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 3 and 4 February 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, according to The Independent, the Ministry of Defence was forced to confirm the embarrassing collision between strategic allies 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.
Defence sources said the accident was the result of the "infinitesimal" coincidence that both submarines were operating at the same depth and location in the Atlantic.
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 and the height of a three-storey building could be explained by the development of stealth technology, making the submarines less visible to other vessels.
Anti-nuclear campaigners said the two vessels had been moments from a potentially catastrophic accident, which could have resulted in the widespread release of radioactive material.