One of the most famous ships lost in the 19th century has been located in the Arctic, the Canadian government announced Tuesday, prompting Prime Minister Stephen Harper to declare that "one of Canada's greatest mysteries" has been solved.

The shipwreck marks the final resting place of one of two vessels that disappeared mysteriously nearly 170 years ago, when a British naval expedition led by Sir John Franklin was attempting to navigate and map the Northwest Passage.

The ships, the H.M.S. Erebus and H.M.S. Terror, were lost in 1846 and both crews perished. Although the graves of a few of the men were discovered later on land and local Inuit reported seeing one of the ships sink, exactly what happened to the ill-fated voyage has been a source of intense debate and speculation over the years. (See "5 Shipwrecks Lost to Time That Archaeologists Would Love to Get Their Hands On.")

But now Canadian authorities have released sonar images of what appears to be a largely intact ship near Nunavut's King William Island, thanks to a remotely operated vehicle owned by Parks Canada.

"There is no doubt" that the ship is either the Erebus or Terror, says James Delgado, a maritime and shipwreck historian with the National Oceanic and Atmospheric Administration. Delgado had previously looked for the ships in the Arctic but was not involved with Canada's efforts, which he said were "years in the making."

"I think this will prove to be one of the great maritime archaeological discoveries of our time," says Delgado, who wrote the book Across the Top of the World: The Quest for the Northwest Passage.

View Images Led by Sir John Franklin in the mid-19th century, the ships H.M.S. Erebus and H.M.S. Terror were lost in an ill-fated attempt to discover the Northwest Passage. One of them has now been found. Illustration by London News via Getty Images

Doomed Expedition

According to Delgado, the Franklin expedition was one of the best equipped and most experienced voyages to tackle the Northwest Passage in the mid-19th century. Finding a route across the top of North America was long seen as a holy grail in navigation that would provide a quicker route from the Atlantic to the Pacific.

"It wasn't quite mounting a mission to the moon, but it was darn close," he said.

The expedition sailed from England in 1845. The ships met whalers as they entered the chilly waters around northern Canada. Then an expectant world outside was met with silence.

"It turned out to be one of the most compelling 'what happened' stories," says Delgado. Numerous rescue and then archaeological attempts were made in the ensuing years, by teams from several countries.

A few graves of crew were eventually found on Beechey Island. Cut marks left on human bones found on King William Island have been interpreted to suggest the survivors practiced cannibalism.

A note left by a crew member said Franklin had died and the ships had been abandoned, but didn't give any details. Inuit said they saw one of the ships sink rapidly into the water, but later historians argued that the vessels were more likely dashed to bits by the ice. (See "Artifact Trove on Deepest Shipwreck Explored Off U.S.")

Hopes for Cold Water

Delgado says the fact that the shipwreck appears to be largely intact is great news for learning more about what happened to the expedition.

There is a good chance that books and letters on board may have been preserved in the cold water, he said. And the crew was known to have daguerreotype equipment. "We know those photographic plates have survived on other shipwrecks in cold conditions, so who knows what might be on them?" asks Delgado. (See "Shipwrecks Removed From Protected Coral Reefs.")

He adds that the ship is likely to be a "time capsule" that sheds light not only on what happened to its crew, but also on the era. Uncovering that trove has been a big challenge over the years, thanks to cold temperatures, pack ice, and the vastness of the remote area.

"If the Canadians decide to do more research, I think this ship will begin to speak for those men, or if we can find their writings, they'll speak for themselves," Delgado says.

In announcing the discovery, the prime minister said Franklin's ships "are an important part of Canadian history, given that his expeditions ... laid the foundations of Canada's Arctic sovereignty."