa1-1 locomotive was selected for museum preservation and is now housed in the Railway Museum in Warsaw. After the war, three locomotives were used on West German railways (withdrawn at the end of 1951), and one on East German railways. The other two were lost, while OKa1-1 was left behind, would be housed in the

Warsaw Railway Museum The ''Stacja Muzeum'' is located at the former Warsaw Główna PKP railway terminus and is very close to the Warszawa Ochota railway station. The museum's exhibits are divided into permanent and temporary collections — the latter being di ...

Technical details

The locomotives had bogies with an 1A1 axle system for use with superheated steam. The leading axle and drive axle were rigidly fixed to the underframe, the supporting rear axle was on a Bissel semi-truck (the opposite of what was the most common arrangement). The Tk series locomotives were equipped with a pneumatic mechanism that allowed a load reduction on the rear running axle and thus increased the load on the driving axle by 50% when starting the locomotive. The tractive weight as well as the load on the driving axle was 15.4 tons, with a maximum axle load of 17.3 tons. The locomotive had a boiler with 55 tubes, a diameter of 39.5 / 44.5 mm (heating area 20.5 m²) and 26 tubes having a diameter of 100.5 / 108 mm (heating area 24.6 m²). The boiler was equipped with a superheater, having an area of 21.8 m². It also had a twin-cylinder, twin engine configuration with a cylinder bore of 320 mm and a piston stroke of 520 mm and was equipped with a

Walschaerts valve gear The Walschaerts valve gear is a type of valve gear used to regulate the flow of steam to the pistons in steam locomotives, invented by Belgium, Belgian railway mechanical engineering, engineer Egide Walschaerts in 1844. The gear is sometimes name ...

. The Tk series in Latvia also included two other locomotives (and tender): Tk-226 with a C-axel arrangement and Tk-227 with a B-axel arrangement. Latvian locomotives of the Tk series should not be confused with the Lithuanian series of Tk locomotives.

References

{{Reflist Polish State Railways steam locomotives 2-2-2T locomotives Railway locomotives introduced in 1928 Latvian Railways Tk series Krupp locomotives Henschel locomotives