A NUCLEAR Royal Navy submarine has been forced into port in Gibraltar after a collision with a merchant vessel.

An immediate investigation has been launched after HMS Ambush was involved in the "glancing" collision while submerged off the coast of Gibraltar, the Royal Navy said.

The Astute-class vessel suffered "some external damage" but no crew members were injured in the incident.

The attack submarine's nuclear reactor was undamaged, the Royal Navy said.

A statement posted on the Ministry of Defence website said on Wednesday: "At approximately 1.30pm local time today, HMS Ambush, an Astute-class submarine, while submerged and conducting a training exercise was involved in a glancing collision with a merchant vessel off the coast of Gibraltar.

"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.

"An immediate investigation is being conducted.

"The submarine will be entering Gibraltar for further checks. There are no safety concerns associated with HMS Ambush being alongside."

The Astute-class are the largest, most advanced and most powerful attack submarines ever operated by the Royal Navy.

The boat was involved in the collision despite being equipped with what the Royal Navy boasts are "world leading sensors".

The 7,400 tonne Astute-class vessels, which cost more than £1 billion each, carry torpedoes for targeting enemy submarines and ships and Tomahawk cruise missiles.