It’s been 80 years since a Dutch submarine vanished in the North Sea without a trace.
Now, the Dutch Navy is more determined than ever to find out what happened to the O-13.
Although part of the Netherlands defence, she joined allied forces in Scotland in May 1940 and was based in Dundee at HMS Ambrose.
She left the port in June 1940 with 34 crew on board, on her first and only mission.
The submarine was never to be seen or heard from again.
Joucke Spoelstra is a retired Naval officer for the Dutch Navy and is part of the team who have spent decades trying to find the vessel.
He said: “The O-13 was supposed to report home but she never did, so people thought at that moment that she was lost somewhere on a minefield.
“There are other theories of what happened to her of course, but since there was no German documentation of them destroying a submarine it was likely a mine.
“But we don’t know for sure what happened when she left the harbour, that’s still a mystery.”
The team is working alongside a range of specialists in a bid to locate the vessel using scans of the seabed and historical data to trace the submarine’s final movements.
The Navy believes the wreck may lie near to the Skagerrak, the Norwegian entrance to the Baltic Sea.
Now, 80 years since it’s disappeared, Joucke says it’s more likely the vessel will be found due to new technologies.
“People now have more drive to bring them back, because after the war the efforts were put into rebuilding towns and the military,” he said.
“They didn’t have the tools or the equipment that they have now.
“Saying that, it’s not that easy as there’s about 200 wrecks on the North Seabed from between 1914 and 1946.”
Amongst the lost crew was 35-year-old Sergeant Officer Willem Ausum who was a stoker on the O-13.
In his memory, one of his granddaughters is named after him.
Wil Verschoor is hopeful the vessel will eventually be found.
She said: “There were not a lot of stories about him, he was a strict man and very firm like my mum was.
“We don’t have any picture of him besides when he was in uniform, he was a proud man.
“It’s not so important where the boat is but what happened to it, I hope it was a mine so they didn’t know what hit them.”
The Dutch Navy plan to carry out further searches in the coming months.
Decades on, they hope the sea will finally give up the secret of what happened to the submarine and her crew.