A nuclear-powered submarine ran aground off the coast of the Isle of Skye today, the Ministry of Defence confirmed.
There were no reports of any injuries in the incident involving HMS Astute.
A Ministry of Defence spokesman said: "We are aware of an incident involving one of our submarines off the Isle of Skye. This is a not a nuclear incident.
"We are responding to the incident and can confirm that there are no injuries to personnel and the submarine remains watertight. There is no indication of any environmental impact."
It was understood that the submarine's crew were waiting for high tide so they could free the vessel.
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A taxi driver with Skye Car Hire said: "From the angle I could see it, it looked like it was grounded out to the lighthouse.
"It looks like it has run ashore in shallow water by Eilean Ban, the wee island that the bridge goes across. You can see it very well from the bridge."
In June 2007 the mammoth 3.5 billion nuclear-powered HMS Astute was named and launched by the Duchess of Cornwall.
The submarine weighs 7,800 tonnes, equivalent to nearly 1,000 double-decker buses, and is almost 100 metres (328ft) long.
Its Spearfish torpedoes and Tomahawk cruise missiles are capable of delivering pin-point strikes from 2,000km (1,240 miles) with conventional weapons.
The submarine's nuclear reactor means that it will not need refuelling once in its entire 25-year life and it makes its own air and water, enabling it to circumnavigate the globe without needing to surface.
• This photo shows the HMS Astute grounded in shallow waters off the coast of Skye today
A spokesman for the Maritime and Coastguard Agency said: "We have sent a coastguard tug to where the submarine ran aground on rocks at the Kyle of Lochalsh near the Skye bridge.
"It will stand by and monitor what will be going on. We think on the rising tide, at around 6pm, there should be some movement of the vessel."
Nigel Smith, who runs glass-bottom boat trips in the nearby Kyle of Lochalsh, said the submarine had been stuck for hours.
He said: "It's very close inshore and the tide is still falling, so it's going to be high and dry.
"It's not far from the Skye Bridge and there are people now lining the streets to try and get a look.
"They tried to tow it off but that has been unsuccessful. They might be able to get away at high tide but that's not for a while.
"I can't imagine what happened, maybe a navigational error or a systems error but it's unusual to see. I imagine the commander will be baffled at the moment as to what has happened."