While en route to the Caribbean, the Portsmouth-based patrol vessel HMS Medway transported the loggerhead turtles to the Azores before releasing them.

The juvenile turtles had been swept from the Caribbean or Eastern Seaboard of the US by strong winds and Atlantic currents towards the UK, before being found and rescued.

They were rehabilitated by Newquay's Blue Reef Aquarium and Anglesey Sea Zoo, having been "cold stunned" by the cold waters around the UK.

It is believed they would have died if they had not been found.

Two of the turtles, named Jason and Perran, were found at Perranporth, Cornwall; Gordon was discovered at Bude in Cornwall; Hayle was found in Hayle, Cornwall; Holly on Putsborough Beach, Devon; and Tonni was rescued at Moel-y-Don beach, Anglesey.

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Steve Matchett, group curator for Blue Reef Aquarium, said: "All the turtles arrived in a weakened state - in many cases we were unsure if they were going to make it overnight.

"All were dehydrated and emaciated. This is due to being too cold for a long period and being unable to feed or function properly. They have all prospered once we got them past the initial stages.

"We are very grateful to the navy for stepping in to repatriate these rescued turtles."

The six turtles were dropped into the Atlantic off the Azores, watched by the ship's crew which had gathered on the flight deck to watch.

Rod Jones, the Royal Navy's senior maritime environmental protection adviser, said: "As professional mariners, many of us are keen to do what we can to reduce the loss of biodiversity at sea.

"Encountering marine wildlife is one of the great joys of seafaring and if we can assist, even in a small way, to make that more likely in the future we are pleased to be able to do that.

"Assisting turtles to return to warmer waters may not be the Royal Navy's primary role but as a government body we are very pleased to be able to support the UK's ambition for more healthy and diverse seas."

Frankie Hobro, owner of Anglesey Sea Zoo which cared for Tonni - which is Welsh for wave - since the turtle was washed up next to the aquarium 20 months ago, said: "In one way there's going to be this little bit of you swimming off into the Atlantic.

"In another, this is what we have been aiming for since day one. We're excited and a little bit emotional in a happy way."

Medway sailed from Plymouth last week to relieve its sister ship HMS Trent, supporting international counter-drug smuggling operations across the Americas, and assisting island communities should they be hit by storms during the hurricane season.