Approved at the highest levels of the Army in 1948, the effort was a well-hidden part of the military's pursuit of a "new concept of warfare" using radioactive materials from atomic bombmaking to contaminate swaths of enemy land or to target military bases, factories or troop formations.
Military historians who have researched the broader radiological warfare program said in interviews that they had never before seen evidence that it included pursuit of an assassination weapon. Targeting public figures in such attacks is not unheard of; just last year an unknown assailant used a tiny amount of radioactive polonium-210 to kill Kremlin critic Alexander Litvinenko in London.
No targeted individuals are mentioned in references to the assassination weapon in the government documents declassified in response to a Freedom of Information Act request filed by the AP in 1995.
The decades-old records were released recently to the AP, heavily censored by the government to remove specifics about radiological warfare agents and other details. The censorship reflects concern that the potential for using radioactive poisons as a weapon is more than a historic footnote; it is believed to be sought by present-day terrorists bent on attacking U.S. targets.
The documents give no indication whether a radiological weapon for targeting high-ranking individuals was ever used or even developed by the United States. They leave unclear how far the Army project went. One memo from December 1948 outlined the project and another memo that month indicated it was under way. The main sections of several subsequent progress reports in 1949 were removed by censors before release to the AP.
The broader effort on offensive uses of radiological warfare apparently died by about 1954, at least in part because of the Defense Department's conviction that nuclear weapons were a better bet.
Whether the work migrated to another agency such as the CIA is unclear. The project was given final approval in November 1948 and began the following month, just one year after the CIA's creation in 1947.
It was a turbulent time on the international scene. In August 1949, the Soviet Union successfully tested its first atomic bomb, and two months later Mao Zedong's communists triumphed in China's civil war.
As U.S. scientists developed the atomic bomb during World War II, it was recognized that radioactive agents used or created in the manufacturing process had lethal potential. The government's first public report on the bomb project, published in 1945, noted that radioactive fission products from a uranium-fueled reactor could be extracted and used "like a particularly vicious form of poison gas."
Among the documents released to the AP - an Army memo dated Dec. 16, 1948, and labeled secret - described a crash program to develop a variety of military uses for radioactive materials. Work on a "subversive weapon for attack of individuals or small groups" was listed as a secondary priority, to be confined to feasibility studies and experiments.
The top priorities listed were:
The stated goal was to produce a prototype for the No. 1 and No. 2 priority weapons by Dec. 31, 1950.
The 4th ranked priority was "munitions for attack on individuals" using radioactive agents for which there is "no means of therapy."
"This class of munitions is proposed for use by secret agents or subversive units for lethal attacks against small groups of important individuals, e.g., during meetings of civilian or military leaders," it said.