Long-lost Captain Cook's Endeavour likely to remain US property

The replica Endeavour.

If Captain James Cook's Endeavour really has finally been found off Rhode Island, what remains of it will likely remain forever more in the United States.

Marine archaeologists are expected to announce a breakthrough in the 25-year search for the historic vessel on Friday.

It's believed the ship's final resting place is in Newport Harbour, off Rhode Island, on the northeast coast of the US. The search has been narrowed down to an area just off the Goat Island shore near Gurneys Resort.

The announcement also happens to be days out from the 250th anniversary of the famed explorer's departure on the Endeavour from Plymouth on August 25, 1768, to claim Australia and New Zealand for England.

The New Zealand Archaeological Association's president, Katharine Watson, says it's "incredibly exciting" news and is considered a key part of the discovery of New Zealand.

Watson was quick to dismiss there being a legal battle over who gets it.

"From my perspective there are certain legal obligations... [it] seems like it legally belongs to Rhode Island, so I guess that's where it would stay."

She adds there probably isn't a "great deal of it left to see".

"They don't know what condition it's going to be in.

"Salt water environment is pretty harsh on timber... all of those things need to be taken into consideration," Watson says.

Archaeologists from the Australian National Maritime Museum (ANMM) and the Rhode Island Marine Archaeology Project (RIMAP) will release a 3D photogrammetric image of the site at the official announcement in the US later this week.

But the origins of the ship can't be confirmed until its remnants are excavated - which researchers expect will happen next year.

The Endeavour was purchased by the British Navy in 1768 and navigated by Cook to claim Australia — then known as Terra Australis — for the British during his historic voyage.

It became the first ship to reach the east coast of Australia when Cook arrived at the site now known as Botany Bay in 1770.

The ship was later renamed the Earl of Sandwich 2 and last seen in 1778 while being used for transportation purposes during the American War of Independence.

Researchers believe the Endeavour was part of a fleet of 13 ships scuttled by the British during the revolutionary war to blockade Newport Harbour from the French.

RIMAP started studying sunken British transports in Newport Harbour in 1993 with a remote sensing survey.

There were 13 potential vessels that could have been the Endeavour but the search has recently narrowed to possibly "one or two archaeological sites", RIMAP said in a press release.