T4-SU were the first trams imported from Czechoslovakia to Tallinn. In years 1973-1979 sixty cars were bought (No. 250-309). New trams were much different from their German predecessors – not only because of the completely new design but also driving system which was half-automatic now. T4 can be connected into three-car trams in case construction of trolley is appropriate for it. In our town all T4 are connected into two-car trams. Most of them are serving the fourth line. While in the beginning cars with successive numbers were connected then now such regularity has lost since some cars have been discounted.