The Ministry of Defence could face a bill of hundreds of millions of pounds to repair a nuclear-powered submarine which ran aground last week, depending on the damage, an expert tells Channel 4 News.
The incident, in which the HMS Astute ran aground near the Isle of Skye, could also have longer term implications for the viability of the rest of the Astute-class fleet if any generic weakness in the boat is uncovered, Channel 4 News understands.
The HMS Astute ran aground on Friday during a sea trial. It has been transported into shore and the extent of the damage will be assessed by the Royal Navy at the Faslane base over the next couple of days. It remains unclear how the incident happened.
The Ministry of Defence has already confirmed that the boat is watertight and the nuclear system on board has not been damaged. But there could be damage to other parts of the ship - including its propulsor or external sonar system - and kinks or dents to the hull.
Submarine expert John Large, a nuclear engineer who led the risk assessment team for the raising of the damaged Russian nuclear submarine Kursk, told Channel 4 News the cost of the repair was likely to be millions.
Depending on the damage, repairs to the £3.5bn submarine could cost between £1-2m right up to more than £100m, he said.
"It is inevitable there will be some damage," he said. "It's very difficult to know what exactly until the Navy has done its full assessment.
I'd say some kind of damage is almost guaranteed. John Large, nuclear submarine expert.
"But if the propulsor has been damaged, that can be repaired, and would cost between £1-2m. It would be local patchwork, and would come into dock and be repaired at Devonport. But if the hull has been damaged, that could be very significant," he added.
The 7,800 tonne submarine has a lot of sensitive equipment along its hull in various places, he said, so the costs would depend on where the damage was, if any was caused when the boat ran aground.
"If the hull is kinked or buckled at the front, that's not so much of a problem. But if is damaged at the back - where the engine room is - the repair process will have to see all the equipment taken out. To give you an idea, to get the torpedoes into the older class of submarines, half of the submarine had to be dismantled.
"So that could cost tens to hundreds of millions, right up to being scrapped if the damage is serious. But that's unlikely as if there had been serious damage it would have gone to its emergency berth," he added.
The submarine has equipment on its underbelly including sonar panels, Mr Large said, which could also have been damaged.
"I'd say some kind of damage is almost guaranteed," he said. "At the back end, there's the propulsor, on the underbelly there's probably some damage to the sonar panels, and the decoy tubes. The Navy has broken one of its most expensive toys."
Mr Large said that a major concern for the Royal Navy would be whether, if the hull had been damaged or buckled in any way, this indicated a systemic weakness within the Astute-class fleet. Britain plans to buy a total of seven submarines of this type, despite cuts to the defence budget, and is already at an advanced stage with two other vessels.
The HMS Astute was launched in 2007 by the Duchess of Cornwall and the grounding occurred during a sea trial.
Mr Large said: "If this shows a generic weakness in the hull, then successive Astutes will have to be modified, and that would be very expensive," he said. "And if there's some delay - if it takes six months or a year to repair the HMS Astute - there will be a shortfall in the fleet of hunter killers as others are decommissioned. So that's basically a shortfall in the defence of the realm.
"It's really a very embarrassing, possibly quite serious, incident," he said.
Ministry of Defence investigation
A Ministry of Defence spokesman said: "The HMS Astute is back at Faslane today. There was an initial assessment and it is seaworthy, but it has gone back for further checks."
He said the extent, and cost, of any damage had not yet been determined and would be assessed in more detail.
A Royal Navy investigation into how the incident happened has also been launched. Channel 4 News understands the commanding officer of the HMS Astute, Commander Andy Coles, could face a court martial.