An American company has made what is being called the heaviest and deepest recovery of precious metals from a shipwreck.

The Tampa, Fla.-based Odyssey Marine Exploration, Inc. announced Wednesday that it had recovered 48 tons of silver bullion from the SS Gairsoppa, a sunken British cargo ship in three miles of water off the coast of Ireland. Between the Gairsoppa, torpedoed by a German U-boat during World War II, and the SS Mantola, sunk by a German submarine during World War I, Odyssey said in a press release that about 240 tons of silver may be recovered by the end of the operation.

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The recovery is being made under a contract awarded by the U.K. government, which will keep 20 percent of the cargo's value, estimated to be in the tens of millions of dollars. The Gairsoppa became U.K. property after the government paid the owners of the ship an insurance sum of £325,000 in 1941. Records indicate the silver was valued at £600,000 in 1941.

The initial recovery of 48 tons consists of 1,203 silver bars and has been transported to a secure facility in the United Kingdom, according to the company.

"With the shipwreck lying approximately three miles below the surface of the North Atlantic, this was a complex operation," Odyssey CEO Greg Stemm said in Odyssey's release.

Odyssey contracted JBR Recovery Ltd., a European silver recovery and precious metal processing company, to assist in refining and monetizing the recovered silver.

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The Gairsoppa and Mantola shipwrecks were discovered in 2011, and Odyssey conducted reconnaissance dives at both sites in March and April 2012. Recovery operations began in late May.