Like hundreds of other Finnish exile Red Guard fighters, Vähä joined the Red Army and fought with the Bolsheviks in the Russian Civil War. In the summer of 1919 Vähä served in Siberia, and was then sent back to Petrograd to join the military academy. In 1920–1923, Vähä took a three-year course at the international Petrograd Red Officer School, where he was joined by four of his brothers. During his time in the academy, Vähä took part in the arrests of the suspects of the Kuusinen Club Incident in September 1920, the suppression of the Kronstadt rebellion in March 1921, and the suppression of the East Karelian uprising in the winter of 1922. After the Battle of Kimasozero in January 1922, Vähä killed three captured Finnish White Guard soldiers on the orders of his platoon leader Toivo Antikainen. Antikainen was later captured in Finland, where he received a life sentence for the murders.