A MAN who went diving for sea cucumbers got more than he bargained for when he swam straight into a missing nuclear bomb.

But so unexpected was Sean Smyrichinsky’s find, off the western coast of Canada, that he initially thought it was a UFO.

Now the Canadian Navy has been dispatched to see if the diver’s explosive claims stack up and he really has found an arrant atomic bomb.

If proved right, Mr Smyrichinsky may have inadvertently solved one of the biggest mysteries of the Cold War — what happened to a nuclear bomb jettisoned by a US aircraft in 1950 just before it crashed.

Mr Smyrichinsky claimed he recently went diving in a remote area close to Pitt Island, off the coast of British Columbia, using an underwater scooter.

Scouring the sea bed for sea cucumbers one last time, he stumbled across something he couldn’t explain.

“I found this big thing underwater, huge, never seen anything like it before,” Mr Smyrichinsky told the Vancouver Sun.

“I came up telling all my buddies on the boat ‘Hey, I found a UFO. It’s really bizarre.’ And I drew a picture of it, because I didn’t have a camera.”

Talking to the BBC, Mr Smyrichinsky described it as, “bigger than a kingsize bed”, perfectly flat on top with a rounded bottom and had a hole in the centre just “like a bagel.”

He told a few stumped fisherman before one of them said, ‘Oh, you might have found that bomb.’”

That bomb was an 11,000 pound (4900kg) Mark IV “Fat Man” American nuclear weapon at least as large as those that were dropped on Hiroshima and Nagasaki in the dying days of the Second World War.

One of 500 produced in the 1940s, it was the first ever “broken arrow” incident, or accident involving an atomic weapon.

In February 1950, an American military plane, a Convair B-36B bomber, took off from Eilson air base in Alaska headed for its home base of Carswell near Dallas, Texas.

The plane was on a simulated nuclear strike mission and carried a bomb to test how effectively it could fly with such a heavy payload.

Flying along the Canadian coast, several of the plane’s engines iced up and shut down. Unable to stay aloft, the crew parachuted from the aircraft, five of them killed in the process after its suspected they landed in the freezing ocean.

The US military have always said the Fat Man device was not armed.

Nevertheless, the crew were so concerned about the combination of TNT, lead and uranium the device did contain, they offloaded the bomb into the sea rather than have it explode on land.

Desperate for the Soviets not to get their hands on sensitive military material, the US authorities immediately began a search for the plane, and it’s payload, thinking it had ditched in the sea.

It would take three years before the Convair was found deep inland, smashed into the side of the mountain.

Fragments of the bomb were never found, perhaps until now.

Mr Smyrichinsky said the object he found was “a big bowl, at least 12 feet across, maybe bigger.”

“The bowls (inside the main bowl) are much larger than basketballs, maybe 24 inches across. They’re very smooth on the inside and they’re all around the centre of this thing.”

While the weapon isn’t intact, from researching the design of the bomb, Mr Smyrichinsky believes he may have found the section of the nuke that held the explosive material.

Major Steve Neta of the Canadian Armed Forces confirmed to Canadian broadcaster CBC Mr Smyrichinsky s find could be well be linked to the 1950 broken arrow.

“We do want to be sure and we do want to investigate it further,” he said.

The Royal Canadian Navy ship deployed to investigate should arrive in the area in the next few weeks.

Time, it seems, has mellowed the anxiety of the Americans. Even if it is one of their bombs that has been found, they are so convinced it’s inert and its technology is obsolete, they seem happy for their northern neighbours to take possession of it.