Operation Weserübung (German: Unternehmen Weserübung [ˈveːsɐˌʔyːbʊŋ]) was the code name for Germany's assault on Denmark and Norway during the Second World War and the opening operation of the Norwegian Campaign. The name comes from the German for "Operation Weser-Exercise", the Weser being a German river.
In the early morning of 9 April 1940 (Wesertag, "Weser Day"), Germany invaded Denmark and Norway, ostensibly as a preventive manoeuvre against a planned, and openly discussed, Franco-British occupation of Norway known as Plan R 4. After the invasions, envoys of the Germans informed the governments of Denmark and Norway that the Wehrmacht had come to protect the countries' neutrality against Franco-British aggression. Significant differences in geography, location and climatebetween the two nations made the actual military operations very dissimilar.
The invasion fleet's nominal landing time, Weserzeit ("Weser Time"), was set to 05:15.