The Battle of Suomussalmi lasted from around December 8 1939 to January 7, 1940. On November 30, the Soviet 163rd division crossed the border between Finland and the Soviet Union and advanced from north-east towards the village of Suomussalmi which was only defended by one Finnish battalion (Er.P 15). Suomussalmi was taken with little resistance. The Soviet objective was to advance to the city of Oulu, effectively cutting Finland into half.

On December 9 the defenders were reinforced with a newly founded regiment (JR 27). Colonel Hjalmar Siilasvuo was given the command of the Finnish forces and he began immediate counter-measures to regain Suomussalmi. The main forces advanced on Suomussalmi but met resistance that caused the Finns serious losses.

On December 24 the Soviets counter-attacked, but failed to break through the surrounding Finnish forces.

Reinforced with two new regiments (JR 64 and JR 65) the Finns again attacked on December 27. This time they took the village and the Soviets retreated in panic over the surrounding frozen lakes.

During this time the Soviet 44th Division had advanced from the east towards Suomussalmi. It was entrenched on the road between Suomussalmi and Raate . Between January 4 and January 7 the division was divided into isolated groups (known as motti) and destroyed by the Finnish troops.

The Finns captured a great amount of war-booty, including tanks, field-guns and other weapons which were greatly needed by the Finnish army. The battle is often cited as an example how a small force, when properly lead and fighting in a familiar terrain, can defeat numerically vastly superior enemy. Factors which contributed to the Finnish victory include:

• Much greater mobility of Finnish troops afforded by skis and sledges.
• Flexible and often unorthodox strategy: Finns made Soviet field kitchens a prime target, greatly demoralising the enemy fighting in frigid sub-artic winter.
• Clothes and other equipment well suited for warfare in deep snow and freezing temperatures.