Norwegian and Swedish defence mine sweepers blew up five unexploded World War II-era mines outside Nesodden in the Oslofjord on Wednesday. It’s estimated more than 1,000 sea mines remain in the waterway.
“At the request of the police, in cooperation with Defence, the mine hunting vessels KNM Hinnøy and KNM Karmøy will destroy the mines,” Bjørn Tore Vågnes, the commanding officer of mine sweeper KNM Otra told Norwegian Broadcasting (NRK). He said the routine operation involved divers setting charges next to the mines and exploding them.
The mines were blown up at shallow depths to reduce damage to the sea bed, causing columns of water to jet up into the air (external video, in Norwegian).
Vågnes said about 40,000 Allied and German mines remain after the war. The majority of those in the Oslofjord are British, cylindrical and about three metres long. “In most cases these don’t represent any danger to anyone,” said Vågnes. “When you choose to diffuse old mines it’s often those which lie shallow and are accessible by sports divers, or they can come into conflict with marine installations, for example pipelines.”
He said mine sweepers have to search for mines in the Oslofjord. “We have quite a good overview in the form of historic data which was released after the war, but these here, which were dropped by British planes during the Second World War, we don’t have precise locations for,” Vågnes told NRK. “Then we must go in and see where they physically lie.”