submarine submarine

Peter Madsen's private submarine sits on a pier in Copenhagen harbor. The Danish inventor faces a murder charge after Swedish journalist Kim Wall died aboard the sub under mysterious circumstances last month. Jens Dresling/AP hide caption

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Jens Dresling/AP

Peter Madsen's private submarine sits on a pier in Copenhagen's harbor. Danish police have identified a headless, limbless torso that washed ashore Monday as that of Kim Wall, the journalist who joined Madsen on his sub earlier this month to report a story. Jens Dresling/AP hide caption

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Jens Dresling/AP

Helicopter belonging to the Netherlands participates in NATO's Dynamic Mongoose anti-submarine exercise in the North Sea, off the coast of Norway, on May 4, 2015. MARIT HOMMEDAL/AFP/Getty Images hide caption

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MARIT HOMMEDAL/AFP/Getty Images

The Swedish corvette HMS Visby is engaged in a military operation on the fifth day of searching for a suspected foreign vessel in the Stockholm archipelago, Mysingen Bay, Sweden, on Oct. 21. Swedish authorities say they have proof it was a foreign sub but don't know the nationality. Fredrik Sandberg/EPA/Landov hide caption

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Fredrik Sandberg/EPA/Landov

Swedish corvette HMS Stockholm patrols Jungfrufjarden in the Stockholm archipelago, Sweden, on Monday. Swedish authorities say they've detected "foreign underwater activity" thought to be a possible Russian submarine. Anders Wiklund/EPA/Landov hide caption

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Anders Wiklund/EPA/Landov