Nazi Germany invaded Denmark on 9 April 1940, during the Second World War. The attack was a prelude to the invasion of Norway (, 9 April – 10 June 1940).

Denmark's strategic importance was limited. The invasion's primary purpose was to use Denmark as a staging ground for operations against Norway, and to secure supply lines to the forces about to be deployed there. An extensive network of radar systems was built 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, and after a short battle were forced to surrender. After less than two hours of struggle, Danish Prime Minister Thorvald Stauning ended the opposition to the German attack, for fear that the Germans would bomb Copenhagen (København), as they had done with Warsaw during the invasion of Poland in September 1939. Due to communication difficulties, some Danish forces continued to fight, but after a further two hours, all opposition had stopped.

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

Background The attack on Denmark was part of Operation Weserübung Süd, Germany's plan for the invasion of Norway. Its main purpose was to secure the iron ore that shipped from Narvik. To capture Norway, the Germans had to control the port outside Aalborg in northern Jutland (Jylland). The Kriegsmarine high command approved of occupying Denmark to extend the German sea-defence network northward, making it harder for British ships to outflank it from the north when attacking ships in the Atlantic. Norway's fjords also provided excellent bases for German submarines in the North Atlantic. The Germans presented the invasion as an act of protection against a supposed imminent attack by the United Kingdom and France.

German plan of attack

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 Aalborg airfields, a surprise landing of infantry from naval auxiliaries at Copenhagen (København), and a simultaneous ground assault across the Jutland (Jylland) peninsula. On 4 April, Admiral Wilhelm Canaris, chief of the Abwehr and involved in the German resistance to Nazism, warned the Danes of an imminent invasion.

Skirmishes Although the Royal Danish Army was warned of the attack, it was denied permission to deploy or prepare defensive positions as the Danish government did not want to give the Germans any provocation for their actions. Only small and scattered units of the frontier guard and elements of the Jutland (Jylland) 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.

Fighting in Jutland The Danish border was breached at Sæd, Rens, Padborg, and Krusaa (Kruså) at 04:15 on the 9th. 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.

Eastern flank Lundtoftbjerg 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 cannons 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 Aabenraa. About to the north, a bicycle platoon prepared a 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 captured. The Germans lost two armoured cars and three motorcycles, while the Danes suffered one dead and one wounded.

Another German column reached Hokkerup a few kilometres east of Lundtoftbjerg at 05:30. They 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 remaining armoured cars to withdraw. The Germans set up a 37 mm gun away, but it managed to fire only one round before being knocked out by two rounds from a 20 mm gun. Hand-to hand combat ensued in which one Dane was killed and three wounded, one fatally. With air support, the 100 or so Germans managed to surround and capture the Danish unit at 06:15.

Bjergskov

north of Lundtoftbjerg, one motorcycle and two bicycle platoons arrived at Bjergskov at around 05:00. Under 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. Their tanks pushed the roadblock aside and opened fire. One gun returned fire until a tank drove over it. The gunner attempted to run for cover in the woods but was killed when a German aircraft strafed the road. The second gun malfunctioned. The Danes tried to escape on motorcycles but the Germans surrounded them with armoured vehicles and captured them. A further four Danish soldiers were wounded, while one German armoured car was damaged.

Central thrust

Bredevad

In an encounter between Danish and German forces at Bredevad, north of the border, a German vanguard of four armoured cars approached the village. The Danes arrived at 6:30 AM 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 300 meters (yards) out, knocking out the lead armoured car and killing its driver. A short skirmish followed. The Danes knocked out three more German armoured cars and 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.

Rabsted A cyclist platoon from Korskro arrived at Rabsted at 6:45. While lying in wait, they managed to capture two German dispatch riders. Learning from them that Bredevad had been taken, they retreated to the northeast via secondary roads.

Aabenraa

As the Danish forces at Søgaard army camp prepared to pull back north to Vejle, where the main force of the Jutland (Jylland) Division was preparing for battle, a short skirmish occurred at Aabenraa 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. They rendezvoused with a bicycle platoon from Stubbæk Skov, which had suffered one killed and three wounded by German aircraft. The Danish CO ordered them to northern Haderslev.

Haderslev

Haderslev had a garrison of 225 men of the Jutland (Jylland) Division under Colonel A. Hartz, which 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. Bolstered by retreating units, approximately 400 Danes defended the town. Three roadblocks were set up: one with dumping wagons, the other two from spare lumber.

At about 07:50 on the southern outskirts of Haderslev, a Danish 37 mm anti-tank gun with a crew of five attacked the approaching armour. Two German tanks lined up adjacent to one another and opened fire. The Danes landed all three of their shots—one in a tank's tracks—but two of the gun crew were killed and the rest 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. A Danish soldier was killed and two were wounded, but the Germans were effectively pinned down. The fighting continued for ten minutes until the order to surrender was received from Copenhagen (København) by telephone. The Germans were then allowed to proceed into Haderslev, but the Danish garrison stationed there had not received the order to surrender and fired on them. Two German tanks and a motorcycle proceeded unsuspecting towards the barracks, which were defended by the anti-tank unit from Lundtoftbjerg. They 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.

Western flank

Abild and Sølsted The first fighting in Western Jutland (Jylland) occurred against the Tønder garrison, which was dispatched to Abild and Sølsted. At Abild, a Danish 20 mm gun crew knocked out two German armoured cars of the German 11th Motorised Regiment before pulling back. At Sølsted, a Danish anti-tank unit consisting of fewer than 50 men set up a defensive position with a 20 mm gun on a road. When a force of the German 11th Motorised Regiment approached, the Danes opened fire as soon as the first German armoured car came within range. The first vehicle was knocked out and ended up 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 they became bogged down. Seeing that his attack was failing, the German regimental commander radioed for support and three German Henschel Hs 126 aircraft soon appeared. They 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.

Airborne landings At approximately 05:00, history's first paratrooper attack took place. 96 Fallschirmjäger jumped from nine Junkers Ju 52 transport aircraft to secure Storstrøm Bridge, connecting the island of Falster with Zealand (Sjælland) and the coastal fortress on Masnedø island. The elite German troops expected heavy fighting around the fortress, but much to their surprise, only two privates and an officer were found inside. The landing opened the way for a battalion of the 198. Infanterie-Division to advance on Copenhagen (København) by land.

Two hours later, a platoon of paratroopers from the 4th battalion of Fallschirmjäger Regiment I landed in Aalborg, the main city of northern Jutland (Jylland), to secure Weserübung Süd's primary target: the airfield at Aalborg, to be used as a stepping-stone for the invasion of Norway. The Fallschirmjäger encountered no resistance, and in less than an hour German aircraft were landing there in huge numbers. More than 200 landings and takeoffs were recorded on the first day, most of them transporting troops and fuel to Fornebu Airport in Norway.

In Esbjerg, a 75mm anti-aircraft gun damaged a German aircraft.

Naval landings

In order to capture the connections between Jutland (Jylland) and Zealand (Sjælland), the Kriegsmarine landed more troops from the 198th Infantry Division at Funen (Fyn).