During his studies, he became involved in the Jäger Movement,[1] which aimed at sending Finnish volunteers to receive military training in Germany.

[1] While in Germany, the Finnish volunteers formed the 27th Royal Prussian Jäger Battalion, fighting for the Imperial German Army on the Eastern Front of World War I.

The defense of Siilasvuo's forces prevented the Soviet 9th Army from reaching Oulu, which would have resulted in the bisection of Finland into two separate theatres of operation.

Historian Mikko Uola describes the book as "taking all credit for the success of Suomussalmi and completely ignoring other commanders who influenced the events, such as Siilasvuo's superiors Viljo Tuompo and Paavo Susitaival, as well as his subordinates such as Alpo Marttinen.

"[1] During the 1941 Finno-German negotiations regarding plans for a future war with the Soviet Union, the Germans proposed that the Finns would be in charge of operations in the South-Eastern Finland and east of Lake Ladoga, with overall command of both Finnish and German troops in the area falling under the Finnish commander-in-chief, Marshal Mannerheim.

[8] Despite the German reinforcements, III Corps was unable to reach Loukhi and by August both sides had settled for stationary warfare.

[9][10] By 6 October 1941, the situation at the front had improved to a point where Nikolaus von Falkenhorst and Siilasvuo discussed continuing the III Corps's advance towards Loukhi.

Due to Hitler's August order that the forces in the area were to go on the defensive, the plan was phrased as III Corp improving its positions.

[1] Following the end of the Siege of Leningrad in January 1944, the Finnish high command began preparations for a Soviet offensive.

As part of these preparations it split the Kannas Group, responsible for the defence of the Karelian Isthmus, into two corps-level formations on 4 March 1944.

However, following the failure of Operation Tanne Ost which involved a German attempt to capture Gogland from its Finnish defenders, the Finno-German cooperation completely broke down.

[20][21] During the subsequent Lapland War, Siilasvuo's III Corps was moved to northern Finland where it took overall command of all the Finnish forces participating in the operation.