Oscarsborg Fortress, an island stronghold built in the mid–nineteenth century and Oslo’s last major line of defense

From Last Hope Island by Lynne Olson.  It is a story of the leadership and armies in exile in England during German occupied Europe in World War II.  The Polish pilots during the Battle of Britain and the Free French have probably received the greatest attention in general histories but the story is broader and more complex than that and Olson tells it well.

As a child, I heard this particular story in Norway, of the antique harbor fortress to Oslo, firing one of their ancient canon at the invading German occupation fleet.  The story went that the Norwegian resistance made the effort more as a hopeful gesture than out of any realistic naval prospect.  Against all odds, one of the shots struck the ammunition locker on the lead German cruiser and the ship sank in short order.  It was told that no recovery efforts were made after the war because the sunken cruiser, the Blücher, had all the occupation plans and there were concerns that recovering any documentation might complicate the post-war reconciliation between the few collaborators and the many Norwegian resistance fighters.  

By Olson's account, this hearsay version I heard was substantially correct. 

Aboard the German heavy cruiser Blücher, General Erwin Engelbrecht, who commanded the attack force heading for Oslo, reviewed his orders with his subordinates. In just a few hours, more than a thousand troops, equipped with minutely detailed maps and photographs of the Norwegian capital, were to disembark from the Blücher in Oslo’s harbor. Their assignment was to slip into the sleeping city and storm government buildings, the state radio station, and the royal palace. Before noon, King Haakon, Crown Prince Olav, and the rest of the royal family would be under arrest and the Norwegian government under German control. A band, also on board the Blücher, would play “Deutschland über Alles” in the city’s center to celebrate Germany’s triumph, while German military officials took over administration of the country and its two most important material assets—its merchant marine and its gold.

When a Norwegian patrol boat spotted the flotilla and had the temerity to issue a challenge, the boat was machine-gunned and sunk. Farther up the fjord, two small island forts, alerted by the patrol boat, also fired on the ships, but the heavy fog made accurate sighting impossible and the vessels swept on untouched. Shortly before 4 A.M., the convoy approached Oscarsborg Fortress, an island stronghold built in the mid–nineteenth century and Oslo’s last major line of defense. The Blücher’s captain was as unperturbed by the sight of the fortress as he had been by the pesky patrol boat. On his charts and maps, Oscarsborg was identified as a museum and its two antiquated cannons described as obsolete.

The maps and charts were wrong on both counts. The fortress was operational, and so were the old cannons, fondly called “Moses” and “Aaron” by their crews. The fog lifted a bit, and as the darkened silhouettes of the ships came into view, a searchlight on the mainland suddenly illuminated the Blücher. Moses and Aaron erupted at point-blank range, their shells crashing into the 12,000-ton heavy cruiser. One shell smashed into the Blücher’s bridge, destroying its gunnery and navigational controls, while another slammed into a storeroom filled with aviation fuel. Shore batteries also began firing. Within seconds, the Blücher was ablaze, the flames leaping high into the air, burning off the fog, and lighting up the snow-covered banks of the fjord.

With a great roar, the ship’s torpedo magazine exploded, and less than an hour later, the Blücher, commissioned only seven months before, rolled over on its side and sank. Nearly one thousand men went down with her, including most of the elite troops assigned to capture the royal family and government officials. General Engelbrecht was one of the several hundred survivors who escaped the burning oil covering the fjord’s surface and swam frantically to shore.

Throughout that day—April 9, 1940—Hitler’s audacious, meticulously planned invasion of Denmark and Norway had gone almost exactly as planned. By early afternoon, virtually all the Führer’s major objectives along the 1,500 miles of Norwegian coastline had been taken—all, that is, except Oslo, the political, economic, and communications center of Norway and the key to the operation’s eventual success.