On February 23, 1992, less than two months after the dissolution of the Soviet Union, I landed on the tarmac in Sarov, a city the government had removed from maps to keep secret its status as a nuclear weapons center. I was then director of the Los Alamos National Laboratory and­­ accompanied by two senior scientists from my own lab plus three colleagues from the Lawrence Livermore National Laboratory. The six of us were about to walk through the birthplace of the Soviet nuclear bomb, the technological and intellectual powerhouse behind the sophisticated arsenal that had been pointed at our country for the previous 40 years.

Shockingly, after an hour-long flight from Moscow, we stepped out of the Aeroflot turboprop into the open arms of our Russian hosts: Yuli Borisovich Khariton, the scientific leader of the Soviet nuclear program, and other senior lab staff who had waited in the chilly wind to welcome us. Just as remarkable was the fact that this wasn’t the first time we met our Russian counterparts. Two weeks earlier, directors of the Russian nuclear weapons labs, VNIIEF in Sarov and VNIITF in Snezhinsk, had for the first time in history set foot in our labs in Livermore and Los Alamos. This exchange of visits a quarter century ago marked a new turn in relations between the world’s two nuclear weapons superpowers.

The road to Sarov. Our first meeting on Russian soil would have been deemed improbable just a few months earlier. The encounter on the Sarov tarmac grew out of both persistence by determined individuals and larger historical forces. As the Soviet Union scrambled to adjust domestic and international policy in the face of mounting economic and social challenges in the late 1980s, Soviet leader Mikhail Gorbachev reached across the political divide to US President Ronald Reagan to take steps toward nuclear disarmament. One such step was the Joint Verification Experiment of 1988, in which the Soviet Union and the United States asked their nuclear weapons scientists to conduct parallel nuclear-explosion yield measurements at testing grounds in Nevada and Semipalatinsk, located in what is now Kazakhstan. The experiment helped overcome a stumbling block related to verification procedures needed to ratify the 1974 Threshold Test Ban Treaty (TTBT). The 1988 nuclear tests enabled the two sides to sign a new ratification protocol in Geneva in June 1990, and the TTBT entered into force in December 1990.

As history would have it, an unintended outcome of the TTBT ratification effort proved to be the most momentous. Viktor Mikhailov, head of the Soviet team that took part in the Joint Verification Experiment and later Russian minister of atomic energy, was right when he said that “the main result of the Joint Verification Experiment was not the development of procedures and extent of nuclear test monitoring of the joint development of technical verification means, but the chance for interpersonal communications with the American nuclear physicists.”

Indeed, it was working side by side at each other’s test sites that gave rise to deep-rooted affinity and built trust. Over the years, we had only caught glimpses of our Soviet nuclear scientist counterparts at a few international conferences where they disguised their institutional affiliations, saying they were part of the Soviet Academy of Sciences. It was through months of collaboration at our test sites that the contours of their true home institutions—the nuclear weapons labs VNIIEF and VNIITF—began to emerge. As we would discover eventually, these Soviet labs were remarkably similar to our own. We realized that in addition to nuclear weapons work, they were conducting outstanding fundamental science. We became consumed with curiosity to learn more about it first-hand. The Russians were curious about our work as well.

We were all interested in cooperation, but the Russians even more so because they sensed before we did just how dramatically the Soviet Union was changing. Lev D. Ryabev, who headed the atomic ministry at the time, told me years later that Russian nuclear weapons scientists were so eager to work with their American counterparts because “we arrived in the nuclear century all in one boat—movement by any one will affect everyone. We were doomed to work together.”

It was during a 1990 trip to Moscow by Los Alamos and Lawrence Livermore lab scientists for technical discussions supporting the Geneva test ban talks that Mikhailov extended an impromptu invitation to visit the USSR’s secret nuclear city Sarov (then called Arzamas-16) for the first time.

The American scientists returned with specific proposals from the VNIIEF director and his senior scientists for collaboration with the US labs, along with an invitation to Lawrence Livermore Director John Nuckolls and me to visit the secret Russian cities.

Convinced by my Los Alamos colleagues that this was a great opportunity to collaborate scientifically in important areas of research, I tried a number of avenues in Washington to get approval for exploring potential cooperation. I got little traction until the second half of 1991, after the Soviet Union had begun to disintegrate. As it did so, President George H.W. Bush became concerned that brain drain from the Soviet nuclear complex could lead to the spread of knowledge about how to build these weapons of mass destruction.

Driven by that concern, US Energy Secretary James D. Watkins approved my request for the laboratory directors’ exchange visits, and two months after Gorbachev’s formal dissolution of the Soviet Union on December 25, 1991, we entered the surreal world of the Soviet Los Alamos.

A tradition worth sustaining. Our visits to Sarov and Snezhinsk shattered our Cold War preconceptions of the Soviet nuclear program. We were particularly impressed by the depth of scientific talent. Although they lacked modern computers and electronics, their computational achievements were remarkable, and their experimental facilities were innovative and functional. We found the scientists’ dedication to their mission deeply patriotic, and their attention to nuclear weapons safety reassuring. During our briefings and tours, Russian scientists described leading-edge research in the fundamental science that underpinned their nuclear weapons program. The visits convinced me that our US nuclear labs should collaborate with their Russian counterparts, not only to help solve immediate problems like proliferation and loose nukes, but also because in doing so we would benefit scientifically.

Our Russian colleagues were prepared with proposals for cooperation in a surprisingly broad range of areas. During a daylong session in Chief Weapon Designer Boris Litvinov’s office in Snezhinsk, watched by portraits of Lenin and Igor Kurchatov, one of the fathers of the Soviet Bomb, we hammered out a protocol for cooperation that we would take back to our governments. We came up with a long list problems we wanted to work on together. It included enhancing the security and safety of nuclear weapons during reduction and dismantlement; preventing the proliferation of nuclear weapons knowledge; promoting the conversion and diversification of nuclear facilities; preventing non-nuclear states and terrorists from obtaining nuclear weapons; developing joint mechanisms for emergency response; enhancing the safety of nuclear arsenals; preventing unauthorized use of remaining weapons; and promoting protection and cleanup of the environment at nuclear weapons facilities.

It turned out that we scientists were far ahead of what the US government was prepared to authorize at the time. We heard that when members of the National Security Council staff, which coordinated interagency government issues with Russia, received a copy of the protocol, they declared it did not exist and threw it in the waste paper basket. However, Nuckolls and I presented the protocol to Watkins and received approval to proceed, though only in fundamental science cooperation.

By May 1992, even though the US Energy and State Departments had only agreed to general principles, the former had provided us with the necessary financial support and the latter with the required permissions for travel to Russia. Just as importantly, we had defined what we wanted to do first in the collaboration we called lab-to-lab. We planned for joint experiments in high-energy-density physics and conferences on computer modeling and simulation.

In spite of the initial US government concerns, we would eventually end up cooperating in almost all the areas outlined in the initial protocol. A spirit of collaboration prevailed for nearly a quarter century, and was essential to successfully mitigating the dangers resulting from the dissolution of the Soviet Union. Unfortunately, that cooperation has all but come to an end during the past few years as relations between Moscow and Washington have soured. But the benefits of future cooperation are potentially enormous, as a new report from the Nuclear Threat Initiative makes clear. The US and Russian governments, as well as the two countries’ scientists, should seize any opportunities that arise to rekindle nuclear cooperation.

Editor’s note: This column is based on materials in Doomed to Cooperate: How American and Russian Scientists Joined Forces to Avert Some of the Greatest Post-Cold War Nuclear Dangers, published by the Los Alamos Historical Society’s Bathtub Row Press in 2016.