During the Civil War in Finland (1918), Airo served in the artillery on the White side, taking part in battles near Viipuri.

In 1921 he was accepted into École Supérieure de Guerre, the French officer training academy, from which he graduated as a captain in 1923, at the age of 27.

Airo rose swiftly in rank, mainly because newly independent Finland needed suitable officers for the fledgling army.

After the Continuation War, the now Communist-dominated Valpo (the Finnish State Police) arrested him for his alleged involvement in the so-called Weapons Cache Case.

In 1982 President Mauno Koivisto awarded Airo with the Grand Cross of the Finnish Order of the White Rose with swords, which was a very rare honour in Finland.