A collision between British and French nuclear submarines earlier this month in the middle of the Atlantic was a freak occurrence and the result of procedural deficiencies, maritime experts have said.
French officials said there were no injuries on board its vessel Le Triomphant
The incident, involving two nuclear-armed submarines, had never previously occurred and the odds of it happening again were next to zero, experts told news agencies this week.
"As far as I am aware, it is the first time that the submarines of two friendly nations have been involved in such an accident," said Stephen Saunders, the editor of online maritime and navy database Jane's Fighting Ships and a retired commodore told news agency AFP.
"No doubt there are a number of technical issues to be investigated, but the root of the problem appears to be procedural. These submarines should not have been in the same place at the same time.
"Even if two submarines do find themselves in the same area, it is still bad luck to have run into each other -- i.e. to be in the same place at the same depth."
Too much technology
Lee Willet, head of the maritime studies program at the Royal United Services Institute, a British defense and security think-tank, said hi-tech stealth equipment for submarines would have increased the likelihood of the collision.
"These are the strategic crown jewels of a nation. The whole purpose of a sea-based nuclear deterrent is to hide somewhere far out of sight and out of mind," he told AFP.
Conventional sonar technology may not have detected either sub, experts say
"Given that there are a very, very small number of SSBNs (Ship Submersible Ballistic Nuclear) in the world, the chances of two SSBNs being in the same bit of water at the same time is unprecedented.
"The fact that they couldn't hear each other is actually less surprising."
'Subs were hiding'
Saunders said that "the modus-operandi of most submarines, particularly ballistic-missile submarines, is to operate stealthily and to proceed undetected.
"This means operating passively (not transmitting on sonar) and making as little noise as possible.
"While in parallel 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."
Willett added: "Submarines don't go around advertising their position by pinging away with their sonar. It's very hard to hear stuff under water because of all the ambient noise.
"SSBNs listen passively using their sensing equipment but if you're listening for something that's making no noise, you can't hear it."
British defenses 'not diminished'
Britain says it still has a sufficient nuclear deterrent which will continue beyond 2020
The British vessel HMS Vanguard and the French U-boat Triomphant were both submerged and on separate missions in the mid-Atlantic at the time of the incident on February 4, news agency AFP quoted British press as having reported.
Both submarines were damaged in the incident but there was no reported damage to either the nuclear propulsion units or the nuclear-armed missiles the subs were carrying.
The Vanguard, which has a crew of 101, is one of four British V-class submarines armed with 16 ballistic missiles. Triomphant is also armed with 16 ballistic missiles with nuclear warheads and carries a crew of 125. The two submarines were on routine national patrols in the Atlantic Ocean at the time of the incident, the French Defense Ministry said in a statement.
The British Defense Ministry has refused to comment on the incident, other than to say that it had not diminished the country's nuclear defense capabilities. Both Britain and France have opened inquiries into the accident.