4 hours.
On April 9, 1940, the German "Operation Withersburg" began. 1000 German troops landed at the port of Copenhagen and met a Danish royal escort. The two sides engaged in a fierce battle. Before a few shots had been fired, several German He-111 and DO17 bombers had circled over the Danish capital, and German follow-up troops had landed from Silan Island and Falst Island. At the same time, the German army began to persuade the Danish king to surrender.
Christian X, the old king of Denmark, was over 50 years old at that time, and Denmark's military strength was far less than that of Germany. After the discussion of the cabinet, Denmark chose to surrender, and ordered the convoy that was still fighting to give up resistance immediately.
At more than 8 o'clock that morning, the Danes who had just woken up heard the amazing news on the radio that "Denmark has accepted German protection, and the Danish people must not resist". When the Danish people were still in a muddle, the German army took control of Denmark within two days and was not resisted by the Danish army. Instead of dissolving the cabinet, Germany fostered pro German forces and sent German "commissioners" to Denmark to "guide" the work of the old king.
In the whole operation, the German army made Denmark surrender in only four hours, and only nine Danish soldiers were killed. During the German occupation, six civilians rebelled against Germany and were killed. In other words, during the Nazi German invasion of Denmark, Denmark only sacrificed 15 people.