An American salvage company has hauled up 43.5 tonnes of silver from the wreck of the SS Gairsoppa, a cargo ship sunk in the Second World War off the west coast of Ireland.

More than 1,200 silver bars, worth about $38 million under current market prices, were recovered from the Gairsoppa, a 126-metre, steel-hulled British merchant ship that was torpedoed by a German U-boat in February 1941, about 500 kilometres west of Galway.

A ladder leading to the forecastle deck of the SS Gairsoppa. One of the cargo holds can be seen at left. (Odyssey Marine Inc.)

In 2010, Odyssey Marine Exploration Inc. won a contract from the U.K. government to recover the Gairsoppa, which sat 4,700 metres deep in international waters in the North Atlantic, as well as another cargo ship, the SS Mantola, which was sunk in 1917 during the First World War.

As part of the contract, the company gets to keep 80 per cent of the net value of the silver bullion recovered. The U.K. government would not comment on the value of the contract but told BBC News last year that Odyssey Marine "offered the best rate of return" of the bids submitted.

Wreck holds 7 million ounces of silver

The Gairsoppa was owned by the British India Steamship Navigation Company and had been active in the commercial shipping industry since 1919, transporting valuable cargo through the waters of the Pacific and Indian Oceans.

In 1941, it was enlisted into service by the Ministry of War Transport, and was returning from Calcutta, India, when it and the convoy of merchant ships it was travelling in were attacked. Only one of the 85 people aboard survived.

Odyssey Marine crew members inspect silver bars as they are recovered from the SS Gairsoppa wreck and unloaded on the deck of the Seabed Worker on July 18. (Odyssey Marine Inc./Associated Press)

The ship was carrying about 6,350 tonnes of high-value cargo, including tea, pig iron and the silver bullions.

At the time of Gairsoppa's sinking, the U.K. Ministry of War Transport paid an insurance loss of approximately £325,000 (1941 value) to the private owners of the silver bars, Odyssey Marine said.

The company said there may also be uninsured silver aboard.

"Sources, including Lloyd’s Record of War Losses, indicate a cargo of silver worth £600,000 at the time, which would equate to approximately seven million total ounces of silver," the company wrote on its website.

As of Wednesday, the salvage crew had recovered about 1.4 million troy ounces (43,545 kg) of silver from the Gairsoppa, worth $38 million in today's prices, and the company hoped to haul up the rest within three months.

Odyssey Marine said the treasure salvaged so far was the heaviest and deepest recovery of precious metals from a shipwreck.

Found in 2011

To find the wreck of the Gairsoppa, Odyssey Marine chartered the Russian research vessel RV Yuzhmorgeologiya and employed deep-tow low-frequency sonar. It found the sunken ship in September 2011 and began the salvage operation in May 2012.

The company's recovery of Mantola, which was carrying approximately 600,000 ounces of government-insured silver when it went down, is also underway. It was found in October 2011 about 160 km from the Gairsoppa wreck off the southwest coast of Ireland.

The salvage operations are being filmed by JWM Productions, which will produce three one-hour television specials about the undertaking that will air on the Discovery Channel in the U.S. and Channel 5 in the U.K.