PARIS Britain in the 1950s made gigantic nuclear bombs, each the equivalent of 25 Hiroshima blasts, that its air force feared could explode by accident, the British weekly ***New Scientist***** reports in next Saturday's issue.

Up to a dozen weapons were made of a type codenamed Violet Club, each holding around 70 kilos (154 pounds) of uranium 235, enough to create a 500-kiloton explosion, it said, citing recently declassified Royal Air Force (RAF) documents.

The RAF was worried that when the bombs' safety mechanism was disabled there was a "risk of a catastrophe," according to these documents.

In one memo dated January 12 1959, an officer identified as group Captain Tait wrote: "A high-yield nuclear explosion would be possible if the weapon were jettisoned, or in the event of a crash on return, or an accident in debombing."

The safety mechanism amounted to 450 kilos (990 pounds) of steel balls.

These were packed into sections of the bomb, separating the uranium so that it would not reach critical mass.

Violet Club, designed to be dropped by the now-decommissioned Vulcan long-range bomber, also took too long to arm, ****New Scentist**** adds.

The RAF was tasked with being able to launch a nuclear-armed aircraft within 15 minutes -- but it took at least 20 minutes to remove the metal balls and arm one of these bombs.

Lesley wright, an academic from John Moores University in Liverpool, who was one of a team that unearthed the documents in the Public Records Office, said the bombs had been forced on the RAF by a government that was eager to follow the United States and Soviet Union in making megaton-range bombs.

"This is a prime example of how the pursuit of superpower status and fear overcame rational decision-making," she said.

The British Defense Ministry told ****New Scientist*** there had been "no risk" of an accidental detonation of a Violet Club.

"All the necessary precautions" were taken to ensure the device was "transported and stored safely," a spokesman said.