Germany invaded both Norway and Denmark on 9 April 1940. Norway was very important to Germany for two reasons: firstly as a base for naval units to harass Allied shipping in the North Atlantic and Arctic Oceans, and secondly to secure shipments of iron ore coming in from Sweden through the port of Narvik. During Operation Weserübung, Denmark fell in less than a day, becoming the briefest invasion in recorded military history. The Norwegians put up a stiffer resistance to the invading German forces. Nonetheless, by May the southern half of Norway was under German control. Following the German invasion of France and the Low Countries, the Allies were forced to evacuate Narvik, leaving the country to the Germans who would occupy it until the end of the war. After the invasion, Vidkun Quisling led the collaborationist government of Norway, based around the fascist Nasjonal Samling ("National Gathering") party.