Oscarsborg Fortress

Drøbak, Norway

The narrows at Drøbak, called Drøbaksundet, is a natural point for the naval defence of Oslo, the capital of Norway. The first defences were constructed during the reign of Christian IV of Denmark and Norway and were ready in 1644. The fortifications were however not involved in battle during the Hannibal War. After the war the fortifications were dismantled, and only resurrected for a short period during the 1814 war with Sweden.

Around 1830 the discussion started for a renewed fortification of the Drøbak Narrows and the first stage was ready in 1848, the next in 1853. The name of the fortress was given by royal resolution on 23 August 1855 after a visit by the Swedish-Norwegian King Oscar I.

By the end of the 19th century the art of war developed rapidly and the new fortress was soon obsolete. The tension was also growing between the two countries in the union and so the Norwegians decided to upgrade the fortress. From 1890 new improved German guns were installed, an underwater barrier was built in 1874–79, and an underwater torpedo battery was constructed. The main armament was three 28 cm calibre guns manufactured by Krupp. There were also a number of guns with smaller calibres on the mainland. An underwater barrier went from the main islet of Kaholmen and south-west to Hurum on the western side of the fjord, thus making it impossible for large vessels to sail west of the fortress.

Having been constructed in 1898–1901, and taken into service on 15 July 1901, the underground torpedo facility remained one of the few Norwegian defence installations unknown to German military intelligence at the point of the 1940 invasion. The battery was one of two in Norway and it was designed to launch its torpedoes from under the water level. At Oscarsborg the torpedo battery is a concrete construction inside a cave mined into the rock of the North Kaholmen island.

When Norway was invaded on 9 April 1940, all of the fortress' armament was over 40 years old, and of German origin. Both the guns and the torpedo battery worked flawlessly when Oscarsborg encountered one of the German invasion flotillas; they sank the heavy cruiser Blücher, and threw back the German naval force heading for Oslo, thus managing to save the Norwegian King and government from being taken prisoner. The fortress was returned to Norwegian control on 12 May 1945 when Captain Thorleif Unneberg took command of the fortifications and raised the Norwegian flag following the capitulation of all German forces in Norway four days earlier.

During the Cold War Oscarsborg formed a last line of defence for the capital city, with the underground torpedo battery remaining secretly active up until 1 January 1993, having been modernized in the 1980s. After the deactivation of the last weapons systems, the remaining military activity on Oscarsborg consisted of the Coastal Artillery officer training programme. The officer school was officially shut down in 2002. The fortress is now largely a civilian resort and attraction, open for visitors. The scenic surroundings is much used for conferences and excursions. Visitors take a short motor launch trip from Drøbak.



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Founded: 1846-1855
Category: Castles and fortifications in Norway


4.6/5 (based on Google user reviews)

User Reviews

Jorge Bernardo (2 months ago)
I've just passed this island fortress on my way in and out the Oslo fjord on a big cruise ship and it really seemed totally impregnable. I got to know it sunked a German heavy cruiser during WWII and I guess it would sunk anything else trying to pass through, as it crosses fire with mainland based batteries. Since 2003 the island fortress has been considered with no military value anymore and was, therefore, opened to the public as a park.
Abel Fernandes poio (3 months ago)
This place was amazing and awesome. I enjoyed the fort and there was a lot of interesting stuff to see. This is a real deal fort. I loved it. ???❤️♥️♥️
Simen (6 months ago)
Very nice Island with lots to explore. Good ferry ⛴️ connections.
Claire Pearmund (7 months ago)
Visited 28th Aug and was not the best experience. First, you need to get a bus from Oslo (45min) to Drobak as the boat direct from Oslo does not run midweek even though the sign at the bock says otherwise. The small boat from Drobak was pleasant but didn't have any guides like the tourist sign said (ask for a map on the boat!!) The fortress had NO refreshments to buy, so take food/drink (we did not). There were 2 restaurants (like I had read), but both shut. The best part was a five minute basic movie explaining how the Blucher was sunk, but then, for us, it didn't go into enough detail. We were also disappointed that the display boards in the main museum were hit and miss with English translation some had it and some didn't. There is a guided tour you can do but again only peak and when at the fortress there is a sign saying you can book in advance for one (very helpful) so we didn't get to see the torpedo as this is with a guide only (from what we could gather)
Hans-Kristian Nordhaug (7 months ago)
Old Fortress in the Oslo fjord. It's location is were the fjord is at it's thinnest. It was from thos location that Blucher was sunk on 9th of april 1940. Which then helped the royal family to get out of Norway. Great place to learn, very scenic. Also nice for the kids.
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