Archaeologists are getting closer to confirming the discovery of Captain Cook's Endeavour at the bottom of a US harbour, with scientific testing and clues found by dive teams raising hopes it is the historic vessel.
A joint US-Australian effort has been underway for more than a year on a shipwreck in Newport Harbour, Rhode Island.
Archaeologists and dive teams are yet to find anything about the wreck's structure that would rule it out as the ship Captain Cook sailed, on his historic voyage to Australia and the South Pacific from 1768 to 1771.
"We have definitely entered that exciting phase now," Australian National Maritime Museum director Kevin Sumption told AAP on Sunday.
An event was held in Rhode Island on Sunday to announce the latest developments in the search for the Endeavour.
An announcement confirming the shipwreck as the Endeavour - or not - could be made around Christmas when independent scientific testing on the keel and other pieces are completed.
The Endeavour's colourful history continued after Captain Cook's expedition.
The vessel was re-fitted into a transport ship, renamed the Lord Sandwich II, and used by the British against rebelling American colonists during the American War of Independence.
The Brits sunk the Lord Sandwich II and 12 other ships in Newport Harbour in 1778 as a tactic to block the French Navy, allies of the Americans, from entering.
The Rhode Island Marine Archaeology Project has led the search for the Lord Sandwich II/Endeavour and joined forces with the ANMN and SilentWorld Foundation.
Mr Sumption said positive clues so far pointing to the vessel as the Endeavour include divers finding a hole in the ship confirming it had been scuttled, just as the Lord Sandwich II had been in 1778.
Wood samples taken from the ship were independently analysed and all returned as English white oak, consistent with the Endeavour's building materials.
Divers have also found two exposed cannons and in the next week will look for two more.
The ship's keel will likely be the key to confirming if it is the Endeavour.
The keel was made of elm and no other ship scuttled in the harbour at that time had an elm keel.
"The forensic wood sampling we will be doing over the next couple of months will be rather critical," Mr Sumption said.
"If this particular piece of the keel turns out to be elm, that will be part of the puzzle that kind of allows us to say 'Yes, this is Endeavour'."
The search teams will also be looking for evidence of another distinguishing feature - the Endeavour's "deadwood Keelson" construction characteristic.
It will be ironic if the Endeavour's unique elm keel is the key to unlocking the mystery.
It was off Newport Harbour in 1983 where the most significant keel in Australian sporting history, Australia II's winged keel, performed its magic to win the America's Cup and end America's 132-year stranglehold on the event.
Australian Associated Press