The ghostly shape of a British warship that sank with all hands more than 200 years ago has been discovered at the bottom of Lake Ontario, close to the shores of New York state.

The ship, HMS Ontario, is the oldest vessel to be found on the floor of the Great Lakes, a graveyard for more than 4,700 ships.

It has been located after a three-year search by two explorers using scanning sonar and an unmanned mini-submarine.

The 80ft sloop of war sank with more than 120 men, women, children and prisoners on board during the American revolutionary war in October 1780. Bad weather rather than cannon fire put paid to her. As she was crossing the lake from Fort Niagara a gale swamped her decks and sent her to the bottom.

The following day some of her boats and hatch covers drifted ashore, along with a few hats. A few days later her sails were found adrift. It was a further nine months before six bodies were washed up 20 miles away.

That was the last that was heard of her for 228 years, until the discovery earlier this month by the marine archeologists Jim Kennard and Dan Scoville. Since they teamed up six years ago they have found seven ships in the lake.

The search for HMS Ontario began in earnest in 2005 after they obtained documents about the loss from British and Canadian archives. The search area covered more than 200 square miles of lake before they found the vessel.

Through the gloom of the sonic imagery they could see the ship sitting almost upright in 500ft of water, with its two masts stretching 70ft upwards. The remains of two crow’s nests helped to confirm it was the Ontario.

The two explorers have taken so many remote video images and photographs from their submersible before revealing their find that they believe the vessel need never be disturbed again and can be left as a war grave.

The shipwreck can be reached by only experienced divers, but Kennard, 64, and Scoville, 35, are keeping its precise location a secret.

Scoville said: “Usually when ships go down in storms, they get beat up quite a bit. They don’t sink nice and square. This went down in a huge storm and it still managed to stay intact.

“There are even two windows that aren’t broken. Just going down, the pressure difference can break the windows. It’s a beautiful ship.”

The depth of the waters has helped to preserve the vessel. The dark, cold freshwater acts as a perfect preservative. There is no light and no oxygen to hasten decomposition, and little marine life to feed on the wood.

A portion of the bowsprit remains and just below it there is a decoratively carved scroll bow stem. Two of the ship’s 22 cannon can be seen but they have come loose. Two of the large anchors are clearly visible. The explorers have also located the ship’s bell.

Arthur Britton Smith, who chronicled the history of the ship in his 1997 book The Legend of the Lake, has seen underwater video of the find. “To have a revolutionary war vessel that’s practically intact is unbelievable,” he said. “It’s an archaeological miracle.

“If it wasn’t for the zebra mussels, she looks like she only sunk last week.”

The Ontario was launched only five months before she sank. The British tried to keep her loss secret from George Washington’s troops because of the gap it left in their defences on the border with Canada.

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