Franz Krull Sk class
The Franz Krull Sk-class is a class of steam locomotive built by the Franz Krull metal works of Tallinn, Estonia between 1931-1940. The "Sk" were narrow-gauged and used oil shale as fuel, since it is the primary energy source in Estonia. A total of 16 units were produced, of which none has survived. The last "Sk", "Sk-156", was scrapped in 1980 in Beloretsk, Russia, where it was actively used until scrapping. List of "Sk" locomotives. Built in 1931: Built in 1935: Built in 1940: