The first Russian chief advisor to the MPB was Major General Ivan Serov, a well-trained Stalinist experienced with Soviet security organs. Serov became commander of the NKVD-run militsiya during World War II. He worked as chief of the NKVD Secret Political Department, before becoming People's Commissar of Internal Affairs of the Ukrainian Soviet Socialist Republic in the USSR. In 1941–1945, he was the First Deputy People's Commissar of the State Security and later – Deputy People's Commissar of Internal Affairs of the Soviet Union. Once he became main advisor to the UB in March 1945, Ivan Serov oversaw the kidnapping of 16 top Polish politicians and underground resistance leaders, secretly transported them to Moscow, where they were tortured and thrown into jail after the staged Trial of the Sixteen. None survived.