OSLO (Reuters) — U.S. Navy dolphins will take part in a NATO exercise to find some of the 80,000 mines and other munitions rusting off Norway's coast since Germany's World War II occupation, officials said on Friday.

The "Blue Game," the name given to the exercise, will take place from April 23 to May 11. It follows a similar two-week exercise in the Baltic Sea last year in which 83 mines were cleared, according Rune Hausken, commander of the mine-clearance diving team for south Norway.

"It will be the biggest mine-clearing exercise off Norway ever," Hausken said of the exercise to take place off the south coast of Norway.

Four dolphins, trained to use their own natural sonars to find mines on the seabed and then attach a marker buoy, will take part with divers from the United States, Germany, Britain, Canada, the Netherlands, Denmark, Belgium and Norway.

"Dolphins have never been used to locate mines off Norway," Hausken told Reuters, adding U.S. dolphins had been used last year in the Baltic Sea to find Soviet-era mines.

"In the Baltics the seabed is very plain and sandy. Here the fjords are deep and more rocky," said Per Hole, a Norwegian navy commander and mine warfare officer.

The Nazis deployed an estimated 80,000 mines along the Norwegian coast during World War Two as well as other ordnance including torpedoes and grenades.

The explosives still pose a threat to sports divers and fishermen. In neighboring Denmark, poisonous mustard gas recently leaked from one container fished up from the seabed.

The exercise aims to train NATO divers in finding mines and is likely to find only a tiny fraction of the mines.