In mid-September 1939, Kaupisch was military governor of Danzig-West Prussia. In late 1939, his staff was adopted to "Höheres Kommando z.b.V. XXXI". It was as head of this command that he April 9, 1940 led Operation Weserübung Süd, forcing the occupation of Denmark. The OPROP! leaflets with a call to refrain from resistance which German planes dropped during the early morning were signed by Kaupisch.