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LONDON - Defence chiefs are facing an inquiry into the safety of Britain's nuclear deterrent after British and French submarines, each laden with missiles powerful enough for 1248 Hiroshima bombings, collided while submerged in the mid-Atlantic.
HMS Vanguard, the lead boat of Britain's fleet of four V-class submarines armed with Trident nuclear missiles, limped back into its home port of Faslane in Scotland on Saturday showing significant damage. Witnesses said the hull was scarred with dents and scrapes.
The weather was rough in the middle of the night of February 3 and 4 when the British submarine, which was carrying 135 crew, struck Le Triomphant, the flagship of the French nuclear strike force, destroying the French vessel's fibreglass sonar dome, which juts out from the bow and, among other tasks, is supposed to detect other submarines.
In London, the Ministry of Defence (MoD) tried to maintain its policy of secrecy about the movements of Britain's nuclear fleet, but it was forced to confirm the collision after the French Navy posted details of the accident on its website.
Both countries insisted that neither the missile-launching capacity nor the nuclear safety of the submarines, carrying 265 crew and 32 intercontinental ballistic missiles, were affected.
Admiral Sir Jonathon Band, the First Sea Lord, said: "Recently, the two submarines came into contact at very low speed. Both submarines remained safe and no injuries occurred. We can confirm that the capability remained unaffected and there has been no compromise to nuclear safety."
Defence sources said the accident was the result of the "infinitesimal" coincidence that both submarines were operating at the same depth and location.
Nato allies routinely share information about the deployment of submarines to ensure they do not occupy the same area of ocean, an arrangement in which the French, whose nuclear deterrent remains independent, are understood to participate.
Stephen Saunders, a retired British Royal Navy commodore and the editor of Jane's Fighting Ships, said that neither submarine would have had a precise position for the other.
"The whole point is to go and hide in a big chunk of ocean and not be found. They tend to go around very slowly and not make much noise," Saunders said.
Politicians said the incident raised serious questions about the precautions to protect the V-class nuclear vessels, which, at nearly 16,000 tonnes and 150m long, are among the largest submarines ever built.
Similar questions were being asked in France, where the 14,335-tonne Triomphant returned to its base at L'Ile Longue, near Brest. The boat will spend up to four months undergoing repair. The French Navy initially claimed the submarine had been in a collision "apparently with a container".
Angus Robertson, the leader of the Scottish National Party in Westminster, said: "The MoD needs to explain how it is possible for a submarine carrying weapons of mass destruction to collide with another submarine carrying weapons of mass destruction in the middle of the world's second-largest ocean."
Naval experts, who underlined that the two nuclear submarines were built with hulls designed to withstand huge pressures, expressed surprise that the sonar arrays of both had failed to detect either vessel.
Sonar technology is now so sophisticated manufacturers boast it can recognise a small fish.
That it does not seem to have been able to pick out a submarine nearly the length of two football pitches could be explained by the development of stealth technology, making the submarines less visible to other vessels.
Stephen Saunders said: "The modus operandi of most submarines, particularly ballistic-missile submarines, is to operate stealthily and to proceed undetected. This means operating passively, by not transmitting on sonar, and making as little noise as
possible. A great deal of technical effort has gone into making submarines quiet by reduction of machinery noise. And much effort has gone into improving the capability of sonars to detect other submarines; detection was clearly made too late or not at all in this case."
Several serious accidents have befallen the UK's submarine fleet. In 2002, HMS Trafalgar suffered damage when it ran aground on rocks off Skye in training.
Last week, an inquest heard how two sailors on the Trafalgar's sister vessel, HMS Tireless, died in an explosion caused by a faulty oxygen generator.
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