The need for a heavy tank, carrying high booking is well understood in the USSR. According to the national military theory, such tanks were needed for the hacking of the enemy and the breakout or overcoming fortified zones. Most armies of developed countries had their own theories and practices to overcome the powerful enemy fortified positions, experience was acquired during the first world war. Modern at that time, fortified lines, such as the Maginot line or the Mannerheim line was even theoretically impossible. There was a misconception that the tank was created during the Finnish campaign to break through the Finnish Permanent fortifications (the Mannerheim line). Actually the tank began to be designed at the end of 1938, when it became abundantly clear that the concept of mnogobašennogo heavy tank, a t-35, is deadlocked. It was obvious that the presence of a large number of towers is not an advantage. But the huge size of the tank just weight it and do not allow the use of sufficiently thick armor. The tank was the Chief initiator of creation of the AUTOMOTIVE RED COMCOR d. g. Pavlov. In the late 1930 's, efforts were made to develop the tank reduced (compared to the t-35) size, but with thicker armour. However, the designers did not dare to refuse the use of multiple towers: it was believed that a gun will be fighting with the infantry and suppress the firing points, and the second must be anti-tank — to combat armour. New tanks, developed in the framework of this concept (QMS and t-100), were dvuhbašennymi, armed 76-mm and 45 mm guns. And just as an experiment developed a smaller version of the QMS is a single Tower. Due to the reduced length of the machine (on two supporting roller) that had a positive effect on dynamic characteristics. Unlike its predecessor, KV (so called experimental tank) received a diesel engine. The first tank was manufactured at the Leningrad Kirov plant (LKZ) in August, 1939. Originally, the lead designer of the tank was a. s. Ermolaev, then n. l. spirits. November 30, 1939, the winter war started. The military did not miss the occasion to test the new heavy tanks. The day before the beginning of the war (November 29, 1939) QMS, t-100 KV and sent off to war. They gave 20-th tâželotankovoj Brigade, equipped with medium tanks t-28. The first battle of the SQUARE took 17 December Hottinenskogo defense zone ruptures of the Mannerheim line.