The clandestine Russian operation, described by two Western officials, was carried out by Moscow's GUGI undersea warfare directorate, which used deep-sea submersibles.

The clandestine Russian operation, described to Reuters by two Western officials, was carried out by Moscow's GUGI undersea warfare directorate.

Britain and Norway disclosed in April that they had uncovered a covert Russian operation in Arctic waters. But the discovery of the new weapon and the location of the operation…