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One of two British explorer ships that vanished in the Arctic nearly 170 years ago during an expedition to find the fabled Northwest Passage has been found, Canada's prime minister announced Tuesday in a discovery that could unlock one of history's biggest mysteries and swell Canadian pride.

Last seen in the 1840s while under the command of Sir John Franklin, HMS Erebus and HMS Terror have long been among the most sought-after prizes in marine archaeology and the subject of songs, poems and novels.

Prime Minister Stephen Harper's office said the well-preserved wreck of one of the vessels was found Sunday 11 meters (yards) below the surface with the help of a remotely operated underwater vehicle.

Harper said that it is unclear which ship was found, but that sonar images yielded enough information to confirm it is one of the pair.

"This is truly a historic moment for Canada," said Harper, who was beaming, uncharacteristically. "This has been a great Canadian story and mystery and the subject of scientists, historians, writers and singers, so I think we really have an important day in mapping the history of our country."

Harper said the discovery would shed light on what happened to Franklin's crew.

Franklin and 128 hand-picked officers and men had set out in 1846 to find the Northwest Passage, the long-sought shortcut to Asia that supposedly ran from the Atlantic to the Pacific by way of the harsh, ice-choked Arctic.

Historians believe that the ships were lost in 1848 after they became locked in the ice near King William Island and that the crews abandoned them in a hopeless bid to reach safety. Inuit lore tells of "white men who were starving" as late as the winter of 1850 on the Royal Geographical Society Island.

Dozens of searches by the British and Americans in the 1800s failed to locate the wrecks, and some of those expeditions ended in tragedy, too. But they opened up parts of the Canadian Arctic to discovery and ultimately spied a Northwest Passage, though it was inhospitable to shipping because of ice and treacherous weather.

Canada announced in 2008 that it would look for the ships, and Harper's government has poured millions into the venture, with the prime minister himself taking part in the search.

Harper's government made the project a top priority as it looked to assert Canada's sovereignty over the Northwest Passage, where melting Arctic ice in recent years has unlocked the very shipping route Franklin was after.

Canada says it owns the passage. The U.S. and others say it is international territory.

Ryan Harris, an underwater archaeologist helping to lead the Parks Canada search, said a sonar image shows some of the ship's deck structures, including the main mast, which was sheared off by the ice when the vessel sank. He said the contents of the ship are most likely in the same good condition.

The exact location was not disclosed for fear of looters.

The discovery comes shortly after a team of archeologists found a tiny fragment from the doomed expedition -- an iron fitting that once helped support a boat from one of the ships.

Other tantalizing traces have been found over the years, including the bodies of three crewmen discovered in the 1980s. Those included the perfectly preserved remains of a petty officer in an ice-filled coffin.

The search for an Arctic passage to Asia frustrated explorers for centuries, beginning with John Cabot's voyage in 1497. The shortcut eluded other famous explorers, including Henry Hudson and Francis Drake.

No sea crossing was successful until Roald Amundsen of Norway completed his trip in 1903-06.