The 50s in Polish railways were a time of serious development and improvements. In 1950, construction of TKt48 locomotives started and two years later a prototype of the Ol49 steam locomotive was built. 1953 brought several new types of electric rolling stock into PKP. Ten units of EP03 electric locomotives and 40 units of EW54 EMUs were ordered from Sweden. EW54 EMUs were sent to operate on lines connecting Warsaw with Mińsk Mazowiecki, Żyrardów and Sochaczew. Meanwhile, EP04 and EU20 locomotives were ordered from the DDR, along with EN56 and ED70 EMUs.