Answer
Kliment Voroshilov was replaced by Semyon Timoshenko as the People's Commissar of Defense during the Winter War. Voroshilov had overseen the disastrous initial Soviet campaign against Finland, and his replacement by Timoshenko signaled a shift in Soviet strategy. Timoshenko, a more experienced and capable military leader, was able to reorganize the Soviet forces and eventually secure a victory against the Finns.