A nuclear-powered submarine which had run aground off the Isle of Skye was damaged in a collision with a tug which tried to free it, it has emerged.
HMS Astute was towed free on 22 October after becoming stuck on a shingle bank for about 10 hours.
The Navy has confirmed a collision between the £1bn vessel and a Coastguard tug caused damage to the submarine's starboard foreplane.
The extent of the repairs now required is being investigated, the MoD said.
HMS Astute, the Royal Navy's newest sub, was on sea trials when it became stuck. It was freed when the tide began to rise.
It is understood that the Coastguard tug involved in the collision was the Anglian Prince.
In a statement, the MoD said: "We can confirm that one of the towing vessels came into contact with HMS Astute.
"The area of the collision was inspected at the time and she was able to proceed.
"Further investigations are under way to determine the extent of the repairs required as a result of the grounding and the collision."
A Navy spokesman said the damage to Astute would be repaired at its Faslane base and the vessel's trials would resume in due course.
A spokesman for the Maritime and Coastguard Agency said it was investigating the collision.
HMS Astute, which was built by BAE Systems in Barrow in Furness, Cumbria, is not expected to formally enter service until next year.
It can carry a mix of up to 38 Spearfish heavyweight torpedoes and Tomahawk Land Attack cruise missiles.