There was a Soviet tank testing unit. They had SMK, T-100, KV-1 prototype and t-34. T-34 was not used at allin the Winter War although I read that one or two would have been taking part in battle but litterature does not back this, obviously one or two SMK tanks were stopped by mines, KV U-O and U-1 were tested in attack with success. KV-1 Experimental KV, SMK and T-100 tanks were taken off the tests and thrown into battle. They formed a Heavy Tanks Company, included in the 91st Tank Battalion/20th Heavy Tank Brigade. Company Commander - Captain I. Kolotuskin. For the first time the company took part in combat on December 18 th 1939 supporting the attacks of the Soviet infantry in the Finnish Khotinnen Fortified Region. T-35 was not used although there were some 63 tanks available. During Babrbarossa the unreliability stopped using them and German reports claim they never had to fight any of them. They were abandoned by the crews due to michanical dysfunction or end of fuel. The crews had tried to destroy several of them. They were manned by ca 10 men. KV Tanks in the Winter War Only KV tank surived the testing for the future development after the Winter War testing.