Operation Weserübung

Operation Weserübung (German: Unternehmen Weserübung [ˈveːsɐˌʔyːbʊŋ]) was the code name for Germany's assault on Denmark and Norway during the Second World War and the opening operation of the Norwegian Campaign. The name comes from the German for "Operation Weser-Exercise", the Weser being a German river.

Operation Weserübung
Part of World War II

Clockwise from top left:
Date9 April – 10 June 1940
(2 months and 1 day)
Location
Result German victory
Territorial
changes		 Occupation of Denmark and Norway
Belligerents
Nazi Germany
Commanders and leaders
Strength
  • 9 divisions
  • 1 artillery battalion
  • 1 motorized rifle brigade
  • Total: 120,000
  • Norway:
  • 6 divisions: ~60,000
  • Denmark:
  • 2 divisions: ~14,500
  • Allies: ~35,000
  • Total: ~109,500
Casualties and losses
  • Kriegsmarine:
  • 1 heavy cruiser
  • 2 light cruisers
  • 10 destroyers
  • various U-boats, transports and smaller warships
  • Total:
  • 5,296 Casualties[1][2]
Royal Navy:
  • 1 aircraft carrier
  • 2 cruisers
  • 7 destroyers
  • 1 submarine
  • various transports and smaller warships
  • French Navy:
  • 1 destroyer
  • 1 submarine
  • Polish Navy:
  • 1 destroyer
  • 1 submarine
  • Norway:
  • 116 ships lost[3][4]
  • 1,700 killed
  • Denmark:
  • 26 killed
  • 23 wounded[5]
  • Allies: 4,902 Casualties
  • Total: 6,602 Casualties

In the early morning of 9 April 1940 (Wesertag, "Weser Day"), Germany occupied Denmark and invaded Norway, ostensibly as a preventive manoeuvre against a planned, and openly discussed, Franco-British occupation of Norway known as Plan R 4 (actually developed as a response to any German aggression against Norway). After the occupation of Denmark (the Danish military was ordered to stand down as Denmark did not declare war with Germany), 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 nations made the actual military operations very dissimilar.

The invasion fleet's nominal landing time, Weserzeit ("Weser Time"), was set to 05:15.

Political and military background
Main articles: Swedish iron ore during World War II, Plan R 4, Operation Wilfred, and Franco–British plans for intervention in the Winter War

Starting in the spring of 1939, the British Admiralty began to view Scandinavia as a potential theatre of war in a future conflict with Germany. The British government was reluctant to engage in another land conflict on the continent that it believed would be a repetition of the First World War. Therefore, it began considering a blockade strategy in an attempt to weaken Germany indirectly. German industry was heavily dependent on the import of iron ore from the northern Swedish mining district, and much of this ore was shipped through the northern Norwegian port of Narvik during the winter months.[6] Control of the Norwegian coast would serve to tighten a blockade against Germany.

In October 1939, the chief of the German Kriegsmarine, Grand Admiral Erich Raeder, discussed with Adolf Hitler the danger posed by potential 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 platform for staging submarine operations against the United Kingdom.[6] However, the other branches of the Wehrmacht were not then 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 intercept them.

Churchill assumed that Wilfred would provoke a German response in Norway, and the Allies would then implement Plan R 4 and occupy Norway. Though later implemented, Operation Wilfred was initially rejected by Neville Chamberlain and Lord Halifax for fear of an adverse reaction among neutral nations like the United States. After the start of the Winter War between the Soviet Union and Finland in November had changed the strategic situation, Churchill again proposed his mining scheme but once again was denied.

In December, the United Kingdom and France began serious planning for sending aid to Finland. Their plan called for a force to land in 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, that would also 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 co-operation of Norway, which would alleviate some of the legal issues, but stern warnings issued to both Norway and Sweden by Germany 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 with the Soviet Union in March 1940.

Planning

Following a meeting with Vidkun Quisling from Norway on 14 December,[7] Hitler turned his attention to Scandinavia. Convinced of the threat posed by the Allies to the iron ore supply, Hitler ordered Oberkommando der Wehrmacht (Armed Forces High Command; OKW) to begin preliminary planning for an invasion of Norway. The preliminary plan was named Studie Nord and called for only one army division.

Between 14 and 19 January, 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. That would allow all targets to be occupied simultaneously, which was impossible if transport ships were used, which travelled only slowly. The 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 the force were the Norwegian capital Oslo and nearby population centres, Bergen, Narvik, Tromsø, Trondheim, Kristiansand, and Stavanger. The plan also called for the swift capture of the kings of Denmark and Norway in the hope that this would trigger a rapid surrender.

On 21 February 1940, command of the operation was given to General Nikolaus von Falkenhorst. He had fought in Finland during the First World War and was familiar with Arctic warfare, but he was to have command only 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. The ground forces would be the XXI Army Corps, including the 3rd Mountain Division and five infantry divisions, none of the latter having yet been tested in battle. The first phase 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 also send the 2nd Mountain Division was made later.

Almost all U-boat operations in the Atlantic were to be stopped for the submarines to aid in the operation. Every available submarine, including some training boats, were used as part of Operation Hartmut in support of Weserübung.

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.

Preliminaries
German dead being brought ashore from the German naval tanker Altmark.
The heavy cruiser Admiral Hipper landing troops in Norway in 1940.

In February, the Royal Navy destroyer HMS Cossack boarded the German transport ship Altmark while in Norwegian waters, thereby violating Norwegian neutrality, rescuing British prisoners of war also held in violation of Norwegian neutrality (the Altmark was obliged to release them as soon as she entered neutral territory). Hitler regarded this response to German violation of Norwegian neutrality as a clear sign that the Allies were also willing to violate Norwegian neutrality, and so became even more strongly committed to the invasion.[6]

On 12 March, the United Kingdom 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 the battlecruiser HMS Renown, left Scapa Flow to mine Norwegian waters. The mine fields were laid in the Vestfjorden in the early morning of 8 April. Operation Wilfred was over, but later that day, the destroyer HMS Glowworm, detached on 7 April to search for a man lost overboard, was lost in action to the German heavy cruiser Admiral Hipper and two destroyers belonging to the German invasion fleet.

On 9 April, the German invasion was under way, and the execution of Plan R 4 was promptly started.

Invasion of Denmark
Main article: German invasion of Denmark (1940)
German Pz.Kpfw. I tanks in Aabenraa, Denmark, 9 April 1940

Strategically, Denmark's importance to Germany was as a staging area for operations in Norway, and also as a border nation to Germany which would have to be controlled in some way. Given Denmark's position on the Baltic Sea, the country was also crucial for the control of naval and shipping access to major German and Soviet harbours.

At 04:00 on 9 April 1940, the German ambassador to Denmark, Cecil von Renthe-Fink, called the Danish Foreign Minister Peter Munch and requested a meeting with him. When the two men met 20 minutes later, Renthe-Fink declared that German troops were then moving in to occupy Denmark to protect the country from Franco-British attack. The German ambassador demanded that Danish resistance cease immediately and that contact be made between Danish authorities and the German armed forces. If the demands were not met, the Luftwaffe would bomb the capital, Copenhagen.

German Leichter Panzerspähwagen armoured car in Jutland.

As the German demands were communicated, the first German advances had already been made, with forces landing by ferry in Gedser at 03:55 and moving north. German Fallschirmjäger units had made unopposed landings and taken two airfields at Aalborg, the Storstrøm Bridge as well as the fortress of Masnedø, the latter being the first recorded attack in the world made by paratroopers.[8]

At 04:20 local time, a reinforced battalion of German infantrymen from the 308th Regiment landed in Copenhagen harbour from the minelayer Hansestadt Danzig, quickly capturing the Danish garrison at the Citadel without encountering resistance. From the harbour, the Germans moved toward Amalienborg Palace to capture the Danish royal family. By the time the invasion forces arrived at the king's residence, the King's Royal Guard had been alerted and other reinforcements were on 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 He 111 and Dornier Do 17 bombers roared over the city dropping leaflets headed, in Danish/Norwegian, OPROP! (proclamation).

At 05:25, two squadrons of German Messerschmitt Bf 110s attacked Værløse airfield on Zealand and neutralised the Danish Army Air Service by strafing.[9] Despite Danish anti-aircraft fire, the German fighters destroyed ten Danish aircraft and seriously damaged another fourteen, thereby wiping out half of the entire Army Air Service.[9]

Danish troops at Bredevad on the morning of the German attack. Two of these soldiers were killed in action later that day.

Faced with the explicit threat of the Luftwaffe bombing the civilian population of Copenhagen, and with only General Prior in favour of fighting on, King Christian and the entire Danish government capitulated at approximately 06:00, in exchange for retaining political independence in domestic matters.

The invasion of Denmark lasted less than six hours and was the shortest military campaign conducted by the Germans during the war. The rapid Danish capitulation resulted in the uniquely-lenient occupation of Denmark, particularly until the summer of 1943, and in postponing the arrest and deportation of Danish Jews until nearly all of them were warned and on their way to refuge in Sweden.[10] 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.[11]

Invasion of Norway

Order of battle

The operation's military headquarters was Hotel Esplanade in Hamburg, where orders were given to, among others, the air units involved in the invasion.[12]

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.[6] The long northern coastline was an excellent place to launch U-boat operations into the North Atlantic 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% of which originating from Narvik.

The invasion of Norway was given to the XXI Army Corps under General Nikolaus von Falkenhorst and consisted of the following main units:

The initial invasion force was transported in several groups by ships of the Kriegsmarine:

  1. Battleships Scharnhorst and Gneisenau as distant cover, plus 10 destroyers with 2,000 mountaineering troops under General Eduard Dietl to Narvik
  2. Heavy cruiser Admiral Hipper and four destroyers with 1,700 troops to Trondheim
  3. Light cruisers Köln and Königsberg, artillery training ship Bremse, Schnellboot mothership Karl Peters, two torpedo boats and five motor torpedo boats with 1,900 troops to Bergen
  4. Light cruiser Karlsruhe, three torpedo boats, seven motor torpedo boats and Schnellboot mothership (Schnellbootbegleitschiff) Tsingtau with 1,100 troops to Kristiansand and Arendal
  5. Heavy cruiser Blücher, heavy cruiser Lützow, light cruiser Emden, three torpedo boats and eight minesweepers with 2,000 troops to Oslo
  6. Four minesweepers with 150 troops to Egersund

Concise timeline
The German landing sites during the initial phase of Operation Weserübung
Map of Oslofjord with Oscarsborg
  • Shortly after noon on 8 April, the clandestine German troop transport Rio de Janeiro was sunk off Lillesand by the Polish submarine Orzeł, part of the Royal Navy's 2nd Submarine Flotilla. However, the news of the sinking reached the appropriate levels of officialdom in Oslo too late to do much more than trigger a limited, last-minute alert.
  • Late in the evening of 8 April 1940, Kampfgruppe 5 was spotted by the Norwegian guard vessel Pol III. Pol III was fired at; her captain Leif Welding-Olsen became the first Norwegian killed in action during the invasion.
  • German ships sailed up the Oslofjord leading to the Norwegian capital, reaching the Drøbak Narrows (Drøbaksundet). In the early morning of 9 April, the gunners at Oscarsborg Fortress fired on the leading ship, Blücher, which had been illuminated by spotlights at about 04:15. Two of the guns used were the 48-year-old German Krupp guns (nicknamed Moses and Aron) of 280 mm (11 in) calibre. Within two hours, the badly damaged ship, unable to manoeuvre in the narrow fjord from multiple artillery and torpedo hits, sank with very heavy loss of life totalling 600–1,000 men.
  • The now obvious threat from the fortress (and the mistaken belief that mines had contributed to the sinking) delayed the rest of the naval invasion group long enough for the Royal Family, the Cabinet and members of Parliament to be evacuated, along with the national treasury. On their flight northward by special train, the court encountered the Battle of Midtskogen and bombs at Elverum and Nybergsund. As the Norwegian king and his legitimate government were not captured, Norway never surrendered in a legal sense to the Germans, leaving the Quisling government illegitimate. The Norwegian government-in-exile based in London remained, therefore, an Allied nation in the war.
  • At 7.06pm 7 Norwegian fighters are sent into battle to combat a wave of 70-80 enemy planes.
  • German airborne troops landed at Oslo airport Fornebu, Kristiansand airport Kjevik, and Sola Air Station – the latter constituting the first opposed paratrooper attack in history;[6] coincidentally, among the Luftwaffe pilots landing at Kjevik was Reinhard Heydrich.
  • Vidkun Quisling's radio-effected coup d'etat at 7.30pm on 9 April[13] – another first.
  • At 8.30pm the destroyer 'Æger' is attacked and sunk outside Stavanger by ten Junkers Ju 88 bombers, after it sank the German cargoship 'MS Roda'. Roda was a carrying a concealed ammunition and weapons cargo.
  • Cities/towns Bergen, Stavanger, Egersund, Kristiansand, Arendal, Horten, Trondheim and Narvik attacked and occupied within 24 hours.
  • Heroic, but wholly ineffective, stand by the Norwegian armoured coastal defence ships Norge and Eidsvold at Narvik. Both ships torpedoed and sunk with great loss of life.
  • First Battle of Narvik (Royal Navy vs Kriegsmarine) on 9 April.[14]
  • The German force took Narvik and landed the 2,000 mountain infantry, but a British naval counter-attack by the modernised battleship HMS Warspite and a flotilla of destroyers over several days succeeded in sinking all ten German destroyers once they ran out of fuel and ammunition.
  • Devastating bombing of towns Nybergsund, Elverum, Åndalsnes, Molde, Kristiansund N, Steinkjer, Namsos, Bodø, Narvik – some of them tactically bombed, some terror-bombed.
  • Main German land campaign northward from Oslo with superior equipment; Norwegian soldiers with turn-of-the-century weapons, along with some British and French troops (see Namsos Campaign), stop invaders for a time before yielding – first land combat action between British Army and Wehrmacht in World War II.
  • Second Naval Battle of Narvik (Royal Navy vs Kriegsmarine) on 13 April.[15]
  • Land battles at Narvik: Norwegian and Allied (French and Polish) forces under General Carl Gustav Fleischer achieve the first major tactical victory against the Wehrmacht in WWII, and the following withdrawal of the Allied forces (mentioned below); Fighting at Gratangen.
  • With the evacuation of the King and the Cabinet Nygaardsvold from Molde to Tromsø on 29 April, and the allied evacuation of Åndalsnes on 1 May, resistance in Southern Norway comes to an end.
  • The "last stand": Hegra Fortress (Ingstadkleiven Fort) resisted German attacks until 5 May – of Allied propaganda importance, like Narvik.
  • King Haakon, Crown Prince Olav, and the Cabinet Nygaardsvold left from Tromsø 7 June (aboard the British cruiser HMS Devonshire, bound for Britain) to represent Norway in exile (King returned to Oslo on the exact same date five years later); Crown Princess Märtha and children, denied asylum in her native Sweden, later left from Petsamo, Finland, to live in exile in the United States.
  • The founding of Sølvguttene ("The Silver Boys") by Torstein Eliot Berg Grythe (24 November 1918 – 1 May 2009), a Norwegian choir leader. The choir which for three years was used to promote antisemitism, and the aryan race, was later reformed after Grythe was released from the Grini detention camp in 1943.
  • The Norwegian Army in mainland Norway capitulated (though the Royal Norwegian Navy and other armed forces continued fighting the Germans abroad and at home until the German capitulation on 8 May 1945) on 10 June 1940, two months after Wesertag, that made Norway the occupied country that had withstood a German invasion for the longest time before succumbing.

In the far north, Norwegian, French and Polish troops, supported by the Royal Navy and the Royal Air Force (RAF), fought against the Germans over the control of the Norwegian harbour Narvik, important for the year-round export of Swedish iron ore. The Germans were driven out of Narvik on 28 May, but the deteriorating situation on the European continent made the Allied troops withdraw in Operation Alphabet, and on 9 June, the Germans recaptured Narvik, which was also now abandoned by civilians because of massive Luftwaffe bombing.

Encircling of Sweden and Finland
Iron ore is extracted in Kiruna and Malmberget and brought by rail to the harbours of Luleå and Narvik. (Borders 1920–1940)

Operation Weserübung did not include a military assault on (neutral) Sweden because 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, the west and the south. In the east, there was the Soviet Union, the successor of Sweden's and Finland's archenemy, 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.

Swedish and Finnish trade was dependent on the Kriegsmarine, and 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, as well as more than 100,000 German military railway carriages, crossed Sweden until that traffic was 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 it included transit for minor bases along the transit road that eventually would grow in preparation for Operation Barbarossa.

Nuremberg Trials

The 1941 Anglo-Soviet invasion of Iran, and the 1940 German invasion of Norway have been argued to be preemptive, with the German defense in the Nuremberg trials in 1946 arguing that Germany was "compelled to attack Norway by the need to forestall an Allied invasion and that her action was therefore preemptive".[16] The German defence was to attempt to refer to Plan R 4 and its predecessors. However, it was determined that Germany had discussed invasion plans as early as 3 October 1939 in a memo from Admiral Raeder to Alfred Rosenberg whose subject was "gaining bases in Norway".[17] Raeder had begun by asking questions such as "Can bases be gained by military force against Norway's will, if it is impossible to carry this out without fighting?"[17] Norway was vital to Germany as a transport route for iron ore from Sweden, a supply that the United Kingdom was determined to stop. One British plan was to go through Norway and occupy cities in Sweden.[a][b] An Allied invasion was ordered on 12 March, and the Germans intercepted radio traffic setting 14 March as deadline for the preparation. Peace in Finland interrupted the Allied plans.[c]

Two diary entries by Jodl dated 13 and 14 March did not indicate any high-level awareness of the Allied plan but also that Hitler was actively considering putting Weserübung into operation. The first said "Fuehrer does not give order yet for 'Weser Exercise'. He is still looking for an excuse".[17] The second "Fuehrer has not yet decided what reason to give for Weser Exercise".[17] It was not till 2 April 1940 that German preparations were completed and the Naval Operational Order for Weserübung was issued on 4 April 1940. The new Allied plans were Wilfred and Plan R 4. The plan was to provoke a German reaction by laying mines in Norwegian waters, and once Germany showed signs of taking action, UK troops would occupy Narvik, Trondheim, and Bergen and launch a raid on Stavanger to destroy Sola airfield. However, "the mines were not laid until the morning of 8 April, by which time the German ships were advancing up the Norwegian coast".[18] The International Military Tribunal at Nuremberg determined that no Allied invasion was imminent and so rejected the German argument that Germany was entitled to attack Norway.[17]

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See also

Notes
    • a "The British plan which was adopted was more modest. While ostensibly intended to bring Allied troops to the Finnish front, it laid its main emphasis on operations in northern Norway and Sweden. The main striking force was to land at Narvik and advance along the railroad to its eastern terminus at Lulea, occupying Kiruna and Gallivare along the way. By late April two Allied brigades were to be established along that line."[19]
    • b "The British held back two divisions from France, intending to put them into the field in Norway, and planned to expand their force eventually to 100,000 men. The French intended to commit about 50,000. The British and French staffs agreed that the latter half of March would be the best time for going into Norway."[20]
    • c "The objectives were to take Narvik, the railroad, and the Swedish ore fields","an intercepted radio message setting 14 March as the deadline for preparation of transport groups indicated that the Allied operation was getting under way. But another message, intercepted on the 15th, ordering the submarines to disperse revealed that the peace [in Finland] had disrupted the Allied plan."[21]

    References
    1. Lunde 2009, p. 542
    2. Derry 1952, p. 230
    3. Nøkleby, Berit (1995). "marinen". In Dahl; Hjeltnes; Nøkleby; Ringdal; Sørensen (eds.). Norsk krigsleksikon 1940–45 (in Norwegian). Oslo: Cappelen. pp. 262–264. ISBN 82-02-14138-9.
    4. Thowsen, Atle (1995). "marinens fartøyer". In Dahl; Hjeltnes; Nøkleby; Ringdal; Sørensen (eds.). Norsk krigsleksikon 1940–45 (in Norwegian). Oslo: Cappelen. p. 264. ISBN 82-02-14138-9.
    5. Zabecki 2014, p. 323.
    6. Booth 1998, pp. 44–49.
    7. Petrow 1974, p. 15.
    8. Outze 1962, p. 359.
    9. Schrøder 1999.
    10. Danish Jewish Museum 2003.
    11. Webb 2007.
    12. Jacobsen, Alf R. (2016). Kongens nei - 10. april 1940 (2nd ed.). Oslo: Vega Forlag. p. 42. ISBN 978-82-8211-279-6.
    13. Petrow 1974, p. 72.
    14. Petrow 1974, p. 89.
    15. Petrow 1974, p. 90.
    16. McDouglas 1997, pp. 211–212.
    17. Yale Law School 2008.
    18. Ziemke 1960, p. 68.
    19. Ziemke 1960, p. 59.
    20. Ziemke 1960, pp. 66–67.
    21. Ziemke 1960, pp. 67–68.

    Bibliography
    • Booth, Owen (1998). The Illustrated History of World War II. London: Chartwell Books, Inc. ISBN 978-078581-016-2.CS1 maint: ref=harv (link)
    • Hooton, Edward R. (2007). Luftwaffe at War; Blitzkrieg in the West: Volume 2. London: Chevron/Ian Allan. ISBN 978-1-85780-272-6.CS1 maint: ref=harv (link)
    • McDouglas, Myres (1997). The International Law of War:Transnational Coercion and World Public Order. New York: Springer. ISBN 978-079232-584-0.CS1 maint: ref=harv (link)
    • Outze, Børge (1962). Danmark under anden verdenskrig (in Danish). Copenhagen: Hasselbalch. ISBN 87-567-1889-6.CS1 maint: ref=harv (link)
    • Petrow, Richard (1974). The Bitter Years; The Invasion and Occupation of Denmark and Norway, April 1940-May 1945. London: William Morrow & Co. ISBN 978-068800-275-6.CS1 maint: ref=harv (link)
    • Schrøder, Hans A. (1999). Angrebet på Værløse flyveplads den 9. april 1940 : flyveren Vagn Holms dagbog fra den 8. og 9. april suppleret med en omfattende dokumentation (in Danish). Denmark: Flyvevåbnets bibliotek. ISBN 87-982509-8-1.CS1 maint: ref=harv (link)
    • Zabecki, David T. (2014). Germany at War: 400 Years of Military History. London: ABC-Clio Inc. ISBN 978-1-59884-980-6.CS1 maint: ref=harv (link)
    • Ziemke, Earl F. (1960). "The German Decision to Invade Norway and Denmark". Command Decisions. United States Army Center of Military History. Retrieved 18 August 2016.CS1 maint: ref=harv (link)

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