Britain and France's nuclear submarines are so stealthy and their movements so secret that when a pair rammed into each other their crews had no idea what had happened, France said Tuesday.
"These submarines are undetectable, they make less noise than a shrimp," said Defense Minister Herve Morin when asked how such sophisticated vessels could have collided earlier this month amid the vastness of the North Atlantic.
The unprecedented accident has raised questions about whether the allies could have better coordinated their patrols, and whether France's imminent return to the NATO command structure might improve safety.
But defense officials said the movements of nuclear ballistic submarines -- which are designed to be undetectable -- are national secrets and that closer cooperation would be an extremely sensitive proposition.
Officials in the French naval staff, speaking on condition of anonymity, said that France already coordinates the patrol zones of its hunter killer subs with its allies, but that the nuclear missile fleet was separate.
Allied headquarters in Brussels houses officers and diplomats from dozens of countries and is considered prone to security leaks, making NATO members reluctant to share news about their most strategic ships.
"Nuclear deterrent is purely national, there are never exchanges on nuclear ballistic vessels," one French officer said.
NATO spokesman James Appathurai agreed. "NATO has no role in managing the movement of this class and type of submarine for any NATO nation," he said.
A Western diplomat attached to the Allied Headquarters in Brussels said that therefore France's membership or otherwise in the command structure had no bearing on the cause of the accident.
President Nicolas Sarkozy has already said that France's return to the NATO military command will have no bearing on its independent nuclear arsenal, and Morin insisted on the unprecedented nature of the accident.
So unusual, in fact, that at first the crews were not sure what happened.
"As soon as the incident occurred, the submarine's commander surfaced and said 'I have hit something. I think it was a container so I am heading back to Brest," Morin told French television.
"It's when we reported the incident that the British -- who had just learned from their commander that there had been a problem -- said: 'Well hey, we also had a problem'," he explained.
"The British came to inspect our submarine and they concluded that something happened between them."
Nevertheless, one NATO officer said that there would have to be an inquiry into the cause of the crash, insisting: "Just saying it was pure bad luck is not good enough."
Morin downplayed suggestions the subs may have been carrying out special maneuvers and rejected allegations the French navy had sought to hide the incident from the public until it surfaced Monday in the British press.
Both vessels involved in the crash -- Le Triomphant and HMS Vanguard -- are among the latest generation of Ship Submersible Ballistic Nuclear (SSBN) submarines and specifically designed to avoid being found.
While attack subs risk detection by sending out sonar pulses to detect enemy vessels, SSBNs lurk in the deep, running quietly, in order to be able to launch a surprise nuclear attack in the event of war.
France has maintained a sea-based nuclear deterrent force since 1971 and currently has three nuclear-armed submarines in operation. A fourth is undergoing sea trials and will come into service next year.
HMS Vanguard, launched in 1992, is one of four British nuclear submarines, one of which is always on deterrent patrol.
Both countries maintain that this month's accident did not compromise nuclear safety on board the vessels and had had no effect on the countries' nuclear counterstrike capability.© Wire reports