The Ministry of Defence (MoD) has confirmed that HMS Vigilant, a nuclear-powered submarine capable of carrying nuclear warheads, was disabled while on the way home to the Faslane naval base on the Clyde after test-firing a Trident missile in the Atlantic off the coast of Florida on October 23.
The submarine is understood to have turned around and returned to the US naval base at Kings Bay in Georgia, near Florida, where the damage is now being investigated and repaired. The base is home to the US fleet of Trident submarines.
A submariner on Vigilant revealed that the boat's planned schedule had been disrupted when he complained on Twitter that he was "stuck in the USA for Christmas". Vigilant was due to return to Scotland to recommence continuous patrols of the oceans after a three-year overhaul.
The MoD has released few details of what happened because the operations of Trident submarines have the highest security classification. The ministry never usually says where the boats are, or whether they are carrying nuclear weapons.
"While returning to the UK after the successful firing of an unarmed Trident II D5 missile, HMS Vigilant suffered a defect to her rudder," an MoD spokesman said. "This is not nuclear-related and the crew and boat have safely returned to port where the defect is being assessed."
A source told the Sunday Herald that damage had been caused by "debris at sea", but this was not confirmed by the MoD. "There is no evidence that there was a collision at sea," said the MoD spokesman.
Steven Savage, a sailor currently serving on Vigilant, sent a tweet on December 8 to the BBC in Teesside saying he was missing Middlesbrough Football Club, known as Boro.
"Can we have a shout out to all the Boro fans on HMS Vigilant (submarine). Stuck in the USA for Xmas #missingtheboro," he said.
Vigilant is one of four Vanguard-class submarines equipped to carry nuclear-tipped Trident missiles. One submarine is meant to be patrolling the seas 24/7 as part of a policy of "continuous at-sea deterrence".
Last month, Defence Minister Philip Dunne told Parliament that Vigilant had recently completed a major overhaul.
Test-firing the missile was part of a "demonstration and shakedown operation" designed to demonstrate the effectiveness of the UK's nuclear deterrent before the submarine returned to service.
According to the Royal Navy, the overhaul cost more than £300m, took three years and involved refuelling the submarine's reactor. More that 200 significant upgrades were made to the submarine's machinery and operating systems.
Critics questioned how a submarine that had just undergone such an extensive and expensive overhaul could immediately break its rudder. They were also concerned about whether it would be safe to sail with a defective rudder.
"The navy is probably very concerned about this," said John Large, an independent expert on nuclear submarines. "It may be that the maintenance work caused the problem."
He suggested that the rudder could have suffered a mechanical failure with its hydraulics or communications systems, or may have snagged on a cable used to tow a sonar array to detect other submarines.
The incident would also have been embarrassing, Large argued. "I would imagine the boat would have to surface, which is a disaster for a stealth submarine because it can be seen," he said.
He also pointed out that Trident submarines were very dependent on keeping to their programme. "If something goes wrong it completely screws up the schedule," he added.
John Ainslie, co-ordinator of the Scottish Campaign for Nuclear Disarmament, claimed that sailing a Trident submarine across the Atlantic with a "dodgy" rudder could cause a collision with "catastrophic consequences".
He also claimed that repairs would delay when Vigilant becomes fully operational. "It will have an impact on the navy's ability to keep one Trident submarine at sea at all times," he said.
"Rather than rushing to patch up the rudder, the MoD should follow the Liberal Democrats' advice and end continuous at-sea deterrence. Then they can take as long as they like to fix this problem."
Another Trident submarine, HMS Vanguard, famously collided with a nuclear-armed French submarine, Le Triomphant, in February 2009 somewhere in the Atlantic. Both boats had to return home for repairs.