Sir John Franklin's ill-fated expedition to the Arctic may have found the Northwest Passage, the man who discovered his shipwreck said.
The fabled Erebus commanded by the British explorer was traced to the icy waters north of Canada last year.
Sir John led two ships and 129 men in 1845 to chart the new route to the Indies trading nations of Asia. They were never seen alive by a European again.
Parks Canada's Ryan Harris spearheaded efforts to find the wrecks and is planning a further dive to the Erebus next month.
He said: "We hope to be able to identify archaeologically whether the ship was re-manned as the Inuits seem to indicate.
"If the ship was re-manned there is a significance to that, they must have seen a navigable route (through the Northwest Passage), this would prove it.
"If they were on board this ship they would have known that they had done it."
The loss of HMS Erebus and HMS Terror prompted one of the largest searches in history.
The expedition's disappearance became one of the great mysteries of the age of Victorian exploration.
Experts believe the ships were lost when they became locked in the ice near King William Island and that the crews abandoned them in a hopeless bid to reach safety.
Reports at the time from local Inuits said the men, desperate for food, resorted to cannibalism before they died.
In 1997 the bones of crew discovered on King William Island were found to have cut marks consistent with the men having been cut up and eaten.
The Canadian government began searching for Franklin's ships in 2008 in a dispute over the sovereignty of an area made more viable as a trading route because of global warming increasing ice melt.
Mr Harris, senior marine archaeologist for the Canadian Government, led the party which found the Erebus last year and is returning next month, he told an audience in Banbridge, Co Down.
He will spend three weeks in the inhospitable Canadian Arctic and the Canadian armed forces will support his team with giant Hercules aircraft landing on the thick ice using skis.
Nineteen divers will work from sunrise to sunset and Mr Harris said he hoped they would get ten days of diving out of the three week expedition.
"We are dovetailing our interest with the military which has sovereignty considerations.
"We are trying this live video feed so people could experience it in real time.
"The public interest in the expedition is huge."
The divers will be seeking answers to some intriguing questions.
Mr Harris said: "Did the discipline breakdown, at what point did it occur to people to try it alone? Were there officers at the end?
"The bell rang every half an hour, the changing of the ship's watches, at what point in time would they have not rang the bell, when the progress of time had no meaning, when there was little hope of returning home again?"
He said the Inuit reported that there were tins of unopened food on board, and analysis could shed light on whether the men were poisoned by tainted meat.
The archaeologist also questioned whether there was any coal left or were they burning furniture.
"I tend to think it sailed in May 1845 when Franklin received his orders from the admiralty to proceed ... directing the expedition to among the worst ice choke holds on Earth, a place where even Inuit would seldom travel because there is nothing to live on.
"Spending two years in those conditions did not give them much of a chance."
Mr Harris's team will be establishing a camp in the ice over the site and diving through it.
They will have to bore through six feet of ice, a process taking half a day, and travel down to the wreck 11 metres below the surface.
"There is a distinct possibility of written records on the ship, there is a very good chance that we will find the records, maybe only fragments."
At that time pages were made of linen.
He said large parts of the boat were covered in kelp. "We will be looking to give the side a thorough haircut to reveal a lot of the bits that are camouflaged from view."
He said they would use a laser scanning system to give crystal-clear records of complex structures in great depth.
The search party found the Erebus last September after discovering wreckage on a nearby island.
Mr Harris said: "Everything was quite cloudy, you could not even tell exactly what direction the ship was."
The divers found some of the ship's timbers detached from the hulk and followed them towards the wreck.
"Then this enormous, stately shipwreck lying bolt upright loomed out of the haze."
He peered into the interior of the ship as part of the deck had been ripped off by ice.
"You could not help feel this overwhelming sense of privilege, it is a hallowed place, where these men spent their last desperate hours suffering incredible privations and making the ultimate sacrifice."
They found a table leg which may have been from Franklin's cabin, to judge by an image contained in a newspaper article from the time.
They also saw a tiller, anchors and a glass prism used to distribute light over an officer's writing desk, possibly in Franklin's bedchamber.
"If the entire ship is a time capsule each cabin is distinct and offers a time capsule representing the shipboard life of an individual, their personal possessions and perhaps journals they may have kept on board," he said.
They also discovered the exit flue for a cabin stove where officers would have eaten, attempting to escape the biting cold and endless darkness of the polar north, as well as a mast and rigging.
A brass cannon was lying on the sea floor nearby.
Nearly everything was covered by markers signifying it was Royal Navy property, down to the smallest pieces of equipment.
Mr Harris said the ship was still in the ownership of the Royal Navy but a memorandum of understanding had been signed giving Canada custody but not establishing a precedent for other finds.
The marine archaeologist said raising the ship would not be a straightforward undertaking. It would be expensive and difficult to treat all the timbers, but it was doable.
He said: "At a time when all options are on the table and being considered, generally we would prefer to leave this wreck on the sea floor. Being a remarkable shipwreck with an incredible national and international level of interest it is a national historic site.
"It has regional and local significance to the Inuit and derives a lot of significance from its historical context and that would change if it is plucked up from the sea floor, we have to see what the best answer is."