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.

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

[12] 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.

Only small and scattered units of the frontier guard and elements of the Jutland (Jylland) division were available to meet the land invasion.

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.

About 1.5 kilometres (0.93 mi) 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.

When the Germans ignored this, the Danes opened fire from 300 meters (yards) out, knocking out the lead armoured car and killing its driver.

[14] As the Danish forces at Søgaard (Søgård) 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 (Åbenrå) as the anti-tank platoon from Lundtoftbjerg attacked 15 or so pursuing German vehicles.

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.

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.

The elite German troops expected heavy fighting around the fortress, but much to their surprise, only two privates and an officer were found inside.

[14] 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).

[23] At the same time, troops supported by the battleship Schleswig-Holstein landed in Korsør and Nyborg, cutting off connections between Funen (Fyn) and Zealand (Sjælland).

At 04:20[27] the 2,430 ton minelayer Hansestadt Danzig, with an escort of the icebreaker Stettin and two patrol boats, entered Copenhagen (København) harbour with battle flags flying.

The newly appointed Danish commander ordered a warning shot to be fired, but the recently arrived recruits could not operate the gun.

[28] After landing a battalion of the 198th Infantry at 05:18, German forces captured the 70-strong garrison of Kastellet, the headquarters of the Danish Army, without a single shot.

[23] Upon their arrival at Amalienborg, the German infantry encountered fierce resistance from the on-duty company of the King's Royal Guard.

The situation then quickly escalated as Danish reinforcements swiftly arrived from Rosenborg Barracks, bringing with them multiple 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 dogged resistance of the Royal Guard gave King Christian X and his ministers time to confer with the Danish commander-in-chief General Prior.

[29] During the discussions, several formations of Heinkel He 111 and Dornier Do 17 bombers from Kampfgeschwader 4 roared over the city dropping OPROP!

Faced with the explicit threat of Luftwaffe bombing Copenhagen's civilian population, all but General Prior favoured surrender.

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 panzers.

The Danish government ordered a ceasefire at 06:00, and formally capitulated at 08:34[23] 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 successfully expel 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 inevitably arrive soon after.

In anticipation of the German invasion, they had prepared to disperse to airfields around the country, but this had not been accomplished by 05:25 when Luftwaffe aircraft appeared over the airbase.

They destroyed 11 aircraft and badly damaged another 14 as they taxied to take-off, wiping out most of the Danish Army Air Service in one action.

Colonel Helge Bennike [da], commander of the 4th 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.