Did the sinking of the Blücher in 1940 affect the outcome of the war?

In the conclusion to this forensically detailed book, the authors, one a naval historian, the other a retired naval officer who served in the Oscarsborg fortress outside Oslo – the cornerstone of the story – during the Cold War, ask: ‘What would have happened if Hitler had not unleashed his dogs of war on Norway in April 1940, or if Blücher had not been sunk?’ To which of course they reply that we shall never know.

They do, however, posit that in the worst case, Churchill might not have become prime minister, and the evacuation from Dunkirk would not have been the success it was. That’s not entirely new, but it’s not always remembered – Dunkirk especially – or at least not outside the authors’ Norway. The Christmas tree in Trafalgar Square isn’t merely a thank you.

Operation Weserübung, the German invasion of neutral Denmark and Norway, began in the early morning of 9 April. It wasn’t war, said Berlin, but ‘military measures for the protection of the neutrality of Denmark and Norway’. The claim was faintly plausible, as Britain had been trying vigorously to mount a naval blockade to weaken German industry, which was dependent on the import of iron from northern Sweden through the Norwegian port of Narvik. The claim didn’t wash as far as Denmark was concerned, but invading Norway without first neutralising Denmark would have been perilous.

While Denmark quickly capitulated, however, Norway fought. Her forces had been mobilised for some time, not least because of the Soviet threat following the invasion of Finland, and the implications of the Molotov-Ribbentrop pact. Hitler had expected the Norwegian government to surrender, but if not, Vidkun Quisling, the head of the fascist Nasjonal Samling, would stage a coup d’état.

As with Denmark, the key to success would be a coup-de-main operation against the capital, putting the king and his government in the bag.