ET21 (also manufactured as Pafawag 3E) is a name for a Polish electric freight locomotive produced between years 1957 to 1971 in Pafawag. It was the first post-war Polish electric locomotive, designed in 1955. Besides being delivered for PKP, ET21 locomotives were delivered to the mining industry, where they are used up to now. History Mechanical part of the locomotive was designed in the Rolling-stock Industry Central Bureau of Construction (Pl.: Centralne Biuro Konstrukcyjne Przemysłu Taboru Kolejowego) in Poznań, basing on instructions from the Railway Electrification Office (Pl.: Biuro Elektryfikacji Kolei). Electrical part of ET21 locomotive was slightly based on Soviet VL22M locomotive. Production started in 1957 at Pafawag in Wrocław in co-operation with Dolmel (Wrocław), Elta (Łódź), Elester (Łódź) and Apena (Bielsko-Biała) companies. After first two units (prototypes) were ready the serial production started. At the beginning those locomotives bore E600 designation, which was changed to E06 and after introducing RN-58/MK0001 norm to present ET21. By the end of 1958 18 new machines were ready. After producing 70 first units and gaining significant experience Pafawag decided to introduce several technical changes into locomotives. This included decreasing weight by approx. 8 t., levelling weight on all axles, changing air intake system and crew cabin as well as installing electric carriage heating system. First locomotives were introduced into Warsaw-Katowice-Gliwice line. As the number of engines was increasing they started serving on all electrified lines in Poland. After the introduction of the EU06 and EU07 locomotives, the ET21 was systematically transferred to freight only service. Systematical withdrawal of this series began on the brink of the 1980s and 1990s and lasts until today. Some units are still used on mountainous areas, especially on Tarnów-Krynica-Zdrój, Kraków-Zakopane and Wrocław-Wałbrzych lines. The only running first-series ET21 locomotive is ET21-57 machine located in Chabówka railway museum. Service outside PKP Along with delivering locomotives for PKP Pafawag started selling machines for mining industry, specifically for Coal Mining Filling Materials Company (Pl.: Przedsiębiorstwo Materiałów Podsadzkowych Przemysłu Węglowego - PMP-PW). Those locomotives bore designation 3E - first series and 3E/1 - second, modernised series. The first locomotive delivered for PMP-PW was given 3E-10 number, the last one bore 3E/1-77 number. The main difference between PKP ET21 and 3E locomotives was that coal mining locomotives were lacking in carriage heating systems. 3E and 3E/1 machines were and are still used for transporting filling sand, power plant waste and coal, especially