TAMPA, Fla. — Leaving nothing to chance, the U.S. military is making sure the transfer of 17 tons of shipwreck treasure to Spain later this week is handled safely.

Officials at Tampa’s MacDill Air Force Base said Tuesday night that they are cooperating with the Spanish government on the transfer of the of 594,000 coins and other artifacts that were wrested away from deep-sea explorers Odyssey Marine Exploration after a nearly five-year legal struggle.

The company salvaged the treasure and flew it back to Tampa via Gibraltar in May 2007. At the time, it was estimated to be worth around $500 million to collectors, which would have made it the richest shipwreck in history.

The treasure is believed to be from the Nuestra Senora de las Mercedes, a galleon with more than 200 people on board that was sunk in 1804 by British warships in the Atlantic Ocean while sailing back from South America.

Spanish experts are working under a veil of secrecy as they prepare to move the treasure later this week on two C-130 military transport sent to the U.S. for the purpose. Citing security concerns, no one is talking about the timing of moving the coins, but James Goold, a Washington attorney who represented the Spanish government told a federal judge last week the items would be trucked out of the secure facility where they’ve been stored and on their way to Spain by Friday.

“The U.S. Air Force has an excellent relationship with the Spanish Air Force and we are working closely with them to ensure a safe and secure mission,” said the brief statement from base Tuesday night, which included few details.

Odyssey officials agreed in court last week to give the Spanish government access and said the company would not oppose the efforts.

Experts were inspecting and inventorying the coins and artifacts and were on track to meet the timeline he cited in court, Goold said Tuesday.

“We’re on schedule,” he said.

The exact storage location also hasn’t been disclosed, but handling and conservation of the coins was performed by Sarasota, Fla.-based Numismatic Guaranty Corp.

The company spent $2.6 million salvaging, transporting, storing and conserving the treasure, according to earnings statements. But it is not expected to receive any compensation from the Spanish government for recovering the treasure because the European nation has maintained that the company should not have tried to do so in the first place. Goold has likened the salvage of shipwrecks for profit to plundering for souvenirs the wreck of the USS Arizona in Pearl Harbor, Hawaii.

Odyssey, which uses remote-controlled vehicles to explore the depths and bring the tiniest of items to the surface, argued that as the finder it was entitled to all or most of the treasure. The Spanish government filed a claim in U.S. District Court soon after the coins were flown back to Tampa, saying it never relinquished ownership of the ship or its contents. A federal district court first ruled in 2009 that the U.S. courts didn’t have jurisdiction, and ordered the treasure returned.

Odyssey argued that the wreck was never positively identified as the 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. International treaties generally hold that warships sunk in battle are protected from treasure seekers.

The company blamed politics for the courts’ decisions since the U.S. government publicly backed Spain’s efforts to get the treasure returned. In several projects since then, Odyssey has worked with the British government on efforts to salvage that nation’s sunken ships, with agreements to share what it recovers.

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