A Russian submarine is to take part in Nato naval exercises for the first time.
It is scheduled to join in next month's undersea rescue exercise off the Spanish coast. The exercise, held every three years, is the largest of its kind in the world and involves multiple subs, warships and search and rescue aircraft.
Nato's and Russia's surface ships co-operate closely as part of the international anti-piracy patrols off the Somali coastline. But no Russian sub has ever taken part in those missions.
During the Cold War, the Soviet Union's massive conventional and nuclear-powered submarine fleets were one of the most dangerous threats faced by Nato.
Military ties between Russia and the alliance have been improving steadily since 2009, despite continuing political disagreements over Georgia and Nato's attacks on Libya.