A survey of the sea bed 55 miles off the coast of Caister has unearthed an unexpected piece of history - a German U-boat from the First World War.
The wreckage was found when survey teams from energy companies Scottish Power Renewables and Vattenfall were working to draw up detailed plans for the new East Anglia ONE wind farm.
In a video posted online, it can be seen how the wreck has become a home for sea creatures and is now covered in barnacles.
At first, the team had thought they had discovered a Dutch military submarine which went missing in June 1940.
Andy Paine, Vattenfall project director of East Anglia Offshore Wind Farm said: 'We were all extremely keen to make contact with the Dutch Navy to see if this could be the submarine they have been looking for over so many years: could we at last have solved the mystery?'
But after studying German drawings, they have since confirmed the wreck is that of the German-built U-31.
Mark Dunkley, marine archaeologist at Historic England, said the U-31 was one of only two boats from its class which had not been found.
The sub left for routine patrol from Wilhelmshaven on the North coast of Germany on January 15, 1915, with more than 30 crew onboard. But it never returned.
'U-31 was the first of eleven type U-31 submarines built between 1912 and 1915,' Mr Dunkley said. 'The class were considered very good high sea boats with good surface steering. Eight were sunk during operations while three surrendered and were scrapped after the war. Of those lost during operations, the whereabouts and fate of two, including U-31, was unknown.'
It is believed to have hit a mine about 55 miles off Caister and is now on the sea bed in about 100 feet of water, where it will remain as an official military maritime grave.
Mr Dunkley added: 'After being on the seabed for over a century, the submarine appears to be in a remarkable condition with the conning tower present and the bows partially buried.'
There was a wartime rumour that the British had found the sub on the surface with the all the crew dead from gas poisoning, and that it was then towed to a British base, but this is now thought to be untrue.
Charlie Jordan, ScottishPower Renewables' project director for the windfarm said: 'The scanning team were expecting to see wrecks, but such a discovery was quite a surprise and has been extremely interesting.
'Unravelling the whole story behind the submarine has been fascinating and it's heartening to know that the discovery will provide closure to relatives and descendants of the submariners lost who may have always wondered what had happened to their loved ones.'
The wind farm developers have pledged to ensure that the remains are not disturbed when the new turbines are installed.
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