Spanish authorities are sending military planes to Florida for an important mission: to retrieve one of the richest shipwreck treasures in history.

Hulking Hercules transport planes will fly to Tampa, Fla. Monday or Tuesday to pick up 17 tons of treasure – worth $504 million – that had been tied up in US courts for years. 

US explorers found the treasure undersea in a Spanish galleon, the Nuestra Señora de las Mercedes, in 2007 off Portugal. Spain argued successfully in court that it never relinquished ownership of the ship or its contents.

The Civil Guard said agents would leave within hours to take possession of the booty, and two Spanish Hercules transport planes will bring it back. But it was not exactly clear when the planes and the agents would leave Spain.

Last week, a federal judge ordered Tampa-based Odyssey Marine Exploration to give Spanish officials access to the silver coins and other artifacts beginning Tuesday.

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The Spanish Culture Ministry said Monday the coins are classified as national heritage and as such must stay inside the country and will be displayed in one or more Spanish museums. It ruled out the idea of the treasure being sold to ease Spain's national debt.

Besides its debt woes, Spain is saddled with a nearly dormant economy and a 23 percent jobless rate.

Odyssey made an international splash in 2007 when it recovered the 594,000 coins and other artifacts from the Atlantic Ocean near the Straits of Gilbraltar. At the time, experts said the coins could be worth as much as $500 million to collectors, which would have made it the richest shipwreck treasure in history.

The company said in earnings statements that it has spent $2.6 million salvaging, transporting, storing and conserving the treasure.

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Odyssey fought Spain's claim to the treasure, arguing that the wreck was never positively identified as the Nuestra Senora de las Mercedes. And if it was that vessel, then the ship was on a commercial trade trip — not a sovereign mission — at the time it sank, meaning Spain would have no firm claim to the cargo, Odyssey argued. International treaties generally hold that warships sunk in battle are protected from treasure seekers.

The Nuestra Senora de las Mercedes was sunk by British warships in the Atlantic while sailing back from South America with more than 200 people on board.

Based on reporting by The Associated Press.

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