Researchers in the US believe they may be a step closer to locating the ship in which British explorer Captain James Cook sailed to Australia in 1768.
The Rhode Island Marine Archaeology Project (Rimap) has known for some time the ship was scuttled in Newport Harbour in 1778.
But they now believe they have narrowed down the search to a cluster of five shipwrecks on the seafloor.
The researchers plan to investigate the ships and their artefacts further.
They are also appealing for funds to build the right facilities for handling and storing items retrieved from the sea.
"All of the 13 ships lost in Newport during the Revolution are important to American history, but it will be a national celebration in Australia when RIMAP identifies the Lord Sandwich ex Endeavour," the researchers said in a statement.
Rimap is a non-profit organisation set up 1992 so that the "diving and non-diving public" could study maritime history and marine archaeology sites in Rhode Island's Narragansett Bay, according to its website.
Capt Cook set sail on Endeavour - a British-built coal ship - in 1768 on a scientific voyage to map the Pacific Ocean.
In 1770 he arrived off the south-east coast of what is now Australia, eventually making landfall at Botany Bay.
He later claimed the region for the British crown, despite the presence of large Indigenous communities.
After sailing back to Britain, the Endeavour was renamed Lord Sandwich and became a troop carrier ship.
During the American War of Independence it was scuttled by the British Navy in a blockade of the Narragansett Bay.
The wreckage has never been found, but the Rimap researchers have been investigating 13 sunken ships, with the help of remote sensing equipment and historical documents.
They said an analysis of data suggests there is "an 80 to 100% chance" that the Lord Sandwich wreckage is still in Newport Harbor, "and because the Lord Sandwich was Capt Cook's Endeavour, that means RIMAP has found her, too".
They plan to outline their plans for confirming the find at a news briefing on Wednesday.
The announcement coincides with the 240th anniversary of Rhode Island declaring independence from the UK.
Rimap said closing in on identifying "one of the most important shipwrecks in world history" would be "an intriguing birthday gift for all of Rhode Island".