Before the Occupation of Denmark by Germany in 1940, Prior encouraged the Danish government to increase the strength of the army. These requests, however, were not accepted by the majority of the Danish parliament, who feared that increased military strength might provoke Nazi Germany.
When Germany invaded Denmark in 1940, he argued that the Danish army should actively defend the country, even when Germany threatened through the dropping the OPROP! leaflets to bomb the capital of Copenhagen. However, the Danish government did not agree to this, due to concerns that major Danish cities like Copenhagen might suffer the same destruction that other cities like Warsaw had just experienced during the German invasion of Poland. The government was also well aware that Denmark's position was untenable; it was too small and too flat to hold out against the Wehrmacht for a sustained period.
Prior continued as Commander-in-Chief of the Danish Army during the early part of the German occupation, and worked actively to prevent the Danish army from becoming involved on the German side during World War II. He resigned as Commander-in-Chief in October 1941 and was replaced by Lieutenant General Ebbe Gørtz.
Selected works
Operationerne paa Østfronten i 1914. Studier over Verdenskrigen (in Danish). Copenhagen: Det Krigsvidenskabelige Selskab. 1919.
Operationerne paa Østfronten i 1915. Studier over Verdenskrigen (in Danish). Copenhagen: Det Krigsvidenskabelige Selskab. 1921.
Generalløjtnant A.A.B. Kühnel: En dansk officers liv og gerninger (in Danish). Copenhagen: Ejnar Munksgaard. 1942.
Bjerregaard, W. (24 June 1946). "Generalløjtnant W. W. Prior". krigsvidenskab.dk (in Danish). Retrieved 9 September 2020.
Clemmesen, Michael Hesselholt (1982). Jyllands landforsvar fra 1901 til 1940 (in Danish). Copenhagen: Det Krigsvidenskabelige Selskab. ISBN87-981346-0-4.
Grøn, Ole; Clemmesen, Michael H. (2014). "Skyggerne på væggen: Et forsøg på delvis rekonstruktion af efterretningstjenesten i og fra Sønderjylland fra 1920 til ca. 1950". Fra Krig og Fred (in Danish) (1): 86–180.