HMS Astute has been at the centre of a series of bad news stories
The hi-tech stealth vessel was taken to the Faslane Naval Base on the Clyde late on Friday when it suffered “a technical issue with hydraulics”, according to a Ministry of Defence (MoD) source.
“This needs to be fixed to make sure it can dive properly,” the source said. “It could take days, or it could take weeks.”
Experts say that the boat’s hydroplanes, which enable it to dive or surface, are hydraulically controlled. If they fail, the boat could be lost, along with its entire crew of 98.
The ill-fated HMS Astute is infamous for being the scene of a fatal shooting a month ago when it was docked in Southampton, and for accidentally running aground off the Isle of Skye last October. The boat has been plagued by a series of other mishaps, including a fire, being hit by a falling ramp and problems with its toilets.
HMS Astute left Faslane on Wednesday for sea trials, but returned soon after just two days. One insider told the Sunday Herald that the captain, Commander Iain Breckenridge, had “no confidence in the performance of the vessel”.
The nuclear consultant, John Large, who has advised governments on submarine safety, pointed out that the hydraulics that controlled the hydroplanes were “a fundamental safety system that can’t be ignored”.
He said: “If you don’t have the hydraulics, the boat could sink with all hands on board. It’s a serious problem.”
The danger that submarines like HMS Astute could have difficulties surfacing was highlighted in a secret report by the MoD’s own nuclear safety watchdog. Commodore Andrew McFarlane, the chief defence nuclear safety regulator, warned that there was a “risk of multiple fatalities resulting from loss of depth control”.
His report was released under freedom of information law with large sections blacked out.
But researchers discovered that the censored text could be read simply by cutting and pasting it into a new document.
This revealed that British submariners were more likely to drown than their American counterparts if the reactor that powered their boat failed while they are under water. British submarines “accept a much lower reliability from the main propulsion system” and the back-up system “will not provide sufficient dynamic lift”, McFarlane said.
HMS Astute is the first of seven “state-of-the-art” Astute class submarines, which are being built at Barrow in Cumbria. They have been beset by delays and budget overruns, and could end up costing over £10bn.
The Royal Navy operates 10 other nuclear-powered submarines out of Faslane, including four Vanguard class boats, which carry Trident nuclear missiles. The Sunday Herald disclosed in April that one of them, HMS Vengeance, had to cut short a training exercise in the North Atlantic when its propeller became blocked with debris.
An MoD spokeswoman said: “We do not routinely comment on submarine movements.”