Operation Weserübung was the German assault on the neutral nations of Denmark, Norway and Sweden during World War II. That attack triggered the Norwegian Campaign, that would be won by the Germans. The operation name means "the Weser Exercise", Weser being a German river. It was planned by the German GeneralNikolaus von Falkenhorst, at the request of Hitler.
At 4:15 a.m. in the morning local time, the "Weser Time" by April 9, 1940, the "Weser Day", Germany invaded Denmark and Norway, soposedly to protect them from a possible attack from France and England.