Oscarsborg shows what Norway's unmobilized defenses could still do

In this interpretation, Norway's government failed to mobilize its reserves promptly despite warning from the invasion of Denmark. Oscarsborg Fortress nevertheless sank Blücher and delayed the Oslo force long enough for the monarchy and government to escape. In the confined fjords, even old guns and torpedoes remained dangerous because German ships had to enter their effective range. Fully crewed defenses at Oslo, Narvik, and elsewhere might have imposed a severe early defeat on Germany, though the forces committed there were probably too small to change the fall of France. In a hypothetical scenario explored through simulations, retaining Norway also gives the Allies better bomber basing, reduces threats to Arctic convoys, constrains U-boat access to the North Atlantic, and disrupts the Swedish iron-ore route. Alerted defenders ashore and a Royal Navy intervention behind the German expedition could also have trapped the landing force between them.