During the Civil war in Soviet Russia in 1918 Aarne commanded the front in Karelia between Saimen and Ladoga Lake.

His military operations as a part of Karelian army concluded to holding a position south of Vuoksen.

His youth, his background as a hunter and his speaking Finnish made him an alternative to Gustaf Mannerheim.

But despite his successful initial career he left the Army in 1918 because he couldn't come to terms with German orientation.

Aarne Sihvo had run as a candidate for parliamentary elections in 1919 as a member of the National Progressive Party and won the majority of votes in his district.