Nuclear submarine collision a 'very serious incident'

However much the Ministry of Defence was trying to play it down – or, indeed, avoid saying anything until news of it was leaked to the press – the significance of the collision between British and French nuclear missile submarines in the middle of the Atlantic must not be underestimated, say independent analysts.

"Friendly submarines should not bump into each other. Unquestionably, it is a very serious incident," said Commodore Stephen Saunders, a former senior Royal Navy officer, now editor of Jane's Fighting Ships.

Submarines, especially those carrying ballistic missiles with nuclear warheads, are not supposed to be heard. Equipped with modern passive sonar, they should not be detected. However, the sonar and radar are supposed not only to try to find out what other submarines are about but also to avoid collisions.

Large submarines such as Le Triomphant and HMS Vanguard are not very manoeuvrable, and analysts described the accident as extremely bad luck.

Yet the incident raises other questions that the inquiry being conducted by the French and British navies will also have to answer. Nato navies work together to "deconflict", as Saunders put it, to ensure their boats, even those on sensitive, secretive missions are not in the same area at the same time.

Though Nicolas Sarkozy wants France to rejoin Nato's integrated military structure – an announcement that France is breaking with its Gaullist past is expected at the Nato 60th anniversary summit in Strasbourg in April – it is not there yet. Even so, it is surprising that French navy liaison officers did not tell their British counterparts of its submarine's whereabouts, and vice versa, say analysts.