The amount of snow in Oslo changes from nothing to substantial amounts back and forth, especially between the scenes at the Royal Palace and the German Embassy.
When the PM calls the King on the night of the invasion the Chamberlain puts the King's uniform on a clothes stand. However in an earlier scene the King is shown in his pyjamas resting his hand on the uniform already hanging on the stand.
The real Battle of Drøbak Sound was much more involved than depicted, the other coastal defense batteries also joining in after the Oscarsborg Fortress had opened fire.
In the final scene we see king Haakon VII in a navy uniform. The curls on his rank insignia curl the wrong/ opposite way.
The rate of fire from the smaller guns on the Blücher is demonstrated to be around 500 rounds a minute; the cyclic rate of fire of the smallest mounted guns was only around 120 rounds a minute.
When the entourage arrives immediately before the King's conversation with Pvt. Seeberg, the car with the registration E664 has a nationality identification plate, with a large N for Norway. These national plates were not introduced until after the War, by the United Nations.