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. Begun in the spring of 1964, before China had conducted its first bomb test, the “Nth Country Experiment” concluded that a government with nuclear-weapons aspirations and limited resources could develop a “credible” weapon.
This new Electronic Briefing Book includes the relatively limited declassified literature on the project, including the 1967 “Summary Report on the Nth Country Experiment,” a document first released to the National Security Archive in the 1990s and that was the subject of an Archive press release in 2003. Today’s posting also includes a recently declassified, if massively redacted, Livermore report on “Postshot Activities of the Nth Country Experiment” that summarized classified briefings that two of the participants in the Experiment gave around the country to U.S. government officials. Also included is a State Department internal announcement of a forthcoming briefing on the “Nth Country Experiment” noting that “three young PhD physicists, working part-time, succeeded in achieving a workable nuclear weapons design in a period of about three years.”
To begin the Experiment, Livermore Laboratory selected two recent PhDs, David N. Pipkorn (University of Illinois) and David A. Dobson (University of California, Berkeley). When Pipkorn left the Experiment for full-time work at Livermore, Robert W. Selden (University of Wisconsin) joined the project. The Experiment lasted longer than the one year envisaged, not concluding until the spring of 1967, when Dobson and Selden were ready to stage a hypothetical test for their design of a plutonium implosion weapon. During the months after the “test,” Dobson and Selden were on the road briefing staff at agencies and laboratories, including Los Alamos, the Central Intelligence Agency, the Atomic Energy Commission, and the State Department. The briefers made their presentation in the form of a nightly news report, Huntley-Brinkley style.
When the Experiment began in 1964, U.S. intelligence had been analyzing the problem of the potential spread of nuclear weapons capabilities for years. Before the term “nuclear proliferation” became widely used during the 1960s, however, analysts with the CIA and other intelligence organizations had thought in terms of a “4th country” problem: Which country was likely to join the U.S., the U.K., and the Soviet Union as the fourth country with nuclear weapons capabilities? After France tested its first bomb in early 1960 and became the fourth country, analysts began to think in terms of the “Nth country problem”—that some indeterminate number of countries might develop nuclear weapons capabilities. What concerned think tankers and academic experts was that Nth countries would create a more unstable and perilous world where the United States would have less influence and its interests would be under greater threat.[1] Consistent with this, during a 1963 press conference, President John F. Kennedy warned of the possibility of a world where, by the 1970s, there were 15 or 20 nuclear powers that posed the “greatest possible danger and hazard.”[2]
In the context of the early 1960s, some government officials and advisers might have wondered how difficult it would be for interested states to design effective nuclear weapons without access to classified information. More needs to be learned about the considerations and decisions that led officials at Livermore to sponsor the Nth Country Experiment, which they likely saw as a necessary and useful exercise in the broader context.
The Department of Energy’s reviewers massively excised the two reports on the Experiment on the grounds that they include “restricted data” (RD) relating to the design of nuclear weapons. The Experiment involved RD from the beginning, with the junior physicists involved receiving Q clearances; any nuclear weapons design information they created would, under the law, be considered secret and “born classified.” Thus, the DOE reviewers completely withheld all discussion and bibliographical entries related to the unclassified and open-source publications that the Experimenters consulted. In addition, the Energy Department excised the conclusions about the practicability of the design along with most details about it. Plainly, the Department of Energy’s reviewers did not want to release information that would increase anyone’s ability to develop nuclear weapons on their own. While access to fissile materials remains the most significant barrier to nuclear proliferation, it is difficult to find fault with the judgment that nuclear weapons design information deserves special protection.
With all the excisions, the reports nevertheless convey some details about the Experiment and how it proceeded. One hint about the kind of unclassified literature available they relied on is found in a discussion about the advantages that the Experimenters had over the “outstanding” and highly motivated physicists who worked at Los Alamos during World War II, who were not even sure whether a nuclear weapon could be produced. By contrast, 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.”
The declassified text of the “Summary Report” also indicated that the Experimenters decided to design a plutonium implosion device instead of the highly enriched uranium device that detonated over Hiroshima. Although the latter would have taken less time to develop, the Experimenters believed that, for an Nth Country, the plutonium weapon would have “greater potential for future development and more efficiency because the 1945 implosion bombs gave greater yields.” By the close of 1965, they had prepared “an historically accurate description of our first complete plutonium implosion design.” In April 1967, after three years of effort, their implosion design had a “hypothetical test.” The Experimenters believed that their design was realistic enough that it would not require an explosive test compared to developing thermonuclear weapons. As they wrote, “from our present understanding of nuclear explosives, our Final Design is credible without a test, but we see no way to design a credible thermonuclear explosive without testing.”
Decades after the experiment, two journalists, Dan Stober and Oliver Burkman, interviewed Dobson and Selden about their experience, their working relationship, and the results of the Nth Country experiment.[3] Dobson and Selden told them about some of the open sources they had consulted for clues on weapons design, such as a 1960 National Planning Association report[4] but also of the extensive literature on explosives and various unclassified reports in the Livermore Library.
By the end of 1965, they had a rough design for a plutonium implosion weapon, and, later in 1966, “their design was final.” Apparently, their report had enough engineering detail that a “Machine Shop could have fabricated the device.” While the weapon was “too big to fit on a missile, [it was] small enough to be carried by airplane or truck.”
Dobson and Selden did not learn whether their design could work until after they had given their final briefing at Livermore. According to Dobson, James Frank told them, “that if it had been constructed, it would have made a pretty impressive bang.” It would have been “on the same order of magnitude as Hiroshima.”
Dobson left nuclear weapons work for a career in teaching physics at Beloit College. Selden made a career in weapons development work at Livermore and Los Alamos, eventually becoming the U.S. Air Force’s chief scientist. Both remained concerned about the implications of their “do it yourself” project for prospects for nuclear terrorism in a post-9/11 world. According to Selden, “the key question of the time we live in” is whether a terrorist group could develop a nuclear weapon, whether using reactor-grade plutonium or highly enriched uranium: “It’s certainly possible for a terrorist group if they’re really technically savvy and have a lot of resources.”[5] Having participated in the Nth Country Experiment, Selden knew well what he was talking about.
Future declassifications by the Department of Energy may lead to the release of more information about the “Nth Country Experiment” and its inception. The National Security Archive has appealed the excisions from the “Postshot” report on the grounds that the Energy Department may have withheld information that it had previously declassified from the 1967 “Summary Report.”
Notes
[1]. See, for example, Fred Iklé, Hans Speier, Bernard Brodie, Alexander George, Alice Hseih, and Arnold Kramish, The Diffusion of Nuclear Weapons to Additional Countries: The “Nth Country” Problem, RAND Research Memorandum 2484-RC, 15 February 1960, and National Planning Association, The Nth Country Problem and Arms Control: A Statement by the NPA Special Committee on Security Through Arms Control and a Technical Report by W. Davidon, M. Kalkstein, and C. Hohenemser (Washington, D.C.: National Planning Association, 1960)
[2]. Press Conference, 21 March 1963, Public Papers of the President John F. Kennedy, 1963 (Washington, D.C., Government Printing Office, 1964), 280
[3]. Dan Stober, “No Experience Necessary,” The Bulletin of the Atomic Scientists 59 (2003): 57-63; Oliver Burkeman, “How Two Students Built an A-Bomb,” Guardian, 24 June 2003.
[4]. See National Planning Association report cited in endnote 1.
[5]. Stober, “No Experience Necessary,” 62.
[6]. For the development of the initiator in the early implosion weapon, see Lillian Hoddeson et al., Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943-1945 (New York: Cambridge University Press, 1993) 308-310 and 316-319. For Neils Bohr’s contribution to the debate at Los Alamos over initiator design, see Alex Wellerstein, “Bohr at Los Alamos.”
[7]. The classic exposition is Donald MacKenzie and Graham Spinardi’s, “Tacit Knowledge, Weapons Design, and the Uninvention of Nuclear Weapons,” American Journal of Sociology,101 (1995), 44-99.
