LONDON — A claim that Britain considered using live chickens in a nuclear weapon aroused skepticism Thursday, but officials insisted it was not an April Fool's hoax.

"It's a genuine story," said Robert Smith, head of press and publicity at The National Archives. The archives released a secret 1957 Ministry of Defence report showing that scientists contemplated putting chickens in the casing of a plutonium landmine.

The chickens' body heat was considered a possible means of preventing the mine's mechanism from freezing.

Listing ways of extending the armed life of the landmine, the declassified document proposed "incorporating some form of heating independent of power supplies under the weapon hull in the emplacement. Chickens, with a heat output of the order of 1,000 BTU (British Thermal Units) per bird per day are a possibility."

The seven-tonne device, code named Blue Peacock, would have been detonated from a distance or by timer in the event of a retreat from invading Soviet troops, to prevent them from occupying the area.

Andy Oppenheimer, co-editor of Jane's World Armies, said he found the idea of using chickens hard to believe.

"I have a feeling that it's an April Fool," he said in a phone interview. He said wrapping the device in fibreglass to keep it warm would have been a better option.

Some newspapers also expressed skepticism.

"Is today the day to reveal the chicken-powered nuke?" The Times of London wrote, referring to the April 1 date. Nonetheless, The Times put it on page one.

Tom O'Leary, head of education and interpretation at the National Archives, said he had no doubt that the document was authentic.

"None whatsoever," he said in a telephone interview with The Associated Press. "It's not the kind of thing the civil service does, to set up an April Fool's joke."

O'Leary said the idea is mentioned briefly in a long document.

"It's purely a suggestion in an official document that that is a possibility that was proposed," he said, and there was no indication that the feasibility was ever tested.

The Blue Peacock project began in 1954 and was aimed at preventing enemy occupation of territory due to nuclear contamination. Designs were based on Britain's Blue Danube free-fall bomb, which consisted of a plutonium core surrounded by a sphere of high explosive with detonators spread across the surface.

Officials decided in 1957 to acquire 10 Blue Peacock landmines, each weighing 7,250 kilograms, and to station them with the British Army of the Rhine in Germany. However, in 1958 the Ministry of Defence Weapons Policy Committee decided that work on Blue Peacock should stop, after reservations emerged about the fallout hazard.

A prototype survives in the historical collection of the Atomic Weapons Establishment, a government agency which has its headquarters at Aldermaston west of London.

"The whole operational scenario appeared somewhat theatrical," said an article in the AWE's magazine in January. It did not mention chickens, but did deal with the problem of maintaining the right temperature.

"The nuclear warhead had to be kept within a specific temperature range, but environmental trials suggested it might not have survived the rigours of a mid-European winter," the article said.

Details of the chicken proposal feature in an April 2-Oct. 30 exhibition entitled The Secret State at the National Archives in Kew, west London.