The 'Battle of Suomussalmi' was fought between Soviet and Finnish forces for Suomussalmi, a town on the eastern side of central Finland, within the 'Talvisota' winter war (30 November 1939/8 January 1940).

The outcome was a Finnish victory against significantly superior forces of Kombrig Ivan F. Dashichev’s XLVII Corps within Komkor Mikhail P. Dukhanov’s (from 22 December Komkor Vasili I. Chuikov’s 9^th Army, and this battle is considered the most important Finnish victory in the northern half of Finland.

On 30 November 1939, Kombrig Andrei I. Zelentsov’s 13,562-man Soviet 163^rd Division crossed the border between Finland and the USSR and advanced from the north-east toward Suomussalmi. The Soviet objective was then to advance farther to the west in order to seize the city of Oulu, on the north-eastern coast of the Gulf of Bothnia, and thereby effectively cut Finland into northern and southern halves. This sector was held by only one Finnish detached battalion (Erillinen Pataljoona 15), which was placed near Raate, outside Suomussalmi.

The Soviets took Suomussalmi against little resistance on 7 December as only two incomplete companies of Finnish covering forces, part of the Ryhmä 'Susi' (from 25 December Eversti Paavo Siilasvuo’s 6,645-man Ryhmä 'Siilasvuo') within Kenraalimajuri Wiljo Tuopmo’s Pohjois-Suomen Ryhmä (North Finland Group), were available to undertake a small-scale holding action between the border and Suomussalmi, but the Finns destroyed the village before the arrival of the Soviet forces in order to deny the attackers any shelter, and withdrew to the opposite shores of the Niskanselkä and Haukiperä lakes.

The first larger-scale fighting began on 8 December, when the Soviets began to attack to the west across the frozen lakes, but failed completely. A second part of the Soviet forces led the attack to the north-west on Puolanka, which was defended by the recently arrived Erillinen Pataljoona 16, and this Soviet attack also failed. On 9 December, the defenders were reinforced by the arrival of a newly raised regiment, the 27^th Jalkaväkirykmentti. Eversti Hjalmar Siilasvuo assumed overall command of the Finnish forces in this sector, and began immediately planned and implemented a counterattack to retake Suomussalmi. The Finnish main force advanced on Suomussalmi, but failed to take the village and suffered serious losses. On 24 December, Soviet units counterattacked but failed to break through the surrounding Finnish forces.

Reinforced with two new regiments, the 64^th Jalkaväkirykmentti and the 65^th Jalkaväkirykmentti, the Finns once more attacked on 27 December and, on this occasion, took the village and compelled the Soviets to retreat. A large part of the Soviet strength managed to reach the border along the Kiantajärvi lake. During this time, Kombrig Aleksei I. Vinogradov’s 11,416-man Soviet 44^th Division, supported by the 1,600-man 3^rd NKVD Regiment, had started to advance from the east toward Suomussalmi, and was entrenched on the road between Suomussalmi and Raate, where it became caught up in the retreat of the other Soviet forces.

Between 4 January and 8 January, the 44^th Division was split into isolated groups which were attacked and destroyed in detail by the Finnish troops, now in the form of the 13,190-man 9^th Divisioona, which had compressed each Soviet group into a motti of isolated units which could neither be supplied not extracted, yielding much in the way of weapons and heavy equipment for the Finns.

The battle was a major victory for the Finns. Had the Soviet forces taken Oulu, the Finns would have faced the prospect of defending against the Soviet incursion into their country on two fronts and an important railway link to Sweden would have been severed. The successful outcome of the battle also gave a decisive boost to Finnish morale, both military and civilian.

In addition, in the 'Battle of the Raaste Road' Finnish forces on the road linking Raate and Suomussalmi captured a large quantity of military supplies, including 41 tanks, 70 pieces of artillery, 278 trucks, 1,170 horses, 20 anti-tank guns, 300 machine guns, 6,000 rifles and other weapons, all of which were swiftly pressed into Finnish service.

The 'Battle of Suomussalmi' is often cited as an example of how a small force, well led, suitably equipped and fighting in familiar terrain, can defeat an opponent of significantly greater numbers. Factors which contributed to the Finnish victory included firstly, that Finnish troops possessed higher mobility as they were equipped with skis and sleds whereas, by contrast, the Soviets were forced to use the roads by the weight and number of their heavy weapons and equipment confined; secondly, that the Soviet plan to cut Finland in half across the Oulu region appeared reasonable on a map but was inherently unrealistic as the region was mostly forested marsh with its road network consisting mainly of logging trails on which mechanised and motorised divisions became easy targets for the mobile Finnish ski troops; thirdly, the Finnish strategy was flexible and often unorthodox as, for example, the Finns targeting of Soviet field kitchens, which demoralised Soviet soldiers fighting in a sub-arctic winter. fourthly, that the Soviet army was poorly equipped, especially with regard to winter camouflage clothing whereas, by contrast, the Finnish troops' equipment was well-suited for warfare in deep snow and freezing temperatures; fifthly, that the Finns possessed very high morale, resulting from the fact that they were defending their homeland, whereas the Soviets possessed exclusively political reasons for their attack and swiftly lost their will to fight despite the continual efforts of Soviet propagandists' sixthly, that Soviet counter-intelligence failed and thus the Finns often intercepted Soviet communications, which relied heavily on standard phone lines; and seventhly, that the Finnish tactics involved exploitation of the local weather conditions in combination with the greatest possible tactical simplicity, as the final assault was a straightforward head-on charge, decreasing the chances of tactical errors.