Shortly after graduation, in late 1914 Kohn was called into the infantry of the Austro-Hungarian Army. Following training he was sent to the Eastern Front in the Carpathian Mountains, facing the Imperial Russian Army. He was captured in 1915 and taken by the Russians to a prison camp in Central Asia (in present-day Turkmenistan). During the civil war following the Bolshevik revolution, the pro-western Czechoslovak Legions came into Central Asia and he was set free. With them he traveled further east (called by Czechs the "Siberian Anabasis"), until stopping at Irkutsk. The political situation then allowed him to return to Europe, arriving in 1920.