Discovery of buried silver treasure on the SS Gairsoppa. It is the heaviest and deepest recovery of precious metals from a shipwreck. (Odyssey Marine Exploration)
Silver on the SS Gairsoppa. It is the heaviest, deepest recovery of precious metals from a shipwreck (Odyssey Marine Exploration)

Explorers have uncovered a silver treasure haul worth £20m in a British merchant ship sunk by a Nazi U-boat in 1941.

The lost treasure, which was found in two separate dives in 2012 and 2013, consists of 2,972 ingots of .999 silver, the purest and most valuable form of the metal.

The haul includes 462 bars of pure silver, which are engraved with the mark of 'His Majesty's Mint Bombay'

It's hailed as "the largest known precious metal cargo ever recovered from the sea", by the Odyssey Marine Exploration company which located the haul.

The 2,972 silver bars were hauled from the SS Gairsoppa and are now in Bristol.

The ship was sunk around 300 miles southwest of the Irish coast, in British waters.

When the silver goes on sale, the British Treasury will receive a 20% cut.

Odyssey Marine Exploration, a US marine archaeology company that discovered the shipwreck and paid for all the recovery costs, will take the remaining 80% of the net proceeds.

The Gairsoppa was carrying 7m ounces of silver when the ship broke away from a protective convoy and made for Galway Harbour.

Unprotected and alone in the Atlantic, the Gairsoppa was spotted by a German plane, and then torpedoed by a U-boat.

The British merchant ship took just 20 minutes to sink, with most of the mainly Indian crew of 85 losing their lives.

A handful of men managed to make their way to Cornwall in a lifeboat, but only Richard Ayres, the second officer, survived the journey.

Odyssey's principal marine archaeologist Neil Cunningham Dobson says: "Even though records indicate that the lifeboats were launched before the ship sank, sadly most of her crew did not survive the long journey to shore. By finding this shipwreck, and telling the story of its loss, we pay tribute to the brave merchant sailors who lost their lives."

The ship lay undiscovered on the ocean bed, at a depth of four miles, for 70 years. It was identified by Odyssey Marine Exploration in 2011.

Using remote controlled equipment, the hull of the Gairsoppa was carved open to reveal 1,200 bars. The ingots each weigh 80lb, are the shape of a loaf, and engraved with the words "His Majesty's Mint Bombay".

The Odyssey Marine Exploration company is also hoping to explore the wreck of the HMS Victory this year. The ship was the forerunner to Lord Nelson's flagship at the battle of Trafalgar.

The HMS Victory sank in a storm off Guernsey in 1744. It lies at a depth of 320 ft, and carries around 100 cannons.

"After Mary Rose [Henry VIII's flagship], it is the most important of the historic shipwrecks," Sean Kingsley, a marine archaeologist told the Times.

"What's really significant is that this is an extremely rare example of an early Georgian Warship."

Watch underwater views of the shipwreck of SS Gairsoppa

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