Seventy years ago, the British merchant ship the SS Port Nicholson was sunk by U Boats off the coast of Cape Cod. According to the British Government its cargo amounted to little more than machinery and military stores bound for allies in the United States.
But an American treasure hunter believes the official story masks a spectacularly more lucrative reality.
Adventurer Greg Brooks of Sub Sea Research yesterday claimed to have located 30 boxes of platinum bars within the ship's hold, worth up to $3bn (£1.9bn). "I'm going to get it, one way or another, even if I have to lift the ship out of the water," he said.
If substantiated, the hoard – also said to include gold bullion and diamonds – would be the richest haul of sunken treasure ever discovered. It also promises to kick off a bitterly contested international maritime dispute.
Mr Brooks claims the ship was part of a convoy bringing Soviet payment for continued US support in the war against Hitler.
Having discovered the ship in 2008, 50 miles off-shore in 800ft feet of water, the Maine-based company obtained salvage rights from the US courts.
But the British Government has hired a lawyer to monitor the situation and to potentially challenge any future moves towards ownership.
US attorney Anthony Shusta said: "We're still researching what was on the vessel. Our initial research indicated it was mostly machinery and military stores."
Yet there remains the not inconsiderable task of bringing the platinum to the surface.
A British and a US company have both previously probed the wreck and are believed to have recovered some treasure, while Atlantic conditions make sustained work challenging.
To further compound matters, Sub Sea Research needs money to continue its search and is in talks with potential backers to upgrade equipment.
The company claims to have verified the identity of the vessel by its hull number using a remote underwater camera. Researchers have tracked down survivors of the convoy, and ledgers which confirm the nature of the secret cargo then worth $53m (£33.5).
A Department for Transport spokesperson said: "Under the War Risk Insurance scheme, merchant vessels lost during the two world wars became the property of the UK Government if insurance was paid out. The UK is therefore the owner of the wreck of the SS Port Nicholson. To protect our interest in the vessel, and its contents, we are currently party to court proceedings in the US and are considering our next steps."
The SS Port Nicholson was in an armed convoy between Halifax, Nova Scotia and New York when it was holed by two torpedoes killing two seamen while more than 80 crew members were rescued. Five more sailors died, including the ship's master, as they returned to inspect the stricken steamer hours later. Another vessel, the troop ship Cherokee, was also sunk in the attack with the loss of 89 men.