The 'Campaign for Denmark' was the German invasion of Denmark more formally known as part of 'Weserübung Süd', and as such the prelude to the 'Weserübung Nord' German invasion of Norway (9 April 1940).

For Germany, the strategic significance of Denmark was strictly limited, for the undertaking’s primary purpose was merely to secure Denmark as a staging point for operations against Norway, and to secure supply lines to the forces about to be deployed there. However, the Germans later built an extensive network of radar systems in Denmark to detect British bombers bound for Germany.

The attack on Denmark was a breach of the non-aggression pact Denmark had signed with Germany less than a year earlier. The initial plan was to push Denmark to accept that German land, naval and air forces could use Danish bases, but Adolf Hitler subsequently demanded that both Norway and Denmark be invaded.

Denmark’s military forces were inferior in numbers and equipment to those of Germany, and after a short battle were forced to surrender: after less than two hours of struggle, Danish Prime Minister Thorvald Stauning ended opposition to the German attack for fear that the Germans would bomb Copenhagen, as they had done with Warsaw during their 'Weiss' (i) invasion of Poland in September 1939. As a result of communication problems, some Danish forces continued to fight, but after another two hours, all opposition had come to an end.

Lasting approximately six hours, the German ground campaign against Denmark was one of the shortest military operations of World War II.

The attack on Denmark was part of 'Weserübung', Germany’s plan for the invasion of Norway with the primary purpose of securing the transit of Swedish iron ore to Germany during the winter months in which the Baltic Sea was frozen, and the Norwegian port of Narvik was the only alternative point of shipment. To capture Norway, the Germans had to control the port outside Aalborg (Ålborg) in northern Jutland. The leadership of the Kriegsmarine approved the occupation of Denmark to extend the German sea-defence network farther to the north, thereby making it more difficult for British warships to outflank it from the north when attacking ships in the Atlantic. Norway’s fjords also provided excellent bases for U-boats and warships to launch raiding operations in the North Atlantic. The Germans presented the invasion as an act of self- and Norwegian protection against a supposedly imminent attack by the UK.

The German high command planned a combined assault on Denmark to overrun the country as swiftly as possible. It included an airborne assault on the Ålborg airfields, a surprise landing of infantry from naval auxiliary vessels at Copenhagen, and a simultaneous ground assault into the Jutland peninsula. On 4 April, Admiral Wilhelm Canaris, chief of the Abwehr intelligence service and a committed anti-Nazi, warned the Danes of an imminent invasion.

Responsibility for the Danish element of 'Weserübung Süd' was entrusted to General Leonhard Kaupisch’s Höheres Kommando zbV XXXI, a corps-sized formation comprising Generalleutnant Walter Wittke’s 170^th Division of three infantry regiments and one field artillery regiment as well as supporting elements, Generalleutnant Otto Röttig’s 198^th Division also of three infantry regiments and one field artillery regiment as well as supporting elements, and Oberst Günther von Angern’s 11^th Schützenbrigade of two motorised infantry regiments. The Danish forces were deployed in two divisions: in the islands to the east of the Jutland peninsula was the 1^st Zeeland Division of the Life Guards, three infantry regiments, one guard hussar regiment and two motorised artillery regiments, and farther to the west in the Jutland peninsula was the Jutland Division of four infantry regiments, one dragoon cavalry regiment and one field artillery regiment.

Although the Danish army was warned of the attack, it was denied permission to deploy or prepare defensive positions as the Danish government wished to offer the Germans no provocation for their actions. Only small and scattered units of the frontier guard and elements of the Jutland Division were available to meet the land invasion. Believing the attack was imminent, the troops were placed on full alert at 13.30 on 8 April.

The Danish land border was breached at Sæd, Rens, Padborg, and Kruså at 04.15 on 9 April. With the Kriegsmarine simultaneously landing troops at Lillebælt, Danish troops at the border were cut off at the beginning of the fighting. The alarm was sounded at 04.17, and the first Danish troops were dispatched at 04.35.

After the German easternmost crossing into the Jutland peninsula, the first clash between the Danish army and the invading forces occurred at Lundtoftbjerg, where a Danish anti-tank platoon armed with two 20-mm guns and a light machine gun had taken up positions covering the road. A German column appeared at 04.50, and the 20-mm cannon opened fire on the armoured cars while the machine gun took aim at the motorcyclists. A fire started in a nearby barn, filling the air with smoke and hindering the German advance. Eventually the anti-tank platoon was forced to withdraw to Åbenrå. About 1 mile (1.6 km) to the north, a bicycle platoon prepared the defence of a railway bridge, but fire from the armoured cars and strafing fighter aircraft forced them to retreat, and a third of them were taken prisoner. The Germans lost two armoured cars and three motorcycles, while the Danes suffered one men killed and one wounded.

Another German column reached Hokkerup a short distance to the east of Lundtoftbjerg at 05.30, and here encountered a roadblock made with farm equipment, set up only 20 minutes earlier by 34 Danish soldiers. The Danes knocked out the three leading armoured cars, forcing the Germans to pull back. The Germans set up a 37-mm gun 330 yards (300 m) away, but this fired only one round before being knocked out by two rounds from a 20-mm cannon. Hand-to hand combat ensued in which one Dane was killed and three more were wounded, one fatally. With air support, the 100 or so Germans managed to surround and capture the Danish unit at 06.15.

Some 4.3 miles (7 km) to the north of Lundtoftbjerg, one motorcycle and two bicycle platoons arrived at Bjergskov at around 05.00. Under the command of Lieutenant Colonel S. E. Clausen, the motorcycle troops set up a roadblock with two 20-mm guns while the remaining platoons spread out in the woods. A German column arrived at 06.30, and its tanks pushed the roadblock aside and opened fire. One of the Danish guns returned fire until a tank drove over it. The gunner attempted to run for cover in the woods but was killed when a German aeroplane strafed the road. The second gun malfunctioned. The Danes tried to escape on motorcycles but the Germans surrounded them with armoured vehicles and took them prisoner. Another four Danish soldiers were wounded, while one German armoured car was damaged.

In the Germans' central thrust, during an encounter between German and Danish forces at Bredevad, 6.2 miles (10 km) to the north of the border, a German vanguard of four armoured cars approached the village. The Danes arrived at 06.30 and, without time to build a roadblock, took cover in a garden. A machine gun and a 20-mm cannon, manned by one and a half platoons, fired warning shots. When the Germans ignored this, the Danes opened fire from 330 yards (300 m) out, knocking out the leading armoured car and killing its driver. There followed a short skirmish in which the Danes knocked out three more German armoured cars and themselves suffered four casualties. At 07.15 a reinforcing German motorised column arrived from Tinglev, cutting off the Danes and forcing them to surrender. Two Danes were killed and five were wounded.

A cyclist platoon from Korskro arrived at Rabsted at 06.45 and, while lying in wait, captured two German despatch riders. Learning from them that Bredevad had been taken, the Danish platoon retreated to the north-east via secondary roads.

As the Danish forces at Søgård army camp prepared to pull back northward to Vejle, where the main force of the Jutland Division was preparing for battle, a short skirmish occurred at Åbenrå as the anti-tank platoon from Lundtoftbjerg attacked 15 or so pursuing German vehicles. After disabling a German tank, the rearguard pulled back to Knivsberg, where it rendezvoused with a bicycle platoon from Stubbæk Skov, which had suffered one man killed and three wounded by German aircraft. The Danish commanding officer ordered the combined party to move to northern Haderslev.

Haderslev had a garrison of 225 men of the Jutland Division under the command of Colonel A. Hartz, and this detachment defended both the barracks in the town and the road leading to it. Troops in the town mobilised at 07.00 on hearing instructions broadcast from police loudspeaker vans, and bolstered by retreating units, about 400 Danes then defended the town. Three roadblocks were set up: one of tipper wagons, and the other two from spare timber. At about 07.50, on the southern outskirts of Haderslev, a Danish 37-mm anti-tank gun with a crew of five opened fire on the approaching German armour, and in response two German tanks lined up beside each other and opened fire. The Danes landed all three of their shots, one of them in a tank’s tracks, but two of the gun crew were killed and the others were wounded. One tank then drove over the gun. Around the curve on Sønderbro Street, two 20-mm cannon and a machine gun put up resistance at the wagon roadblock. The Germans laid down heavy fire, killing one Danish soldier and wounding two others, but the Germans were effectively pinned down. The fighting continued for 10 minutes until the order to surrender was received from Copenhagen by telephone. The Germans were then allowed to proceed into Haderslev, where the Danish garrison had not received the surrender order and opened fire on the Germans. Two German tanks and a motorcycle proceeded unsuspecting toward the barracks, which were defended by the anti-tank unit from Lundtoftbjerg. This last opened fire, killing the motorcyclist and blowing the tracks off one tank, sending it crashing into a house. However, the Danish garrison capitulated at 08.15 when the order to surrender finally came through. One Danish soldier was killed while defending the barracks, and three civilians were killed in the crossfire.

The first fighting in the western part of Jutland involved the Tønder garrison, which was despatched to Abild and Sølsted. At Abild, a Danish 20-mm knocked out two armoured cars of the 11^th Regiment (mot.) before being pulled back. At Sølsted, a Danish anti-tank unit consisting of fewer than 50 men set up a defensive position on a road with a 20-mm gun. When a force of the 11^th Regiment (mot.) approached, the Danes opened fire as soon as the first German armoured car came within range. This first machine was knocked out and ended in a ditch, while the next continued forward, but pulled back after being hit. It was hit several more times, but was able to fire back. German infantry attempted twice to outflank the Danish positions, but both attempts were met with heavy fire and the Germans became bogged down. Seeing that his attack was failing, the German regimental commander radioed for support and three Henschel Hs 126 single-engined aircraft soon appeared, and bombed and strafed the Danish force until the Danish commander ordered his troops to fall back to Bredebo. In spite of this, no Danish casualties were reported. When the men of the Tønder garrison reached Bredebro, the order to capitulate had been issued and the fighting was over.

At about 05.00, history’s first paratrooper attack took place as 96 Fallschirmjäger of the Luftwaffe jumped from nine Junkers Ju 52/3m three-engined transport aircraft to secure Storstrøm bridge, which connected the island of Falster with Zealand (Sjælland) and the coastal fortress on Masnedø island. The German airborne troops expected heavy fighting around the fortress but, to their considerable surprise, only two privates and an officer were found inside. The landing opened the way for a battalion of Generalleutnant Otto Röttig’s 18^th Division to advance on Copenhagen by land.

Two hours later, a platoon of paratroopers of the 4/1^st Fallschirmjägerregiment landed in Ålborg, the main city of northern Jutland, to secure the primary target of 'Weserübung Süd', namely the airfield at Ålborg for use as a stepping stone in the invasion of Norway. The German paratroopers met no resistance, and in less than an hour German aircraft were landing there in large numbers. More than 200 landings and take-offs were recorded on the first day, most of them transporting troops and fuel to Fornebu airport in Norway.

In Esbjerg, a 75-mm (2.95-in) anti-aircraft gun damaged a German aeroplane.

In order to capture the connections between Jutland and Sjælland, the Kriegsmarine landed more men of the 198^th Division on Funen (Fyn). At the same time, troops supported by the pre-dreadnought battleship Schleswig-Holstein landed in Korsør and Nyborg, cutting off connections between Fyn and Sjælland. Meeting no resistance, the troops at Korsør advanced and reached Copenhagen at 12.00.

Somewhat earlier, at 03.55, the Germans made a surprise attack on Gedser, Denmark’s southernmost city. They made use of the local ferry from Warnemünde, which they crammed with troops. Soldiers swarmed inland and cut telephone lines. Armour and motorcycles followed, and rapidly advanced to captured the Storstrøm bridge in company with the paratroopers.

To ensure Denmark’s quick surrender, the capture of the capital city was considered essential. At 04.20 the 2,430-ton minelayer Hansestadt Danzig, with an escort of the icebreaker Stettin and two patrol boats, entered Copenhagen harbour with battle flags flying. The harbour was covered by the coastal artillery guns of Fort Middelgrund. The newly appointed Danish commander ordered the firing of a warning shot, but the recently arrived recruits could not operate the gun. After landing a battalion of the 198^th Division at 05.18, the German forces captured the 70-strong garrison of Kastellet, the headquarters of the Danish army, without a single shot. Their next target was Amalienborg Palace, residence of the Danish royal family.

On arriving at Amalienborg, the German infantry encountered fierce resistance from the on-duty company of the King’s Royal Guard. The initial attack was repulsed, resulting in three wounded guardsmen and four wounded Germans. The situation then quickly escalated as Danish reinforcements swiftly arrived from the Rosenborg Barracks, bringing with them several Madsen machine guns. The subsequent street fighting around Amalienborg was intense, with particularly ferocious clashes in Bredgade, that ultimately brought the German advance to a complete halt.

The Royal Guard’s dogged resistance gave King Christian X and his ministers time to confer with the Danish commander-in-chief, General­løjtnant William Prior. During the discussions, several formations of Heinkel He 111 and Dornier Do 17 twin-engined bombers of Kampfgeschwader 4 overflew the city dropping propaganda leaflets. Faced with the explicit threat of Luftwaffe bombing of Copenhagen’s civilian population, all but Prior favoured surrender. The argument for surrender was that Denmark’s military position was untenable. Its land and population were too small to hold out against Germany for any sustained period, and its flat terrain would be easily overrun by German armour: Jutland, for example, was wide open to a Panzer attack from Schleswig-Holstein to the south. Unlike Norway, Denmark had no mountain ranges in which a protracted resistance could be mounted. On the other hand, Denmark had significant water obstacles between the Panzers and Copenhagen, a long coastline, and a significant navy that could expect help from the UK and France. A third option, namely that of the government going into exile as the Czechoslovak government had done, was not chosen, in part because the king and the crown prince adamantly refused to leave the crown princess behind as she was in the ninth month of pregnancy and therefore immobile. The Danish government ordered a ceasefire at 06.00, and formally capitulated at 08.34 in exchange for retaining political independence in domestic matters.

The decision to stand down and disarm the Royal Guard caused great frustration among the guardsmen, who firmly believed that they could have expelled the Germans from the capital. This frustration boiled over into an uproar, during which the guardsmen attempted to rearm themselves to launch a direct assault on Kastellet, where the Germans had positioned their temporary headquarters. However, the officers argued that even if the guardsmen were able to drive out the initial German troops, more overwhelming forces would soon, and inevitably, arrive. As a result of these discussions, the guardsmen eventually abandoned their efforts to resist the Germans.

All four squadrons of the Danish army air service was stationed at Værløse near Copenhagen and, in anticipation of the German invasion, had prepared to disperse to airfields around the country. However, this had not been accomplished by 05.25, when Luftwaffe aircraft appeared over the air base. As the German aircraft reached Værløse, one Fokker C.V-E single-engined biplane reconnaissance aeroplane was getting airborne, but was shot down by a Messerschmitt Bf 110 twin-engined heavy fighter flown by Hauptmann Wolfgang Falck at an altitude of 165 ft (50 m). Both men of the Danish crew were killed. Bf 110 warplanes then strafed the base under heavy anti-aircraft fire. They destroyed 11 aircraft and badly damaged another 14 as the latter taxied to take-off, wiping out most of the Danish army air service in one action. The Danish navy air service remained at its bases and escaped damage.

While most of the Danish army obeyed the surrender order, one unit refused. Colonel Helge Bennike, commander of the 4^th Regiment at Roskilde, believed that the order to surrender had been forced on the government by the Germans and that Sweden had also been attacked. Bennike and his unit boarded the ferry in Elsinore to Sweden and went into exile. When the misunderstanding was later cleared up, most of the Danish soldiers stayed in Sweden and later constituted the core of the Danish Brigade in Sweden during 1943.

For propaganda purposes, the Germans sought to present the invasion of Denmark as peaceful so it would be believed that Denmark did not put up any resistance.

One Danish writer has stated that in the archives of the Danish weapons manufacturer DISA, it is claimed that 203 German soldiers were as killed in Jutland. The report was made in co-operation with the German Waffenamt, which gives it weight. This number is also backed up by testimonies from veterans and eyewitnesses. However, the number is considered an exaggeration by most historians.

In 2015, the journal Krigshistorisk Tidsskrift published an article in which a military correspondent summarized key points in the German invasion. He argued that actual German losses were two or three men killed and between 25 and 30 wounded, and that the Danish military suffered a confirmed 16 dead and 20 wounded. Casualties among the civil resistance is not certain, but are given as 10 dead and three wounded.

Other than the front-line casualties, a few aircraft were shot down or crashed, a tug sank after a collision with a German vessel in the Great Belt and the German battleship Schleswig-Holstein was temporarily grounded to the west of Agersø.