Swedish intervention in the Winter War

The Swedish Intervention in the Winter War was a short-lived but successful attempt by the Swedish Volunteer Corps, along with other Nordic volunteers, to prevent a Soviet invasion of Finland during the Winter War. The volunteers only engaged in a few skirmishes on ground and in the air, the only major battles they participated in being the battles of Salla and Honkaniemi. 
                    
                               Swedish aa-cannon cleaned

                    
                                   Swedish truck's

The term "volunteers" have often been used to describe the Nordic military support for Finland in the Winter War, although involvement by the government of Sweden has been debated over time. Nevertheless, the Swedish military sent enormous amounts of aid to Finland, including:
Approximately 2,000,000,000 crowns (US$ ~312,658,890) of financial aid - twice the size of the Finnish defense budget at the time

50,013,300 rounds of small arms ammunition
135,402 rifles
450 light machine guns
347 machine guns
301,846 artillery shells
144 field guns
92 anti-armor guns
100 anti-aircraft guns
300 sea mines
500 depth charges
83 motorcycles
83 cars
350 trucks
13 tractors
17 fighter aircraft
5 light bombers
1 transport aircraft
3 reconnaissance aircraft
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Swedish Intervention in the Winter War
Part of Winter War and World War II
Swedish soldiers inspecting a disabled enemy T-26 tank
Date 12 January – 13 March 1940 (2 months and 1 day) Location Eastern Finland Result End of the Winter War with the Moscow Peace Treaty Territorial changes Cession of the Gulf of Finland islands, Karelian Isthmus, Ladoga Karelia, Salla, and Rybachy Peninsula, and rental of Hanko to the Soviet Union
Belligerents
Sweden  Finland  Denmark  Norway Minor support from:  France  Hungary  Italy  United Kingdom	Soviet Union  Terijoki Government
Commanders and leaders
Ernst Linder  Carl Gustaf Mannerheim  Kurt Martti Wallenius  Voldemar Oinonen	Joseph Stalin  Kirill Meretskov  Kliment Voroshilov  Semyon Timoshenko
Strength
10,397 men:  8,402  1,010  895  13 tanks  26 aircraft Multiple Finnish armybattalions	20,000-30,000 men 58 tanks 29 aircraft in combat
Casualties and losses
523: 245 killed 250 wounded 28 captured 6 fighters lost Specific casualties	891: 640 killed 203 wounded 48 missing 9 tanks 4 fighters shot down 2 fighters damaged 6 bombers shot down 2 bombers damaged 7 more aircraft shot down 8 more aircraft damaged

The Winter War between Finland and the Soviet Union began in November 1939 after the Finnish government had rejected the Soviet claims to the Karelian Isthmus and all islands in the Gulf of Finland, as well as a demand to dismantle the defences in Finnish Karelia. Finland at the time was only officially allied with Estonia, as Sweden had rejected participation in the anti-Soviet alliance. 

The casus belli for the Soviet invasion was a claimed Finnish attack against the Russian village of Mainila, although it was later revealed that this was a false flag action conducted by the military of the Soviet Union.
                       
                       
                        
                        
                                                 Swedish

                        
                        
                                          Norvegian

                       
                        
                                
                        Danish  (danish pilot too, Morane and Gladiator pilots)

The battle of Salla was fought by Finnish-Swedish forces against the Soviet Union, beginning with a massive Soviet attack against the outnumbered Finnish defenders. Major General Kurt Martti Wallenius, the Finnish commander, ordered his men to retreat up the Kemijoki river where a defensive line could be easily maintained. After numerous suicide charges by the Soviet army, the sudden arrival of Swedish, Danish and Norwegian troops forced a Soviet withdrawal with heavy casualties of up to 500 men, compared to 187 among the Finns and 23 among the reinforcements.
                    
                                    Ex BT-5 tank

                    
                                Soviet BT-5 and T-26
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The battle of Honkaniemi was fought between Finnish and Soviet forces on 26 February 1940 and was the only tank battle of the Winter War. The Finns were supported by Swedish, Danish and Norwegian volunteers from the Nordic volunteer corps and had an unknown amount of infantry at their disposal (although it is known that they were much fewer than their Soviet enemies), as well as 13 Vickers 6-ton tanks. 
                    
Soviet tank men are looking destroyed Finn Vickers tanker's helmet

The Soviet corps of 58 tanks was able to beat back the attackers, losing 3 (Soviet sources) to 9 (Finnish sources) of their armored vehicles while Finland and its allies lost six. Added to that, 87 Finns and 140 Soviets were killed in the battle, while no casualties were reported among the volunteer corps. Although the Soviet casualties were larger than that of their adversaries, the Finnish colonel Voldemar Oinonen ordered a full retreat when he begun to doubt the chances of defeating the enemy.