[2] He began his military career by entering German service as a volunteer in the Royal Prussian 27th Jäger Battalion in March 1916 at the Lockstedter Lager in Germany, where he specialised as an artilleryman in a light howitzer battery.

From spring 1916 to January 1917, Hannuksela fought on the Eastern Front alongside the battalion at numerous battles near Riga, receiving experience in trench warfare, offensive operations and winter combat.

[3] In 1930 and 1933 Hannuksela was evaluated by his superior, kenraalimajuri Harald Öhquist, as a talented artilleryman and unit commander with room to grow, more suited to frontline leadership tasks than staff work.

The province had the responsibility of raising the 13th Division, which Hannuksela would command when the Soviet Union started the Winter War by invading Finland in November 1939.

[1] As commander of the 13th Division, subordinate to IV Corps, Hannuksela had the task of stopping the Soviet 8th Army advance along the coastal road in southern Ladoga Karelia, before it reached the regional capital of Sortavala.

[5] With the arrival of 45,000 troops and over 100 field artillery pieces as reinforcements in January, IV Corps was divided into battle groups ranging from battalion-sized formations up to the regimental level.

A major counteroffensive was planned, aimed at the complete destruction of the opposing Red Army formations by means of a single envelopment.

Both Hannuksela and VII Corps commander kenraalimajuri Woldemar Hägglund did not question their own planning or leadership capabilities but rather blamed the stalemate on the effective employment of artillery by the Soviets, lack of sufficient artillery support for the 19th Division and the low level of training and defensive mindset of the soldiers themselves, who were largely reservists, rear-echelon troops forced into combat roles or veterans of the Winter War.

A Soviet counterattack to retake the village from 13–15 July was defeated after which the breakthrough was expanded to the south through follow-up attacks on the 15th with the support of the newly attached Raskas Patteristo 14 (equipped with German 15 cm sFH 18).

[12] Outnumbered, the Soviets had to continuously withdraw to shorten their front-line and by 25 July VII Corps had advanced 40 kilometers from the border to the outskirts of Sortavala.

Hannuksela had a strong understanding of Kampfgruppe-style tactics but lacked the strength of will to deviate from the often incoherent orders emanating from corps headquarters.

When questioned by his subordinates on his decision-making, he saw such feedback as a personal attack, held fast to his thinking and frequently dismissed criticism from them with silence or arrogant responses.

[16][17] Such an inflexible leadership philosophy led to unnecessary losses on the battlefield, which in turn lowered troop morale and caused crises in command that hampered operations.