Tallinn has an all Tatra fleet running on an unusual 3'6" gauge. Between 1980 and 1990 73 Tatra KT4SU trams were delivered to Tallinn and between 1996 and 2009, 46 second hand KT4Ds were acquired from the former DDR. Since 2001 about 12 cars have been lengthened with a low floor centre section and reclassified KT6.
The lowest number I saw was 54 of 1980 in fleet livery.
123 was the last KT4SU delivered to Tallin in 1990. It is now a KT6 with a low floor centre section.