Image copyright AFP/DM PARODY Image caption Damage to HMS Ambush's conning tower could be seen as it arrived in Gibraltar on Tuesday evening

One of the UK's newest nuclear-powered submarines has docked in Gibraltar after a collision with a merchant vessel during a training exercise.

The Royal Navy said it has launched an immediate investigation after HMS Ambush was involved in the "glancing collision" while submerged off the coast of the British territory.

There is "some external damage" but no crew members were injured, it added.

The Astute-class attack submarine's nuclear reactor was undamaged.

In a statement on the Ministry of Defence website, the Navy said the incident took place at approximately 13:30 local time on Tuesday.

Further checks

"We are in contact with the merchant vessel and initial indications are that it has not sustained damage.

"The submarine suffered some external damage but there is absolutely no damage to her nuclear plant and no member of the ship's company was injured in the incident."

Further checks would be carried out but there are no safety concerns, said the Navy.

Photographs of Barrow-built HMS Ambush arriving in Gibraltar appear to show damage to the front section of its conning tower.

The submarine is reported to be a regular visitor to Gibraltar, having last stopped in the territory in June and March.

The Royal Navy's Astute-class submarines are Britain's largest and most advanced attack submarines - HMS Ambush is 97m (318ft) in length, cost £1.6bn and carries torpedoes and Tomahawk cruise missiles.

It joined the fleet at the Faslane naval base in 2013 after two years of sea trials.

Two other Astute-class submarines - Astute and Artful - are in service and four more vessels - Audacious, Anson, Agamemnon and the yet to be named seventh - are in various stages of construction.

The nuclear reactors of the Astute-class submarines will not need refuelling in their entire 25-year life and they make their own air and water, enabling them to circumnavigate the globe without needing to surface.

Astute grounding

In 2010, nuclear-powered submarine HMS Astute ran aground near the Isle of Skye during sea trails and was stuck for about 10 hours.

It was also damaged in a collision with a tug, the Anglian Prince, which tried to free it.

And there were protests in 2000 when the Royal Navy nuclear submarine HMS Tireless docked for repairs in Gibraltar after a crack was found in a cooling pipe near its nuclear reactor.

Residents in Gibraltar and southern Spain staged demonstrations over environmental concerns and the presence of the submarine became the subject of a high-profile campaign by Greenpeace.