U.S. worked on secret Cold War weapon

Radioactive agents were thought to be ideal for this use, the document said, because of their high toxicity and the fact that the targeted individuals could not smell, taste or otherwise sense the attack.

"It should be possible, for example, to develop a very small munition which could function unnoticeably and which would set up an invisible, yet highly lethal concentration in a room, with the effects noticeable only well after the time of attack," it said.

"The time for lethal effects could, it is believed, be controlled within limits by the amount of radioactive agent dispersed. The toxicities are such that should relatively high concentrations be required for early lethal effects, on a weight basis, even such concentrations may be found practicable."

Tom Bielefeld, a Harvard physicist who has studied radiological weapons issues, said that while he had never heard of this project, its technical aims sounded feasible.

Bielefeld noted that polonium, the radioactive agent used to kill Litvinenko in November 2006, has just the kind of features that would be suitable for the lethal mission described in the Dec. 16 memo.

Barton Bernstein, a Stanford history professor who has done extensive research on the U.S. military's radiological warfare efforts, said he did not believe this aspect had previously come to light.

"This is one of those items that surprises us but should not shock us, because in the Cold War all kinds of ways of killing people, in all kinds of manners — inhumane, barbaric and even worse — were periodically contemplated at high levels in the American government in what was seen as a just war against a hated and hateful enemy," Bernstein said.

Army Chemical Corps ran it
The project was run by the Army Chemical Corps, commanded by Maj. Gen. Alden H. Waitt, and supervised by a now-defunct agency called the Armed Forces Special Weapons Project. The project's first chief was Maj. Gen. Leslie R. Groves, the Army's head of the Manhattan Project that built the first atomic bombs. The radiological project was approved by Groves' successor, Maj. Gen. Kenneth D. Nichols.

The released documents were in files of the Armed Forces Special Weapons Project held by the National Archives.

Among the officials copied in on the Dec. 16 memo were Herbert Scoville, Jr., then the technical director of the Armed Forces Special Weapons Project and later the CIA's deputy director for research, and Samuel T. Cohen, a physicist with RAND Corp. who had worked on the Manhattan Project.

The initial go-ahead for the Army to pursue its radiological weapons project was given in May 1948, a point in U.S. history, following the successful use of two atomic bombs against Japan to end World War II, when the military was eager to explore the implications of atomic science for the future of warfare.

In a July 1948 memo outlining the program's intent, before specifics had received final approval, a key focus was on long-lasting contamination of large land areas where residents would be told that unless the areas were abandoned they probably would die from radiation within one to 10 years.

"It is thought that this is a new concept of warfare, with results that cannot be predicted," it said.

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