LONDON — A new British nuclear-powered submarine was towed free after running aground off the coast of northwest Scotland on Friday.

HMS Astute, the first of a new class of nuclear-powered submarines that was undergoing sea trials, became snagged on rocks off the Isle of Skye in an embarrassing incident for the Royal Navy.

The Navy had to wait for hours for high tide before tugs could tow the advanced submarine to deeper water.

"Two tugs attached lines to her and pulled her free at high tide," a Royal Navy spokesman said.

The submarine will be closely examined for any damage, he said.

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HMS Astute, commissioned into the Navy in August, is nuclear-powered but does not carry nuclear weapons. Britain's nuclear missiles are carried aboard four Vanguard-class submarines.

"This is not a nuclear incident," a Ministry of Defence spokesman said earlier. "There are no injuries to personnel and the submarine is watertight."

The submarine got stuck, for unknown reasons, during a routine exchange of crew members.

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"At some point she touched the rudder on the bottom and they weren't able to get her off immediately," a Navy spokesman said.

"There are no nuclear issues, no environmental impact, no injuries to people -- potential damage to the rudder, that's about it," the spokesman said.

The submarine's skipper, Cmdr. Andy Coles, chose not to force the vessel off the rocks, the U.K. Daily Telegraph reported, as that might have damaged the hull which the newspaper said was fitted with "some of the most advanced acoustic tiles that make Astute virtually undetectable beneath the seas."

David Moir  /  Reuters

People on a beach watch as crew work on the deck of the Royal Navy nuclear-powered submarine HMS Astute off the Isle of Skye,  Scotland on Friday.

The Telegraph said the $1.88 billion HMS Astute was the "world's most advanced nuclear submarine." Its nuclear reactor will not need refueling during the sub's life time in service.

The design, development and manufacture of the first three Astute-class submarines cost $6.1 billion.

Largest submarine
According to the Royal Navy's website it is the largest and most advanced sub the navy operates and will gradually replace the "Swiftsure" and "Trafalgar" classes.

Witness Ross McKerlich told BBC News when the submarine ran aground earlier: "She is now high and dry and we can see just the tips of her propeller.

"It looks as if it has developed a slight list. There was a helicopter hovering over the top and there are still just the two naval vessels from the local base.

"Earlier in the day, they did have ropes and they were trying to tow (the submarine)."

It's not the first time a British nuclear submarine has run aground off northwest Scotland.

In 2002 HMS Trafalgar got into trouble off the Isle of Skye during a military exercise and two crew were slightly injured. The surrounding coastline is used as a training ground by the Navy.

Britain's coalition government ordered cuts to Britain's armed forces this week to curb a record budget deficit. It confirmed it would go ahead with an order for seven new Astute-class submarines, built by BAE Systems.

The accident came the day after the U.K.'s Royal Navy celebrated Trafalgar Day, which commemorated the 205th anniversary of Admiral Horatio Nelson's famous victory over a combined French and Spanish fleet.