The Norwegian campaign (8 April 10 June 1940) involved the attempt by Allied forces to defend northern Norway coupled with the resistance of the Norwegian military to the country's invasion by Nazi Germany in World War II. Planned as Operation Wilfred and Plan R 4, while the German attack was feared but had not yet happened, set out from Scapa Flow for the Vestfjorden with twelve destroyers on 4 April. The Royal Navy and the Kriegsmarine met at the First Battle of Narvik on 9 and 10 April, and British forces conducted the Åndalsnes landings on 13 April. The main strategic reason for Germany to invade Norway was to seize the port of Narvik and guarantee the delivery iron ore needed for German steel production. The campaign was fought until 10 June 1940 and saw the escape of King Haakon VII and Crown Prince Olav to the United Kingdom. A British, French and Polish expeditionary force of 38,000 troops landed in the north. It had moderate success but made a rapid strategic retreat after the Battle of France began on 14 May. The Norwegian government then went into exile in London. The campaign ended with the occupation of the entirety of Norway by Germany but elements of the Norwegian military escaped and fought on overseas. Background Outbreak of the Second World War Britain and France had signed military assistance treaties with Poland and two days after the German Invasion of Poland on 1 September 1939, both declared war on Nazi Germany. However, neither country mounted significant offensive operations and for several months there were no major engagements, and this period became known as the Phoney War or "Twilight War". Winston Churchill in particular wished to move the war into a more active phase, in contrast to Prime Minister Neville Chamberlain. During this time both sides wished to open secondary fronts. For the Allies, in particular the French, this was based on a desire to avoid repeating the trench warfare of the First World War, which had occurred on the Franco-German border. Following the outbreak of the Second World War, the Norwegian government had mobilized parts of the Norwegian Army and all but two of the Royal Norwegian Navy's warships. The Norwegian Army Air Service and the Royal Norwegian Navy Air Service were also called up to protect Norwegian neutrality from violations by the warring countries. The first such violations were