The 1985 discovery of the RMS Titanic marked the end of one of the most famous hunts in underwater archeology, but many other historically significant shipwrecks continue to elude scientists and salvage teams. From Christopher Columbus’ flagship to one of the most legendary commerce raiders of the American Revolution, learn the stories behind six vessels whose watery graves are still missing in action.

Santa Maria

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Model of the Santa Maria. (Credit: SPL/Getty Images)

Christopher Columbus famously set sail on his first voyage to the New World with three ships—the Niña, the Pinta and the Santa Maria—but only two returned to Spain. On Christmas Eve 1492, the sailor charged with steering the flagship Santa Maria handed the wheel over to an inexperienced cabin boy, who promptly ran the vessel onto a coral reef near modern day Haiti. Crewmen managed to empty the ship of its cargo with the help of local natives, but it sank the following day and may have later been buried by sediment. Its precise location has since been lost to history. Underwater explorer Barry Clifford made headlines in 2014 after he claimed to have found the Santa Maria using information from Columbus’ journals, but an examination by UNESCO experts later found proof that the wreck belonged to a different ship from the 17th or 18th centuries.

USS Indianapolis

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USS Indianapolis in 1939.

On July 30, 1945, just a few days after it successfully delivered components for the first atomic bomb to an American base on the island of Tinian, USS Indianapolis was nearly ripped in half by a double torpedo strike from the Japanese submarine I-58. The unescorted heavy cruiser disappeared beneath the surface in a matter of minutes, taking some 300 seamen with it. The remaining 900 sailors were left bobbing helplessly in the shark-infested waters of the Philippine Sea. By the time they were accidentally spotted by a Navy plane and rescued four days later, all but 317 had perished from exposure and attacks by prowling hordes of oceanic whitetips. The sinking of Indianapolis is now remembered as the worst American naval disaster of World War II. Yet despite multiple expeditions using sonar and underwater vehicles, the ship’s wreckage has never been found. Part of the problem lies in the extreme depths of the search area. According to some estimates, the cruiser may rest in over 12,000 feet of water.

HMS Endeavour

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Replica of HMS Endeavour in Sydney Harbor. (Credit: Getty Images)

HMS Endeavour is most famous for carrying Captain James Cook around the globe during his first voyage of discovery from 1768 to 1771. The ship was the first European vessel to visit the east coast of Australia and circumnavigate New Zealand, but only a few years after returning home, it was unceremoniously sold to a private buyer and renamed the Lord Sandwich. It was later chartered by the British Royal Navy and used to ferry troops to New England during the American Revolution. While moored in Rhode Island’s Newport Harbor in 1778, it became one of 13 vessels that were intentionally sunk to form a blockade against an approaching French fleet. The ship’s decaying remains are now the target of an ongoing search by the Rhode Island Marine Archaeology Project and the Australian National Maritime Museum, which have spent several years mapping and exploring the silt-laden waters around Newport. The team has located more than two-thirds of the scuttled ships as of this year, but they have yet to find hard evidence that any of them is Cook’s long lost Endeavour.

The Griffin

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Lake Michigan. (Credit: Getty Images)

The first sailing ship to cruise the Great Lakes, Griffin was a three-masted vessel built by the French explorer Rene-Robert Cavelier, Sieur de La Salle during an early expedition to the North American frontier. La Salle used Griffin to travel the Niagara River and explore parts of Lake Erie, Lake Huron and Lake Michigan, but the ship later disappeared in September 1679 after setting sail from present-day Green Bay with six crewmen and a cargo of furs. Its true fate remains a mystery, though it’s commonly believed that the ship may have foundered in a storm or been scuttled by a mutinous crew. Legions of searchers have tried to track down its watery grave, but so far none of their discoveries has been confirmed to be the so-called “holy grail of Great Lakes shipwrecks.” One of the most recent false alarms came in 2014, when two treasure hunters were reported to have found the fabled ship in the waters of Lake Michigan. Unfortunately, a subsequent investigation revealed that the wreck was most likely a steam-powered ship from the 19th or 20th centuries.

Shackleton’s Endurance

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Shackleton’s ship, Endurance, as it lay locked in the Weddell Sea. (Credit: Archives/Getty Images)

In 1914, Ernest Shackleton set sail from England on his Imperial Trans-Antarctic Expedition to the South Pole. The Irish-born explorer hoped to make the first overland crossing of Antarctica, but before he ever set foot on the continent, his ship Endurance became trapped in heavy pack ice in the Weddell Sea. True to its name, the wooden barquentine survived 10 months in the frozen vise before the pressure finally cracked its hull and sent it tumbling to the seafloor. While Shackleton would later lead his crew to safety by making a perilous 800-mile voyage in a lifeboat, Endurance remains lost in the frigid deep to this day. The ship is now believed to lurk at a depth of some 10,000 feet beneath a 5-foot layer of ice. The likes of underwater salvage expert David Mearns and Titanic discoverer Robert Ballard have expressed interest in hunting it down, but no team has yet to scrape together funding for an Antarctic expedition.

Bonhomme Richard

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Bonhomme Richard battling Serapis.

Few Continental Navy ships chalked up a more distinguished combat record than Bonhomme Richard. A French donation to the Patriot cause, the aging frigate set sail in 1779 under Captain John Paul Jones and proceeded to capture 16 British vessels in a matter of weeks. On September 23, it squared off against HMS Serapis and another Royal Navy ship in a ferocious battle off the northeast coast of England. Brushing off an early call to surrender with the immortal words “I have not yet begun to fight,” Jones rallied his men and successfully captured Serapis after several hours of combat. Unfortunately, his victory came too late for Bonhomme Richard, which had caught fire during the exchange and taken several shots below its waterline. After spending 36 hours trying to keep it afloat, Jones and his crew reluctantly abandoned the ship and let it sink in the choppy waters of the North Sea. Its wreckage has since become the target of expeditions by everyone from British locals to professional salvage companies, the U.S. Navy and even author and adventurer Clive Cussler. A few of the teams have found wrecks matching the Bonhomme Richard’s description, but none of them has yet been identified as the missing ship.