Since launching in 2003, Losharik has undertaken some dangerous missions of national importance. In 2012 the submarine and an accompanying vessel drilled to a depth of almost two miles on the Arctic seabed in order to retrieve soil samples and identify the outer limits of Russia’s continental shelf.

Many of the vessel’s other duties are shrouded in mystery, but could involve trials of new sensors and weaponry. “It’s a very useful submarine,” Polmar said.

Research submarines such as Losharik arguably are more important than ever for Russia’s strategic plans. The Russian navy for years clung to its position as one of the world’s most powerful fleets largely by refurbishing Cold War-vintage surface warships.

But those ships and their support infrastructure are becoming harder to maintain.