How Stealthy Are Nuclear Submarines?

In the end, it was only an underwater fender bender, but a low-speed crash in February 2009 involving Britain's HMS Vanguard and France's Le Triomphant could have been catastrophic. At the time of the collision, the two nuclear-powered submarines were patrolling the deep waters of the North Atlantic off the coast of France. Despite state-of-the-art sonar capabilities, neither submarine was able to detect the other -- probably because neither was operating its active sonar at the time.

When on patrol, submarines operate in stealth mode; turning on active sonar automatically reveals a boat's location. The hulls of both submarines – each carrying nuclear weapons -- were covered with anechoic tile to reduce sonar detection, and the boats' passive sonar would not have detected the presence of another nearby sub.

Nuclear deterrents under the sea:

• Each submarine was armed with 16 nuclear missiles -- enough destructive power to equal 1,248 Hiroshima bombings. The collision damaged both vessels but no radioactive material was released.
• Submarines are key elements in the nuclear deterrent policies of both Britain and France. Lack of communication between France and other NATO members is also believed to have contributed to the crash.
• The Campaign for Nuclear Disarmament described the incident as "a nuclear ­nightmare of the highest order.” Britain has continuously deployed at least one nuclear-armed submarine in the Atlantic since the 1960s.