led to the introduction of the Class 25 condensing locomotive fleet in 1953. Soviet Union In the Soviet Union, locomotives were used to haul heavy freight trains. Two series were relatively common, the FD (for Felix Dzerzhinsky) with more than three thousand built through the 1930s, and the LV (Lebedyanskii, modified by the Voroshilovgrad factory). The FD class was developed from ALCO and Baldwin heavy freight locomotives that were imported to Soviet Russia, where they were designated as the Ta and Tb classes respectively. The first FD class locomotive was built at the Lugansk Locomotive Factory in 1931. In 1932, the Voroshilovgradskom plant began with the mass production of ФД20 locomotives. In the process of production, their construction was improved constantly. Production was interrupted at the outbreak of the Great Patriotic war in 1941 and was only resumed in 1942, when four locomotives were built in Ulan Ude. The total production was 2,927 locomotives of ФД20, and 286 locomotives of ФД21. The two subclasses only differed in respect of their types of superheater. In 1958, 1,054 FD class locomotives were sold to China, where they worked until the 1980s. A much lesser number were sold to North Korea at around the same time. The Russian locomotive class LV was developed from the previous L class 2-10-0 locomotive by the Voroshilovgrad factory. It used a feedwater heater to increase thermal efficiency and was the most efficient freight steam locomotive in the Soviet Union, with thermal efficiency of 9.3%. The first prototype was named OR18-01 (October Revolution factory, 18 tonne axle load). A total of 522 LV class locomotives were built. Several were preserved, including the first, OR18-01, and the last, LV-0522. Spain In Spain, the wheel arrangement was represented by one series of 22 locomotives. They were initially ordered for the Compañía del Norte, but RENFE kept the entire series in reserve. Built between 1941 and 1944 in the La Maquinista Terrestre y Maritima SA factory in Barcelona for hauling heavy coal trains, they were amongst the most powerful steam locomotives in Europe. They had three cylinders, but used simple expansion and were known as Santa Fe locomotives. Greece SEK (Sidirodromoi Ellinikou Kratous, Hellenic State Railways) class Μα (or class Ma; Mu-alpha) was a class of 2-10-2 steam locomotives built by Ansaldo and Breda in 1953. They were numbered Μα 1001-1020. The Μα locomotives were the last steam locomotives acquired by