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Nuclear Proliferation and the "Nth Country Experiment"

Washington, D.C., January 23, 2025 - Today, the National Security Archive publishes newly declassified information on a secret mid-1960s project in which a handful of young physicists at Lawrence Livermore Laboratory produced a design for a “credible nuclear weapon” based only on unclassified, open-source information and in just three years. One of the participants described the experiment as “truly a do-it-yourself project,” according to one of the recently declassified records.

Looking back at the Los Alamos lab during World War II, they noted that the people there “had advantages of manpower and experience (including the presence of some of the world’s outstanding physicists) and the motivational climate in which they worked.” Yet the Experimenters had “the advantages of knowing that a bomb could be built and of having access to a large quantity of literature on shock waves, explosives, nuclear physics and reactor technology which has been published since 1945.” An interesting section in the report [Appendix D] includes discussion of what Dobson and his colleagues knew about nuclear weapons prior to the Experiment, but also what they found to be “possible security leak[s]” both at the lab and in the open literature, although the security reviewers redacted the substance of both. Fulton’s brief description of the Experiment characterized it as a success: Using no classified information but having access to LRL computers for making calculations, “three young PhD physicists, working part-time, succeeded in achieving a workable nuclear weapons design in a period of about three years.” Lasting until the summer of 1968, the Nth Country Experiment road show began with briefings to LRL and the Rand Corporation and continued with presentations to organizations in the Washington, D.C., area, including the JAEC, the CIA, various AEC offices, the Defense Atomic Support Agency, and the U.S. Intelligence Board.

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