Weserübung — directive of 1 March

Operation Weserübung — the invasion of Denmark and Norway — has been in preparation since December 1939 at the instigation of Admiral Erich Raeder (chief of the Kriegsmarine) and Alfred Rosenberg (who had received Vidkun Quisling in Berlin). The aims are at once to secure Swedish iron ore (the port of Narvik supplies 40% of German steel), to forestall a pre-emptive Allied intervention (the Hankey-Weygand plan exists in London and Paris), and to extend the Kriegsmarine's naval bases for the Battle of the Atlantic.

The Altmark incident of February 1940 — a German vessel intercepted in Norwegian waters by the Royal Navy — has demonstrated Norway's inability to enforce her neutrality. Hitler signs the Weserübung directive on 1 March 1940. Planned trigger date: 9 April 1940, to forestall an Allied intervention projected for 5 April. Command goes to General of Infantry Nikolaus von Falkenhorst, who will have 6 infantry divisions and 2 mountain divisions, escorted by 9 destroyers and 7 cruisers, the whole supported by a Luftwaffe contingent of about a thousand aircraft.

The operation combines amphibious assault (Trondheim, Bergen, Stavanger), parachute drops (Oslo, Stavanger Sola) and a land advance from the German border into Denmark. It is the first major combined-arms maritime-airborne operation of the war. Hitler must arbitrate between Weserübung and Fall Gelb (the western offensive), both within the same time window.