Operation Weserübung was the codename for Nazi Germany's assault on Denmark and Norway during World War II and the opening operation of the Norwegian Campaign. The name comes from the German for Operation Weser-Exercise (Unternehmen Weserübung), the Weser being a German river.
In the early morning of 9 April 1940 – Wesertag ("Weser Day") – Germany invaded Denmark and Norway, ostensibly as a preventive maneuver against a planned , and openly discussed , Franco-British occupation of both these countries. After the invasions, envoys of the Germans informed the governments of Denmark and Norway that the Wehrmacht had come to protect the countries' neutrality against Franco-British aggression. Significant differences in geography, location and climate between the two countries made the actual military operations very dissimilar.
The invasion fleet's nominal landing time – Weserzeit ("Weser Hour") – was set to 05:15 AM German time, equivalent to 04:15 Norwegian time.
In October 1939, the chief of the German Kriegsmarine, Grand Admiral Erich Raeder, discussed with Adolf Hitler the danger posed by British bases in Norway and the possibility of Germany seizing these bases before the United Kingdom could. The navy argued that possession of Norway would allow control of the nearby seas and serve as a staging base for future submarine operations against the UK. But at this time, the other branches of the Wehrmacht were not interested, and Hitler had just issued a directive stating that the main effort would be a land offensive through the Low Countries.
Toward the end of November, Winston Churchill, as a new member of the British War Cabinet, proposed the mining of Norwegian waters in Operation Wilfred. This would force the ore transports to travel through the open waters of the North Sea, where the Royal Navy could interdict them. Churchill assumed that Wilfred would provoke a German response in Norway. When that occurred, the Allies would implement Plan R 4 and occupy Norway. Though later implemented, Operation Wilfred was initially rejected by Neville Chamberlain and Lord Halifax, due to fear of an adverse reaction among neutral nations such as the United States. After the start of the Winter War between the Soviet Union and Finland in November had changed the diplomatic situation, Churchill again proposed his mining scheme, but once more was denied.
In December, the UK and France began serious planning for sending aid to Finland. Their plan called for a force to land at Narvik in northern Norway, the main port for Swedish iron ore exports, and to take control of the Malmbanan railway line from Narvik to Luleå in Sweden on the shore of the Gulf of Bothnia. Conveniently, this plan also would allow the Allied forces to occupy the Swedish iron ore mining district. The plan received the support of both Chamberlain and Halifax. They were counting on the cooperation of Norway, which would alleviate some of the legal issues. But stern warnings issued to both Norway and Sweden resulted in strongly negative reactions in both countries. Planning for the expedition continued, but the justification for it was removed when Finland sued for peace in March 1940.
Between 14 January and 19, the Kriegsmarine developed an expanded version of this plan. They decided upon two key factors: that surprise was essential to reduce the threat of Norwegian resistance (and British intervention); the second to use faster German warships, rather than comparatively slow merchant ships, as troop transports. This would allow all targets to be occupied simultaneously, as transport ships only had limited range. This new plan called for a full army corps, including a mountain division, an airborne division, a motorized rifle brigade, and two infantry divisions. The target objectives of this force were the following:
The plan also called for the rapid capture of the kings of Denmark and Norway in the hopes that would trigger a rapid surrender.
On 21 February 1940, command of the operation was given to General von Falkenhorst. He had fought in Finland during World War I and therefore was familiar with arctic warfare. But he was only to have command of the ground forces, despite Hitler's desire to have a unified command.
The final plan was code-named Operation Weserübung ("Exercise on the Weser") on 27 January 1940. It would be under the command of the XXI Army Group and include the 3rd Mountain Division and five infantry divisions, none of the latter having yet been tested in battle. The initial echelon would consist of three divisions for the assault, with the remainder to follow in the next wave. Three companies of paratroopers would be used to seize airfields. The decision to send also the 2nd Mountain Division was made later.
Initially the plan was to invade Norway and to gain control of Danish airfields by diplomatic means. But Hitler issued a new directive on 1 March that called for the invasion of both Norway and Denmark. This came at the insistence of the Luftwaffe to capture fighter bases and sites for air-warning stations. The XXXI Corps was formed for the invasion of Denmark, consisting of two infantry divisions and the 11th motorized brigade. The entire operation would be supported by the X Air Corps, consisting of some 1,000 aircraft of various types.
On 12 March, the UK decided to send an expeditionary force to Norway just as the Winter War was winding down. The expeditionary force began boarding on 13 March, but it was recalled - and the operation cancelled - with the end of the Winter War. Instead the British cabinet voted to proceed with the mining operation in Norwegian waters, followed by troop landings.
The first German ships set sail for the invasion on 3 April. Two days later, the long-planned Operation Wilfred was put into action and the Royal Navy detachment led by HMS Renown left Scapa Flow in order to mine Norwegian waters. The mine fields were laid in Vestfjord in the early morning of 8 April. Operation Wilfred was over, but later that day, the destroyer Glowworm, detached on 7 April to search for a man lost overboard, was lost in action with the German cruiser Admiral Hipper and two destroyers belonging to the German invasion fleet.
On 9 April, the German invasion was underway and the execution of Plan R 4 was promptly started.
Strategically, Denmark's importance to Germany was as a staging area for operations in Norway, and of course as a border nation to Germany which would have to be controlled in some way. Given Denmark's position in the Baltic Sea the country was also important for the control of naval and shipping access to major German and Russian harbors.
Small and relatively flat, the country was ideal territory for German army operations, and Denmark's small army had little hope. Nevertheless, in the early morning hours, a few Danish troops engaged the German army, suffering losses of 16 dead and 20 wounded. Germany never gave any official number of losses, but these were probably heavier, with 12 armored cars and several motorcycles and cars destroyed. Four German tanks were damaged and one Heinkel 111 shot down. Two German soldiers were temporarily captured by the Danes during the brief fighting.
Just before the initial German invasion, the German ambassador to Denmark, Renthe-Fink, called the Danish Foreign Minister Munch and requested a meeting with him. When the two men met 20 minutes later Renthe-Fink declared that German troops were at that moment moving in to occupy Denmark to protect the country from Franco-British attack. The German ambassador demanded that Danish resistance cease immediately and contact be made between Danish authorities and the German armed forces. If the demands were not met, the Luftwaffe would bomb the capital, Copenhagen.
As the German demands were communicated, the first German advances had already been made, with forces landing by ferry in Gedser at 04:15 and moving north. German Fallschirmjäger units had made unopposed landings and taken the Storstrøm Bridge as well as the fortress of Masnedø.
At 04:20 local time, 1,000 German infantrymen landed in Copenhagen harbor from the minelayer Hansestadt Danzig, quickly capturing the Danish garrison at the Citadel without encountering resistance. From the harbor, the Germans moved towards Amalienborg Palace to capture the Danish royalty. By the time, the invasion forces arrived at the king's residence, the King's Royal Guard had been alerted and other reinforcements were in their way to the palace. The first German attack on Amalienborg was repulsed, giving Christian X and his ministers time to confer with the Danish Army chief General Prior. As the discussions were ongoing, several formations of Heinkel 111 and Dornier 17 bombers roared over the city dropping leaflets. Faced with the explicit threat of the Luftwaffe bombing the civilian population of Copenhagen, and only General Prior in favour of continuing to fight, the Danish government capitulated in exchange for retaining political independence in domestic matters.
At 05:45, two squadrons of German Me 110s attacked Værløse airfield on Zealand and wiped out the Danish Army Air Service by strafing. Despite Danish anti-aircraft fire, the German fighters destroyed 11 Danish aircraft and seriously damaged another 14.
The Danish capitulation resulted in the uniquely lenient Occupation of Denmark, particularly until the summer of 1943, and also in postponing the arrest and deportation of Danish Jews until nearly all of them were warned and on their way to refuge in Sweden. In the end, 477 Danish Jews were deported, and 70 of them lost their lives, out of a pre-war total of Jews and half-Jews at a little over 8,000.
Though Denmark had little immediate military significance, it had strategic and to some extent economic importance.
Norway was important to Germany for two primary reasons: as a base for naval units, including U-boats, to harass Allied shipping in the North Atlantic, and to secure shipments of iron-ore from Sweden through the port of Narvik. The long northern coastline was an excellent place to launch U-boat operations into the North Atlantic in order to attack British commerce. Germany was dependent on iron ore from Sweden and was worried, with justification, that the Allies would attempt to disrupt those shipments, 90 percent of which originated from Narvik.
The initial invasion force was transported in several groups by ships of the Kriegsmarine:
In the far north, Norwegian, French and Polish troops, supported by the Royal Navy and the RAF, fought against the Germans over the control of the Norwegian harbour Narvik, important for the year-round export of Swedish iron ore (The Swedish harbour of Luleå is blocked by ice in the winter months). The Germans were driven out of Narvik on 28 May, but due to the deteriorating situation on the European continent, the allied troops were withdrawn in Operation Alphabet – and the Germans recaptured Narvik on 9 June, by then deserted also by the civilians due to massive Luftwaffe bombing.
Operation Weserübung did not include a military assault on (likewise neutral) Sweden – there was no need. By holding Norway, the Danish straits and most of the shores of the Baltic Sea, the Third Reich encircled Sweden from the north, west and south – and in the East, there was the Soviet Union, the successor of Sweden's and Finland's arch-enemy Russia, on friendly terms with Hitler under the terms of the Molotov-Ribbentrop Pact. A small number of Finnish volunteers helped the Norwegian Army against Germans in an ambulance unit.
Sweden's and Finland's trade was totally controlled by the Kriegsmarine. As a consequence, Germany put pressure on neutral Sweden to permit transit of military goods and soldiers on leave. On 18 June 1940, an agreement was reached. Soldiers were to travel unarmed and not be part of unit movements. A total of 2.14 million German soldiers, and more than 100,000 German military railway carriages, crossed Sweden until this traffic was officially suspended on 20 August 1943.
On 19 August 1940, Finland agreed to grant access to its territory for the Wehrmacht, with the agreement signed on 22 September. Initially for transit of troops and military equipment to and from northernmost Norway, but soon also for minor bases along the transit road that eventually would grow in the preparation for Operation Barbarossa.