Deep in Arctic waters near the remote Svalbard archipelago this spring, NATO allies caught Russian submarines training to unleash a secret weapon designed to disable critical undersea cables without leaving any fingerprints.The clandestine Russian operation, described by two Western officials, was carried out by Moscow's GUGI undersea warfare directorate, which used deep-sea submersibles to simulate the deployment of the sophisticated technology.A joint operation involving Britain, Norway and the US tracked and confronted the Russian vessels at sea, said the two officials speaking on condition of anonymity. The vessels were prevented from completing their exercise and eventually left the area.Britain and Norway disclosed in April they had uncovered a covert Russian operation in Arctic waters. But the discovery of the new weapon, the location of the operation and the US involvement have not been reported.The deep-sea face-off comes at a time when some Western intelligence officials fear the Kremlin is ramping up sabotage operations in Europe and preparing for a conflict with NATO.US intelligence analysts are increasingly concerned Russia may test NATO's mutual defence pact, known as Article 5. If it does, destroying subsea cables could be a critical part of that effort, the Western officials said.Cables no thicker than a garden hose, lying on the seabed or buried just below, are critical to global internet connectivity and financial transactions. Surface and sub-surface satellite imagery of Russia's Main Directorate for Deep Sea Research (GUGI) associated vessels based at Olenya Guba in Russia President Vladimir Putin gestures during a Russian-Vietnamese meeting at the Kremlin