Oscarsborg Fortress


Late in the evening of April 8, the German cruiser Blücher approached with his companions Lützow and Emden the inlet to the Oslo fjord. This force was part of Operation Weserübung, the German attack on Denmark and Norway, and its target was Oslo. Throughout the night between April 8 and 9, Blücher sailed by following through the Oslo fjord, but they had been discovered and encountered sporadic resistance from various coastal batteries. The darkness and the dense fog that prevailed at the time made it difficult for both parties to see each other so Blücher continued at low speed towards Oslo.

Shortly after four o’clock in the morning, the force approached Oscarsborg Fortress, which was located in the middle of the narrow Droebak’s strait about four miles south of Oslo. An old-fashioned fortress that had been inaugurated in 1855 by the then Swedish/Norwegian king Oscar the first. The fort’s armament was also not considered able to offer any significant resistance, but the fortress commander Colonel Birger Eriksen was of a different opinion. Despite ambiguities as to whether enemy ships were discovered, he ordered at 04:21 two of the fortress’ three 28 cm guns to open fire on Blücher.

Two shots were fired, both of which seriously damaged Blücher, she started to burn and difficault to manouver. In addition to the cannons on the fortress, smaller coastal batteries at Droebak opened fire on Blücher, Lützow and Emden. Blücher, who for some reason had entered the fjord without being ready for battle, could only answer the fire with it’s anti-aircraft guns. But the Germans had difficulty in the darkness and fog to locate where the shots came from and tried to increase the speed to thereby escape. Blücher then ended up in the firing line of a torpedo battery at the fortress which at 04.30 fired two torpedoes that both hit Blücher. 

Blücher, who was already badly damaged, was hit by a heavy blow and the commander Oskar Kummetz realized that the ship could no longer be saved. At 06.22, Blücher sank outside Askholmarna just over two kilometers north of Oscarsborg Fortress. Between 650 – 850 Germans followed her about 90 meters into the depths. The other two ships Lützow and Emden were forced to turn around, especially bad was it for Lutzow who had been hit several times by the coastal artillery cannons. The German attempts to take Oslo by sea had thus failed and gave the Norwegian government time to flee. Between 08.00 and 18.00 on April 9, the fortress was subjected to intense bombing by Luftwaffe and on April 10, Birger Eriksen surrendered.

Current status: Preserved with museum (2012).

Address: Oscarsborgs fästning, 1443 Frogn.

Get there: Ferry from Droeback.

My comment:

One might wonder why the Germans did not neutralize the fortress before Blücher approached to avoid the disaster that followed. But one likely reason is probably that the Germans had underestimated the norwegians and the sight of the german navy would cause the fortress to capitulate or be abandoned. But this was a characteristic of the Germans who more than once underestimated their opponent’s will, resources and abilities to fight back while their own resources and abilities were often overestimated.

Follow up in books: Greene, Jack, Massignani, Alessandro: Hitler Strikes North: The Nazi Invasion of Norway & Denmark, April 9, 1940 (2013).