Plan R 4

Since the outbreak of war in September 1939, that supply had been cut off and shipments from the other large supplier, Sweden, were essential for the production of military equipment.

In the Gulf of Bothnia, the northern part of the Baltic Sea, lies the Swedish port of Luleå from where ore is shipped during the summer.

Travelling inside Norwegian territorial waters for most of the trip, the shipping from Narvik was virtually immune to British interception.

The British and the French strategy was to use the Winter War, the invasion by the Soviet Union that has begun on 30 November 1939 as an excuse for seizing the Swedish ore fields in the north and the Norwegian harbours through which it was shipped to Germany.

Because of the danger of Allied or German occupation and of the war being waged on their territory, the Swedes and the Norwegians refused the transit requests.

The Altmark Incident of 16 February 1940 convinced Hitler that the Allies would not respect Norwegian neutrality and he ordered the plans for an invasion hastened.

[1] Troops were to be landed in Norway and were to move into Sweden to capture the Swedish mines but if serious military resistance from the Norwegians was encountered, the Allies were not to press the issue.

Adolf Hitler feared that the Allies would launch their invasion sooner or later and 9 April was set as the date of Operation Weserübung, the German attack on Denmark and Norway.