The Avengers (1942)

Horse-race tipster and journalist Colin Metcalfe is picked for the job of foreign correspondent in Norway when Hitler invades Poland. On the way to Norway his boat is attacked by a German U-Boat. However, when he tells the Navy about it, they don't believe him and he is removed from his job. When German forces invade Norway, Metcalfe returns determined to uncover what is going on and stop the Germans in their tracks.