The steam locomotive Su 252-94 (Су252-94), initially numbered 3698, was completed at the Andrei Zhdanov Krasnoye Sormovo Factory in June 1950. From 1950 to 1959, the locomotive operated at the Taiga and Barnaul depot of the Tomsk railway, then it was transported to the Kirov depot, and since 1962, when it became an oil-fired loco, it operated at the Daugavpils depot of the Baltic railway until being included in the reserve. The locomotive arrived in Estonia in November 1976 as a mobile boiler, working on many railway sites in Tallinn, including the Pääsküla depot. As a locomotive, its kilometrage until 1972 was 1,967,599 km. It became the first outdoor exhibit of the Railway Museum in Haapsalu and stays here since June 20, 1997. The tender, built at the Krasnoye Sormovo Factory in 1948, belonged originally to the locomotive Su251-00 and could carry 27 m3 of water and 20 tonnes of fuel.The class Su locomotive (Су – сормовский усиленный) was designed in 1925 at the Kolomna Locomotive Works as an improved version of class S (С, Sormovo, 1910). A total of 2,680 units were manufactured in Kolomna and Sormovo until 1951. The Su 252-94 belongs to the fourth, modernised batch built in Sormovo in 1947–1951 (a total of 411 units). The calculated operating weight of the 4th batch Su locomotives along with a tender was 150 tonnes. Its boiler could produce up to 12 tonnes of steam per hour with a maximum power of 1,565 hp and maximum speed of 120 km/h. The class Su locomotives were used in Estonia to haul local passenger trains as well as long-distance fast trains. But after the motorisation of railways, they were used as mobile boilers. Over time, a total of 47 class Su locomotives have hauled trains in Estonia (including 8 locomotives from the 4th batch). Locomotives of batches I and II ran in Estonia since 1944, followed by locos of batch IV and later by locos of the 3rd batch. In the 1960s, the Su locomotives of batches I and II were withdrawn and their boilers sold and replaced with newer engines. Additionally, ten locomotives of the same type, including the Su 252-94, were brought to Estonia in the 1970s and 1980s to apply them as mobile boilers. By 1991, only three Su locos remained in Estonia.