Winter War

On the morning of 30 November 1939, the Red Army crossed the Finnish border along its entire length while Soviet bombers struck Helsinki and other cities. Four Soviet armies advanced: the 7th on the Karelian Isthmus toward the Mannerheim Line, the 8th north of Lake Ladoga, the 9th into central Finland at Suomussalmi, Kuhmo and Salla, and the 14th from Murmansk against Petsamo on the Arctic coast. Two more armies were split off later: the 13th from the 7th Army's eastern wing on the isthmus at the end of December, and the 15th from the 8th Army north of Ladoga on 12 February. Stalin installed a puppet "Finnish Democratic Republic" under Otto Kuusinen at Terijoki, intending to instal it in Helsinki within weeks. Finnish forces, mobilised in October and commanded from 30 November by Marshal Carl Gustaf Emil Mannerheim, sent only covering troops to the border; on the isthmus these fell back to the Mannerheim Line within the first week.

By mid-December the Soviet advance on the isthmus stalled in front of the Mannerheim Line, a belt of bunkers and field fortifications from the Gulf of Finland through Summa and the Vuoksi waterway to Taipale on Lake Ladoga. Repeated Soviet assaults at Taipale, where the line met Ladoga, failed to dislodge the defenders for the duration of the war. Further north, in Ladoga Karelia, Finnish Group Talvela routed the Soviet 139th Division at Tolvajärvi on 12 December, and the 12th Division of Major General Woldemar Hägglund's IV Army Corps held the Kollaa river line from 7 December to the end of the war, at times with only four battalions against two Soviet divisions. In January Hägglund's counteroffensive cut the Soviet 168th and 18th Divisions off in mottis near Kitelä and Lemetti on the Ladoga shore.

The most dramatic Finnish successes came in the central wilderness. Around Suomussalmi, Colonel Hjalmar Siilasvuo's 9th Division encircled and destroyed the Soviet 163rd Division in December, then turned on the 44th Division sent to relieve it. Using "motti" tactics, small Finnish ski units cut the road-bound Soviet column into isolated pockets and annihilated them piecemeal along the Raate road into early January 1940. Estimates of Soviet losses in this sector run from about 22,500 to 27,000 men; the Soviet commander, Aleksei Vinogradov, was later court-martialled and shot. From 28 January Siilasvuo's division encircled the Soviet 54th Division east of Kuhmo, where it held out, supplied by air, until the end of the war. At Salla the Soviet 122nd Division was stopped short of Kemijärvi in December and pulled back to Märkäjärvi in January. In the far north the Soviet 14th Army took Petsamo in the first days of the war, reached the Salmijärvi nickel mines by mid-December and was held near Höyhenjärvi; it resumed its advance toward Nautsi in late February without reaching the interior.

Stalin's government dropped the Kuusinen puppet regime on 29 January 1940 and signalled willingness to negotiate directly with Helsinki, even as it prepared a heavier blow. On 7 January, Stalin replaced the invasion's original command with General Semyon Timoshenko, who reorganised the Soviet Northwestern Front, massed artillery, and retrained troops for set-piece assault against fortified lines. On 1 February the Soviets opened a bombardment that put some 300,000 shells into the Finnish line in its first 24 hours, followed on 11 February by a concentrated infantry and armour assault. Finnish defenders, exhausted after more than seventy days of continuous fighting and short of ammunition and reserves, could not close the gap at Summa; on 15 February Mannerheim authorised a general withdrawal of the II Corps from the Mannerheim Line to the intermediate line.

Through late February the Finnish army conducted a fighting retreat across the isthmus, contesting the intermediate line and on 27 February falling back to the rear line through Viipuri, Finland's second city, Tali and Kuparsaari to the Vuoksi. Soviet troops crossed the frozen Bay of Viipuri and on 5 March landed on its western shore at Vilaniemi, cutting the Helsinki road, while others broke into the city's eastern suburbs, pushed toward Tali and crossed the Vuoksi at Vuosalmi. The Finns still held Viipuri and Taipale when the ceasefire took effect at 11:00 on 13 March. On 23 February the Soviets set peace terms demanding the isthmus and the Ladoga shore; Finland, its army near the point of collapse but still an organised force, sent a delegation that reached Moscow on 7 March. The Moscow Peace Treaty was signed on 12 March and took effect the next day, ceding about 9–11 percent of Finnish territory, including the whole Karelian Isthmus with Viipuri, Ladoga Karelia, part of the Salla region and the Rybachi Peninsula, and leasing Hanko to the Soviet Union for thirty years. Some 430,000 Finns were evacuated from the ceded areas. Finland kept its independence; the Red Army's poor early performance shaped both Hitler's assessment of Soviet weakness and the Soviet military's own postwar reforms.