The ET21 was the first electric locomotive to be completely developed and produced in Poland. After the EP02 had still used electric components delivered from English Electric, the electrics of the new locomotive were built in Poland, but in some respects were based on the Soviet ВЛ22М (VL22M). Pafawag designated the type 3E and it became ET21 in the PKP. They were designed to haul freight trains under 3 kV DC and had two three-axle bogies.
They had an hourly output of 2.400 kW and a continuous output of 1,860 kW. With a gear ratio for a top speed of 100 km/h, the starting tractive effort was 258 kN. Like most DC locomotives, power was controlled by setting all traction motors in series, by setting both bogies in parallel and the traction motors in serial or by setting all traction motors in parallel. Resistors were used for the transitions between these settings. Additionally, more power notches were created with three weak field settings.
After 70 locomotives of the original type 3E had been been built between 1957 and 1960, all others were built as type 3E/1 that was 7.7 tonnes lighter. Of a total production of 726, 658 went to the PKP. The others went to industrial and private railways which designated them ET21M. The PKP already withdrew the first locomotives of the original type 3E in the seventies, but a medium two-digit number of the 3E/1 survived into the 21st century. Some of the locomotives operated by private operators are still in use for backfilling mines in Upper Silesia.
