The German High Command planned a combined assault on Denmark to overrun the country as swiftly as possible. It included an airborne assault on the Aalborg airfields, a surprise landing of infantry from naval auxiliaries at Copenhagen, and a simultaneous ground assault across the Jutland peninsula.[12] On 4 April, Admiral Wilhelm Canaris, chief of the Abwehr and involved in the German resistance to Nazism, warned the Danes of an imminent invasion.[13]