In the early 2000s, the British government abandoned plans to recover an estimated £5.5 billion treasure from a suspected Royal Navy shipwreck—believed to be HMS Sussex—to avoid escalating diplomatic tensions with Spain, according to leaked diplomatic cables.

HMS Sussex, a flagship of the Royal Navy lost off Gibraltar in 1694, is thought to be carrying up to 10 tons of gold coins intended for Victor Amadeus II, Duke of Savoy, to fund his efforts against King Louis XIV during the Nine Years’ War. The treasure’s estimated value makes the shipwreck potentially one of the most valuable maritime discoveries in history.

Following a three-year search, US-based company Odyssey Marine Exploration announced in 2001 that it was “99 percent” certain it had located the shipwreck about 821 metres beneath the Mediterranean Sea near Gibraltar. The British government initially authorized an agreement with Odyssey to identify, excavate, and recover the wreck, with any treasure to be shared.

However, the project soon encountered resistance from Spain, which asserted authority over the surrounding waters despite HMS Sussex’s status as a British warship. Spain’s claim was tied to its longstanding dispute over Gibraltar, an overseas British territory claimed by Madrid. Spanish authorities reportedly intervened to obstruct the salvage effort, with former diplomatic cables revealing Spain’s culture minister at the time, Carmen Calvo, declaring that Odyssey would only search for the wreck “over her dead body.”

British officials privately expressed concern over the dispute’s impact on diplomatic relations. Dame Denise Holt, then deputy head of mission at the British embassy in Madrid, described the situation as an “unnecessary threat” to bilateral ties and indicated that the government was considering terminating the agreement with Odyssey to ease tensions.

The wreck reportedly lies east of Gibraltar in international waters, an area Britain has never formally claimed. While international maritime law permits coastal states to claim up to 12 nautical miles of territory, the UK has traditionally limited Gibraltar’s territorial waters to three nautical miles. Critics argue this limited claim left the salvage operation vulnerable to Spanish interference. Neil Cunningham Dobson, the marine archaeologist on the project, described repeated disruptions by Spanish patrol boats, which he said ultimately doomed the expedition.

Odyssey’s efforts were further complicated after the company recovered hundreds of thousands of silver coins from another wreck, the Black Swan, which sparked a legal dispute with Spain and deteriorated relations between the two countries and the salvage firm.

Despite the past challenges, the wreck remains British property under international law. Advances in underwater technology, including autonomous underwater vehicles and improved survey equipment, have renewed hopes that a new salvage operation could succeed. Odyssey Marine Exploration’s parent company, American Ocean Minerals, has indicated it would consider resuming the mission if it received government approval.

HMS Sussex’s sinking in February 1694 resulted in the loss of nearly all its 550 crew members, including Admiral Sir Francis Wheler. Contemporary accounts and archival evidence indicate the ship was carrying significant funds for England’s European allies, further underscoring the historical and financial importance of the wreck.

The UK Ministry of Defence declined to comment on the matter.