A US judge has ruled that Florida based Odyssey Marine Exploration Company must return more than half-million silver and gold coins it found as sunken treasure on a 19th century warship to the Spanish government. The 17 tons of coins and other items are valued at more than $500 million and is the biggest sunken treasure recovery in history.

The treasure was recovered in 2007 from the Spanish galleon Nuestra Senora de las Mercedes (Our Lady of Mercy). The British Navy sank the boat in 1804 off the coast of Portugal as the galleon was returning to Spain from Peru.

The US Supreme Court refused to overturn the lower court’s decision and ruled that the treasure belonged to Spain. Odyssey had claimed it cost $412,814 for preserving and storing the booty in a Tampa warehouse while it fought lawsuits with the Spanish and Peruvian governments over property rights to the treasure.. The judge ruled that Spain does not have to reimburse the deep sea recovery firm for any costs for preserving and storing the treasure. US Judge Mark Pizzo ruled the court does not have the authority to rule on the find and ordered the treasure must be accessible to Spain by Tuesday the 21 February 2012 and be transferred to Spain by Friday February 24.

Odyssey claimed the discovery was made in international waters in the Atlantic, but refused to reveal the location of the wreck they had codenamed Black Swan. The Spanish were furious when Odyssey announced the find and in October 2007 the Spanish navy intercepted the 250ft Odyssey Explorer off Gibraltar and escorted the boat to Algeciras to be searched. The Spanish searched the crew and confiscated computer hard drives. However, by then Odyssey had already flown the treasure from Gibraltar to its base in Tampa, Florida.

The Spanish argue that apart from being a national treasure it is also the grave to 250 Spanish sailors who died on board. They said Odyssey carried out the salvage operation in secret after being warned that it was illegal. They say the galleon is protected by 'sovereign immunity' which prohibits the unauthorised disturbance or commercial exploitation of state-owned naval vessels.

Odyssey is now searching for the 80-gun English warship Sussex sunk in 1664 with seven tons of gold on board. The search has the backing of the British government. However the waters where it is supposed to have gone down are claimed by the Spanish.

Odyssey said it will appeal and hopes to involve descendants of the galleon's crew.