The beds of the world’s oceans are littered with shipwrecks. In fact estimates put the figure at somewhere in the region of 3 million – and yet with 70 per cent of the world’s surface covered by ocean and recorded depths of up to seven miles, it is no great surprise that some of history’s most famous shipwrecks have lain undiscovered since the day they went down. That certainly hasn’t stopped marine archaeologists, historians, divers and commercial treasure hunters from searching for them – and yet in a world of rapidly dwindling mystery, the ocean’s depths continue to tease us with stories we can’t resolve. What follows are five of the greatest, most famous and most significant shipwrecks that remain hidden to this day...

(1) The Merchant Royal

While Britain’s busy and often treacherous seas are excellent for wreck diving, you don’t tend to find anything of enormous value here.

The Merchant Royal: Top 5 undiscovered shipwrecks

Freighting a haul of coins and precious metals to England from Mexico in 1641, the discovery of the wreck of the 'Merchant Royal', believed lost between the Isles of Scilly and Land's End would be worth hundreds of millions of pounds in today's coin.

For chests full of gold you tend to have to head for the sunny, colonial bolt-holes of the big naval empires - and yet somewhere off the west coast lies a ship called the 'Merchant Royal'. It was lost between the Isles of Scilly and Land’s End in 1641 en-route from Mexico to Dartmouth with a cargo of coins and bullion that would be worth hundreds of millions of pounds in today’s money. There was talk of it having been located in 2007 by a specialist salvage company called Odyssey Marine Exploration. They discovered a relatively large haul of treasures - and yet after a protracted legal battle, the company was forced to hand some of the recovered coins to Spain, suggesting that they had in fact unearthed a Spanish galleon. For now at least, it seems the infamous 'Merchant Royal' remains firmly hidden from view.

(2) Flor do Mar

The 'Flor do Mar' was a carrack (a Portuguese three or four-masted ship designed for oceanic expeditions) – and at the time, its 400-ton bulk made it the largest of its kind.

Flor do Mar: Top 5 undiscovered shipwrecks

Widely held to be the most valuable shipwreck on earth, this Portuguese carrack was laden with treasure from the King of Siam but sank after being caught in a storm in the Straits of Malacca.

It was in 1511, nine years after its construction, that it was returning from the conquering of Malacca under the hand of its nobleman Skipper, Alfonso de Albuquerque, when it met its end. It was weighed down not just with the spoils of war, but with offerings from the King of Siam (Thailand) to the Portuguese monarchy. Historical testimony suggests it was a truly vast hoard of riches – and yet the ship (which was by now not in the best of shape) was caught out by a storm in the Straits of Malacca and shipwrecked on the Sumatran shoals. Despite a cruel death toll, the Skipper himself was rescued but the ship disappeared to the seabed. It is widely deemed to be the single most valuable wreck in the world - but despite numerous attempts to locate it, no sign has yet been found.

(3) Las Cinque Chagas

'Las Cinque Chagas' (named after the five wounds of Christ) was a vast ship by the standards of the age.

Las Cinque Chagas: Top 5 greatest undiscovered shipwwrecks

Supposedly resting in deep water off the coast of the Azores, 'Las Cinque Chagas' is conservatively estimated to be worth US$1 billion due to her cargo of precious stones and metals.

This Portuguese carrack was 150 feet long and 45 feet wide; it weighed in at 1,200 tons and it carried around 1,000 people. However, when it was sunk by the British in 1594 en-route from Goa to Lisbon, it was laden with a cargo that compelled people to call it the richest ship ever to set sail from the East Indies. Probably unaware of the scale of its hoard, a posse of British pirate ships under the patronage of the Earl of Cumberland (the 'Mayflower', the 'Royal Exchange' and the 'Sampson') attacked her for several days before she finally went down in deep waters off the coast of the Azores. It was reportedly stuffed to the rafters with precious stones (rubies, pearls and diamonds) and precious metals. In fact, even conservative estimates put the value of the wreck at well over a billion US dollars in today’s money. Anyone fancy joining me in a treasure hunt...

(4) USS Indianpolis

In all of history, few sinkings can have been as brutal, drawn out or barbaric as that of the 'USS Indianapolis'. Having carried ‘Little Boy’ (the nuclear bomb that would later be dropped on Hiroshima) from San Francisco to the remote Pacific island of Tinian, this WWII Portland Class Cruiser was sunk somewhere between Guam and the Philippines.

USS Indianapolis: top 5 greatest undiscovered shipwrecks

A series of blunders by the US Navy led to hundreds of unnecessary deaths in 1945 after the 'USS Indianapolis' had successfully delivered the atomic bomb to the island of Tinian.

It was reportedly hit by a trio of Japanese torpedoes at the end of July, 1945 – and although 300 of the 1,196-strong crew went down with the ship, another 579 would die in the water over the next four days, some by drowning but the vast majority by shark attack. According to contemporary accounts, mistakes were made – firstly by a drunk operative at a Naval Signal Station, who managed to ignore the ship’s distress signal; and secondly by a failure to follow up on her overdue arrival in port. In short, by the time the Navy recognised that she had been sunk, only 317 men remained alive. Rather shamefully, the Navy tried to use the ship's captain, Charles McVay, as a scapegoat – and although he was later exonerated, it would eventually lead to his suicide in 1968.

(5) The Santa Maria

We finish with the flagship of Christopher Columbus – the famous 'Santa Maria'. Along with two smaller ships, the 'Niña' and the 'Pinta', the 'Santa Maria' took Columbus on his exploratory expedition to the New World in 1492, ushering in the colonisation of the Americas by European settlers.

Santa Maria: top 5 greatest undiscovered shipwrecks

The flagship of Christopher Columbus' voyage of discovery across the Atlantic to North America was lost on Christmas Day, 1492, after drifting on to a reef and being holed.

Born in Genoa but funded by Spain, it was on Christmas Day in 1492 that Columbus’s flagship drifted onto a reef and was holed. Rumour has it that some heavy drinking contributed to the sinking. Now a wreck has apparently been discovered off the north coast of Haiti by renowned underwater explorer Barry Clifford - and while Mr Clifford has reportedly stated that all the “geographical, underwater topography and archaeological evidence” supports his belief that he has in fact found the Santa Maria, precedent suggests that until proven beyond doubt, such confidence can often be misplaced. For now then, on account of its historical significance (and in the absence of demonstrable proof), the grand old 'Santa Maria' keeps her place as one of the world’s truly great undiscovered wrecks.

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Written by: Alex Smith
Alex Smith is an ex-Naval officer, with extensive experience as a marine journalist, boat tester and magazine editor. Having raced as a Pilot in the National Thundercat Series and as a Navigator in the inaugural Red Sea RIB Rally, he has now settled in the West Country, where he lives and works as a specialist marine writer and photographer from his narrowboat in Bath.