During the Finnish Civil War, Hannuksela served as a section leader and artillery observer in the Jäger artillery brigade, participating in the battles of Tampere and Viipuri. He was promoted to "luutnantti" in April 1918 and was awarded the Cross of Liberty, 4th Class. After the civil war, Hannuksela received formal artillery education at the Finnish Artillery School from July 1918 to October 1918. After service as a battery commander until April 1919, his career path began to trend upwards. He was appointed as a coastal artillery battalion commander in April 1919, was promoted to "kapteeni" a month later and completed his artillery education in 1920. In 1923 he fulfilled a field grade officer training course and on Independence Day was promoted to "majuri". From 1924-1926 he studied at the Finnish War Academy, with perfect scores in tactics and weapons. Following his education, Hannuksela spent the late 1920s and early 1930s as an artillery regiment commander, with postings in the coastal-, heavy- and field artillery branches and was promoted to "everstiluutnantti" in 1927 and "eversti" in 1930.