Центральный телеграф
Over the years of the pre-World War II five-year plans (1929–1940), there was a rapid development of the Soviet communication system and industry. High-frequency equipment was introduced for long-distance communication. Use of such equipment allowed to transmit three, four, or 12 telephone calls over a pair of wires or 16 telegrams over a single telephone channel. In 1939, construction of a high-frequency three-channel line between Moscow and Khabarovsk (8,600 km) provided dependable communication between the USSR central regions and the Far East. By late 1940, the Moscow Central Telegraph Office had 22 facsimile lines. In 1941, a 12-channel line between Moscow and Leningrad was put into operation that meant the concurrent transmission of 12 telephone calls over a single pair of wires.