Franco-British plans for intervention in the Winter War

During the early stages of World War II, the British and French Allies made a series of proposals to send troops against the Soviet Union, which had invaded Finland in 1939 as a consequence of the Molotov-Ribbentrop Pact. The plans involved the transit of British and French troops and equipment through neutral Norway and Sweden. The initial plans were abandoned due to Norway and Sweden declining transit through their land, fearing their countries would get pulled into the war. The Moscow Peace Treaty ended the war in March 1940 precluding the possibility of intervention.

Background
In February 1940, a major Soviet offensive broke through the Mannerheim Line on the Karelian Isthmus, exhausting Finnish defenses and forcing the country's government to accept peace negotiations on Soviet terms. At the news that Finland might be forced to cede its sovereignty to the USSR, public opinion in France and Britain, already favorable to Finland, swung in favor of military intervention. When rumors of an armistice reached governments in Paris and London, both decided to offer military support.



Initial Allied approaches
The first intervention plan, approved on 4–5 February 1940 by the Allied High Command, consisted of 100,000 British and 35,000 French troops that were to disembark at the Norwegian port of Narvik and support Finland via Sweden while securing supply routes along the way. Plans were made to launch the operation on 20 March under the condition of a formal request for assistance from the Finnish government (this was done to avoid German charges that the Franco-British forces constituted an invading army). On 2 March, transit rights were officially requested from the governments of Norway and Sweden. It was hoped that Allied intervention would eventually bring the two still neutral Nordic countries, Norway and Sweden, to the Allied side by strengthening their positions against Germany &mdash; although Hitler had by December declared to the Swedish government that Franco-British troops on Swedish soil would immediately provoke a German invasion.

However, only a small fraction of the Franco-British troops were intended for Finland. Proposals to enter Finland directly, via the ice-free harbour of Petsamo, had been previously dismissed. There was speculation in some diplomatic quarters, encouraged by German sources, that the true objective of the operation was to occupy the Norwegian shipping harbour of Narvik and the vast mountainous areas of the north-Swedish iron ore fields, from which it was assumed that the Third Reich received a large share of its iron ore (actually 30% in 1938), regarded as critical to war production. If the governments of France and Britain later broke their pledge not to seize territory or assets in Norway and Sweden, and Franco-British troops later moved to halt exports to Germany, the area could become a significant battleground between the Allies and the Germans.

The Franco-British plan, as initially designed, proposed a defense of all of Scandinavia north of a line Stockholm–Gothenburg or Stockholm–Oslo, i.e. the British concept of the Lake line following the lakes of Mälaren, Hjälmaren, and Vänern, which would provide a good natural defense some 1,700–1,900 kilometres (1,000-1,200 miles) south of Narvik. The expected frontier, the Lake line, not only involved Sweden's two largest cities, but could potentially result in large amounts of Swedish territory being either occupied by a foreign army or located in a potential war zone. Later, the plan was revised to include only the northern half of Sweden and the rather narrow adjacent Norwegian coast.

Norwegian and Swedish reaction
Despite this compromise, the Norwegian government denied transit rights to the proposed Franco-British expedition. The Swedish government, headed by Prime Minister Per Albin Hansson, also declined to allow transit of armed troops through Swedish territory, in spite of the fact that Sweden had not declared itself neutral in the Winter War. Instead, the Swedish government argued that, since it had declared a policy of neutrality in the war between France, Britain, and Germany, the granting of transit rights by Sweden to a Franco-British corps, even though it would not be used against Germany, was still an illegal departure from international laws on neutrality.

This strict interpretation appears to have been merely a pretext to avoid angering the Soviet and Nazi German governments, as it was abandoned after fifteen months. On 18 June 1941, the Swedish government quickly agreed to German demands for transit rights across Sweden for German troops on their way from occupied Norway to Finland, in order to join the German attack on the Soviet Union. A total of 2,140,000 German soldiers and more than 100,000 German military railway carriages would cross neutral Swedish territory for the next three years.

The Swedish Cabinet also decided to reject repeated Finnish pleas for regular Swedish troops to be deployed in Finland, and in the end the Swedes also made it clear that their present support in arms and munitions could not be maintained for much longer. Diplomatically, Finland was squeezed between Allied hopes for a prolonged war and Swedish and Norwegian fears that the Allies and Germans might soon be fighting each other on Swedish and Norwegian soil. Also, Norway and Sweden feared an influx of Finnish refugees if Finland lost to the Soviets.

Further Allied proposals and their effect on peace negotiations
While Germany and Sweden pressured Finland to accept peace on unfavorable conditions, Britain and France had the opposite objective. Different plans and figures were presented for the Finns. At first, both France and Britain promised to send 20,000 men who were to arrive by the end of February. By the end of that month, Finland's Commander-in-Chief, Field Marshal Mannerheim, was pessimistic about the military situation. Therefore, on 29 February the government decided to start peace negotiations. That same day, the Soviets commenced an attack against Viipuri.

When France and Britain realized that Finland was considering a peace treaty, they gave a new offer of 50,000 troops, if Finland asked for help before 12 March. Through Soviet agents in the French and British governments, indications of Franco-British plans reached Stalin, and may have contributed heavily to his decision to increase military pressure on the Finnish Army, while at the same time offering to negotiate an armistice.