The treasure arrives at its original destination Saturday, 208 years behind schedule.
Two Spanish cargo planes departed MacDill Air Force Base on Friday bound for Madrid with $500 million in booty once carried by a Spanish galleon that sank off the coast of Portugal in 1804.
The treasure, weighing 17 tons, might be the richest shipwreck prize in history.
Recovered by Tampa-based Odyssey Marine Exploration in 2007, the flight marked the end of a bruising legal battle the company lost to Spain over possession of 594,000 silver coins and other artifacts.
Spain's ambassador to the United States, Jorge Dezcallar, told more than two dozen reporters and camera crews that Spain was finally reclaiming what was rightfully hers.
"We bear witness to that fateful day 200 years ago," he said. "This is about our historical heritage. . . . History makes us who we are, and today we are witnessing the end of a journey that started 200 years ago. . . . It is our duty to end that mission successfully."
He said the treasure will eventually be displayed in museums in Spain and elsewhere. "This is not money to be sold," the ambassador said.
Officials at Odyssey Marine, which spent $2.6 million salvaging, transporting and storing the treasure, declined to comment. But in a statement earlier, Greg Stemm, Odyssey's co-founder, said, "People won't stop looking for Spanish shipwrecks. They will just stop reporting their finds. . . . No archaeology will be done."
The company will receive no compensation from Spain for its recovery of the coins.
Spain believes the coins were recovered from the wreck of the Nuestra Senora de las Mercedes. The ship was sunk by British warships as it sailed from South America. More than 200 people went to the bottom with it.
But Odyssey officials say the wreck was never positively identified as the Mercedes, casting doubt on Spain's claim.
A federal judge in Tampa ruled for Spain in 2009.
"The ineffable truth of this case is that the Mercedes is a naval vessel of Spain and that the wreck of this naval vessel, the vessel's cargo, and any human remains are the natural and legal patrimony of Spain . . . despite any man's aspiration to the contrary," the judge's ruling said.
Earlier this month, U.S. Supreme Court Justice Clarence Thomas rejected a bid to reverse a lower court ruling that Odyssey give up the treasure.
Odyssey, which uses remote-control vehicles to help recover undersea wrecks, called its Mercedes project "Black Swan."
Spain argued that the recovery of the treasure amounted to a disturbance of a historic site.
Javier Romero, a rear admiral in the Spanish navy, said, "Our sunken ships are . . . sacred places. They are cemeteries. . . . We prefer to leave the ships as they are."
James Goold, a Washington lawyer representing Spain, was asked if Spain should express its "gratitude" to Odyssey for recovering the treasures.
What if Spain, Goold said, took a relic from the sunken battleship Arizona at Pearl Harbor?
"Would the United States have gratitude then?" he said.
Friday's event may have been unprecedented for MacDill, which has hosted presidents, diplomats and its share of odd cargo through the years, but perhaps never before silver bullion.
The treasure, packed in white buckets wrapped in black plastic, arrived from an undisclosed location in Sarasota.
Local television stations used a helicopter to try to capture the transfer from Sarasota to Tampa. As the treasure arrived at MacDill, base officials took it to a hanger.
Air Force guards toting M-4 rifles stood between reporters and the two C-130 aircraft carrying the coins.
After a brief news conference, the media were led to an opening by the back of the aircraft to photograph pallets carrying the treasure. But the coins themselves were not visible.
A reporter asked the ambassador if Spain was trying to quickly spirit the treasure out of the United States to avoid further legal trouble.
With the treasure lost for two centuries, the question seemed to flummox Dezcallar.
"This," he said, "is not quickly."
William R. Levesque can be reached at [email protected]