The Series X was produced by Mytischi carriage building plant with assistance from specialists in Kharkov. The Series X tramcar was approved for use in 1927 for all cities in the USSR. By the end of 1936, Series X tramcars were in use in 73 Soviet cities. Following the outbreak of WWII, tramcars assumed greater importance given the shortage of other transport paricularly the transportation of workers to the factories manufacturing tanks and armaments.