Soviet Railways series ИС (IS)

At the beginning of the thirties, the SŽD commissioned a locomotive for heavy passenger trains that had an axle load of 20 tonnes and a driver diameter of 1,850 mm. As wheel arrangement, 2-8-4 was chosen, which was used in the USA for fast freight trains, and the locomotive was named “ИС 20” (IS 20) after Josef Stalin, where the 20 stood for the axle load in tonnes. It was based on the 2-10-2 freight locomotive ФД (FD) and used the same boiler as well as other components from it.

It was the largest passenger steam locomotive in Europe at the time, but didn't show good running characteristics in curves at high speeds. From 1941 onwards, eleven locomotives were built with a larger superheater, which had an axle load of 21 tonnes and were therefore referred to as ИС 21. As part of the de-Stalinization, the ИС was renamed ФД^П in 1962, which distinguished it as a passenger variant of the ФД. The last ones were in use until 1972.