The collision between French and British nuclear submarines in the middle of the Atlantic is "more embarrassing than worrying", a naval expert said today.
Former Royal Navy officer Mike Critchley suggested the accident appeared to have happened because the vessels' anti-sonar technology was "too good".
But the Campaign for Nuclear Disarmament (CND) voiced grave fears about the possible outcome of the incident, describing it as "a nuclear nightmare of the highest order".
The submarines, HMS Vanguard and French vessel Le Triomphant, were both damaged when they collided at low speed earlier this month.
HMS Vanguard, which came into service in 1993, is one of the four submarines that make up Britain's nuclear deterrent.
It carries up to 16 Trident nuclear missiles, with a maximum of 48 warheads.
Mr Critchley stressed that the submarines had massively reinforced hulls and were designed to take "an incredible amount of punishment".
He said: "If and when these accidents do happen, you're prepared for them.
"The real reason for building them with steel so thick is the pressure the water puts on them at depth. They can take the punishment."
Mr Critchley, publisher of Warship World magazine, based in Liskeard, Cornwall, said the collision was a "one-in-a-million chance".
It raises questions about whether the Navy should share more detailed information about the movements of its ships with its Nato allies, he added.
"These vessels are designed to go into the oceans' depths and not be found," he said.
"We are not talking about a small German U-boat here, we're talking a huge vessel the size of a block of flats - but they do have a lot of stealth technology on board."
This is not the first serious incident in recent years involving Royal Navy submarines.
In March 2007 two British sailors were killed in an explosion on board HMS Tireless during a war games exercise beneath the Arctic icecap.
In May 2003 HMS Tireless crashed into an object, possibly an iceberg, while on patrol in the Arctic.
And in November 2002 HMS Trafalgar suffered considerable external damage after running aground on rocks three miles off the Isle of Skye while taking part in a two-week training exercise.
Mr Critchley suggested budget cuts may have left some Navy officers without enough practical experience.
"Once you get out into the ocean deep, you are moving in three dimensions," he said.
"The training is extensive, but whether the people who are in command of these major assets have considerable experience at sea is questionable because the Navy has been seriously cut back in recent years.
"So the progression from a junior officer to a senior officer includes far more shore time than sea time.
"So that is why, I would suggest, some accidents have happened in the past. The Navy employs human beings and human beings make mistakes."
The worst submarine disaster of recent years was the death of 118 sailors aboard the Russian vessel Kursk after it crashed to the bottom of the Barents Sea in August 2000.
CND chair Kate Hudson alleged that the French and British submarines that collided were "no more than a couple of seconds away from total catastrophe".
She added: "This is the most severe incident involving a nuclear submarine since the sinking of the Kursk in 2000 and the first time since the Cold War that two nuclear-armed subs are known to have collided.
"These dangers are inherent whilst the British Government maintains its 1960s policy of having at least one nuclear-weapons submarine sailing round the Atlantic 24 hours a day, 365 days a year."Reuse content