The SMK, the two KV-1 prototypes and the two T-100 prototypes were put through proving trials before being tested operationally in combat at the Battle of Summa during the Winter War against Finland. The vehicles formed a company of the 91st Tank Battalion of the 20th Heavy Tank Brigade. The unit was under the command of the son of the Defence Commissar. After being immobilized by a mine, the SMK had to be abandoned and was not recovered for 2 months.