The Phony War ended on the night of April 8, 1940 when British warships mined the fjords of Norway to prevent Swedish iron ore from reaching Germany. The Norwegian Ambassador to London protested, but within hours the Allies learned of a massive German thrust through Denmark that was already landing in Norway. Denmark surrendered the same day to save herself, losing only a few soldiers.
What seemed like an incredibly swift response to Britain’s Norwegian minelaying was actually the culmination of months of planning. German paratroops secured airfields for air transports, and the German Navy sortied to cover destroyers with ski troops. A German landing in Oslo was driven off when the command heavy cruiser Blücher was sunk in the harbor, buying a short reprieve for the Norwegian government. But German merchant ships loaded with supplies and left in the fjords before the invasion sustained the rapidly moving land forces coming up from the south. The German paratroops were especially stunning to the Allies, who did not have anything like those formations at that time. Tough fighters, they would hold until relieved by the advancing ground forces.
British and French troops were hastily assembled and sent to Norway. Almost as soon as they landed they were forced to turn around or surrender, as the Germans swiftly moved through the country. Norwegian King Haakon VII left the country and set up a Government-in-exile in London, financed with Royal Norwegian gold. By the time of the invasion of France in May 1940, Norway had surrendered.
The French and the British, both reeling form the defeat at Norway, pledged not make a separate peace with Germany. This agreement would have serious implications two months later after the Germans invaded France.