Named after Felix Dzhershinskiy, the former chief of the Soviet secret police, the FD20 was the most powerful series-built steam freight locomotive in the pre-war Soviet Union.
Based on modern U.S. American design, roughly 3,000 of these 130-ton engines were built at the Voroshilovgrad (also called: Lugansk) Locomotive Works in the 1930s.
With an axle load of 20-ton (hence the name), the FD required a solid railbed which was rarely present in the front-near regions.
So, the FD20, as well as her modernized FD21 version, operated mainly in the rear yielding front supply tasks to the ubiquitous Series O^B and Series E steam engines.