During the ‘phoney war’ there was a limited range of material about military activity that could be used for propaganda purposes. Yet the war in the North Sea was anything but phoney, with increasing numbers of ships being sunk. Both sides were responsible for laying enormous numbers of mines in order to restrict access to their own ports except through particular channels, and more generally to hinder the free movement of hostile ships and submarines. British minelaying operations were responsible for sinking a number of U-Boats and German ships, see for example Operation Wikinger and the fate of U-50. This Movietone Newsreel demonstrates the enormous effort and resources that were needed to lay effective minefields.
British minelaying in the North Sea
Earlier in the war: HMS Grenville sunk, the Russians attack again in Finland
Later in the war: Admiral Dönitz inspects a German U-boat crew