Why was Denmark also invaded in 1940?

Short answer

Because securing the Skagerrak strait, between Norway and Denmark, required seizing Danish airbases. Capturing Aalborg airport was considered especially important for that goal. On 1 March, Hitler issued a directive demanding the invasion of both Norway and Denmark.

Published: November 1, 2026 · Updated: November 1, 2026 · Edited by Above Ten Thousand · Editorial policy

German Mountain troops before departure to CreteNationalmuseet - National Museum of Denmark from Denmark (CC BY SA), vía commons

Danish airbases

To secure the Skagerrak strait, which separates Norway from Denmark, it was necessary to seize the airbases on Danish territory. Within that objective, capturing Aalborg airport was considered particularly important.

One single operation for two countries

The final plan was codenamed "Operation Weserübung" on 27 January 1940. On 21 February 1940 command of the operation was given to General Nikolaus von Falkenhorst. On 1 March Hitler issued a new directive demanding the invasion of both Norway and Denmark, and that same day he signed the official approval for the invasion and occupation of both countries.

The Norwegian backdrop

Germany's first motive for its interest in Norway was Swedish iron ore, on which Germany depended and which was exported through the Norwegian port of Narvik. In February, the British destroyer HMS Cossack boarded the German tanker Altmark in Norwegian waters. Hitler took the incident as a clear sign that the Allies were also willing to violate Norwegian neutrality, which reinforced his decision to invade Norway.