Parovoz SU-211-75, Stary Oskol

Su is a Soviet 1-3-1 passenger steam locomotive, produced from 1924 to 1951.

Designed by the Kolomna Plant Design Bureau, based on the best single-type courier steam locomotive of the Russian Empire - series Sv. In comparison with the prototype, in the result of design changes, it was a universal passenger steam locomotive of qualitatively new design and the first steam locomotive created in the USSR, equally suitable for operation in fast and heavy passenger trains. In serial production since 1925. The Su appeared on the lines at the time when the USSR, having quickly got over the heavy consequences of the imperialistic and civil wars, was getting stronger and was on the way to a wide way of technical reconstruction of the industry and agriculture. In technical terms, the Su was a significant step forward compared to the former steam locomotives, opening up a further number of achievements of Soviet steam locomotive building technology. Since the beginning of the 1930s, it was the most widespread standard passenger steam locomotive on the USSR road network. Compared to other passenger steam locomotives, Su favourably distinguished by the best steam availability at the most forced boiler operation and low fuel consumption, which aroused admiration among steam locomotive brigades. During the period of operation, in order to improve performance characteristics and production manufacturability, the basic design of the steam locomotive was gradually subjected to four design upgrades, and, accordingly, Su series steam locomotives were manufactured in five design versions: "1st issue"; "2nd issue"; "3rd issue"; "4th issue". In the system of the USSR NKPS, since 1932. - Su steam locomotives were transferred from the category of "powerful" to the category of "average power" steam locomotives. During the Great Patriotic War they drove sanitary trains. In postwar years, operation of Su locomotives was a privilege for honored machinists with pre-war service record. They were used for train operation on the main lines till the end of the 1960s and on secondary lines till about 1978. According to operational and economical performances Su corresponds to the best world examples of passenger steam locomotives.