Nuclear arms race

• 1. Introduction

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  The nuclear arms race began not with a treaty or a speech, but with 187 liters of heavy water smuggled out of Norway ahead of a German invasion. That single cargo -- secured by a French intelligence agent in early 1940, routed through Paris and then England, and ultimately stored at the Cavendish Laboratory in Cambridge -- sat at the heart of a global contest that would eventually place tens of thousands of warheads on hair-trigger alert. How did two wartime allies become the architects of a rivalry capable of killing 5 billion people by starvation alone, according to a peer-reviewed study published in the journal Nature Food in 2022? How did a competition rooted in a single European hydroelectric plant become a permanent feature of international life, outlasting the Cold War that spawned it? And what happens when the treaties designed to keep that competition in check begin to collapse, one by one?

• 2. Sabotage and Spies

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  Norsk Hydro's Vemork plant in Rjukan was, from 1934, the only facility in the world producing heavy water at industrial scale. Both the French and the Germans wanted it. The French moved faster, persuading the Norwegian government by disclosing the military purpose of the purchase, while the Germans got a refusal. That heavy water traveled an improbable route -- Paris, England, and finally Cambridge -- before arriving in the hands of refugee French physicists Hans von Halban and Lew Kowarski.

  In February 1941, the Luftwaffe attacked Cambridge. Kowarski said after the war that the strike on the Cavendish Laboratory was deliberate retaliation for a British raid on Heidelberg, where Walther Bothe and Arnold Flammersfeld were running parallel atomic pile experiments at the institution now known as the Max Planck Institute for Medical Research.

  The sabotage campaign against the German program reached its most decisive moment in February 1943, when a Special Operations Executive-trained team of Norwegian commandos detonated charges on the heavy-water electrolysis chambers at Vemork during Operation Gunnerside. That action, combined with subsequent bombing raids, crippled German moderator production for the remainder of the war.

  Behind the Allied lines, the intelligence effort grew personal. In December 1944, OSS spy Moe Berg traveled to Zurich where Werner Heisenberg was delivering a lecture. Berg carried a concealed pistol and orders to shoot Heisenberg if he judged the German bomb program to be near completion. Berg did not fire. When the Western Allies captured the Haigerloch nuclear pile in April 1945, they confirmed what Berg may have sensed: the German program was comparatively limited. Most of the leading German scientists, including Heisenberg and Paul Harteck, were taken by Western Allied forces between May and June in an operation called Epsilon.

• 3. The Soviet Acceleration

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  Stalin was briefed on the Manhattan Project by U.S. President Harry Truman at the Potsdam Conference on the 24th of July 1945 -- eight days after the first successful nuclear test. Truman later recalled that Stalin reacted with surprising calm, and the American and British delegations observing the exchange concluded that Stalin had not understood what he had been told. Stalin, in fact, had known about the program for years. A ring of spies inside the Manhattan Project, including Klaus Fuchs and Theodore Hall, had kept him informed of American progress and provided detailed designs of both the implosion bomb and the hydrogen bomb.

  Fuchs' arrest in 1950 unraveled much of that network. It led to the arrest of Harry Gold, David Greenglass, and Ethel and Julius Rosenberg, who were tried and executed for espionage in 1951.

  American experts had predicted the Soviet Union would not detonate a nuclear device until the mid-1950s. The first Soviet bomb exploded on the 29th of August 1949 -- a device the West called "First Lightning" and which was, in design, a near-copy of the "Fat Man" bomb dropped on Nagasaki. The gap had closed years ahead of schedule.

  The race into hydrogen weapons was equally compressed. The United States detonated the first hydrogen bomb on the 1st of November 1952, on the Pacific atoll of Enewetak. Code-named "Ivy Mike" and led by Edward Teller, it created a cloud 100 miles wide and 25 miles high, and killed all life on the surrounding islands. Less than a year later, in August 1953, the Soviets detonated a deployable thermonuclear device -- not a true multi-stage hydrogen bomb, but compact enough to be dropped from an aircraft. The Soviet Union detonated its first true hydrogen bomb on the 22nd of November 1955, with a yield of 1.6 megatons. On the 30th of October 1961, that program culminated in the Tsar Bomba, a device with a yield of approximately 58 megatons.

• 4. The Triad and the Gap

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  Strategic bombers were the only delivery method at the start of the Cold War, but the logic of nuclear deterrence demanded more options. Beginning in the 1950s, both sides developed medium- and intermediate-range ballistic missiles, then pushed that technology toward intercontinental range. On the 4th of October 1957, the Soviet Union launched Sputnik 1, the first artificial satellite to orbit the Earth, which simultaneously demonstrated that Soviet ICBMs could reach any point on the planet. The United States launched its first satellite, Explorer 1, on the 31st of January 1958.

  By the mid-1960s, the nuclear triad was established: each side deployed bombers, intercontinental ballistic missiles, and submarine-launched ballistic missiles. The logic was redundancy -- if a defense neutralized one delivery method, the others would still guarantee a retaliatory strike.

  Not everyone was convinced the system was reliable. Some American critics pointed out that individual components of nuclear missiles had been tested separately but never as an integrated system. The closest test of a complete ICBM-equivalent occurred in 1962's Operation Frigate Bird, in which a submarine launched a Polaris A2 missile more than 1,000 miles to the nuclear test site at Christmas Island. Critics noted it was a single data point, conducted at lower altitude than an ICBM flight path, and that significant modifications had been made to the warhead before testing.

  The perception of gaps drove policy as much as actual capability. In the 1950s, American planners believed in a bomber gap -- a non-existent Soviet advantage. Aerial photography later revealed the Soviets had been flying their bombers in large circles during military parades to create the illusion of a far larger fleet. The 1960 presidential election was shaped partly by accusations of a missile gap that also turned out to be spurious. Meanwhile, Soviet first secretary Nikita Khrushchev was receiving exaggerated figures about Soviet weapons from his own military leadership.

• 5. The Cuban Edge

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  On the 1st of January 1959, Fidel Castro came to power in Cuba. The Soviet Union recognized his government nine days later. When the United States began boycotting Cuban sugar, the Soviet Union stepped in as a buyer and gradually deepened its commitment, eventually placing nuclear ballistic missiles on the island. On the 14th of October 1962, an American spy plane photographed those missile sites under construction.

  President Kennedy ordered a naval blockade around Cuba and raised American forces to DEFCON 3, then ultimately DEFCON 2 -- the highest alert level reached during the entire Cold War. On October 26, Khrushchev wrote to Kennedy in a telegram warning that if both sides did not relax their grip on the rope, the world would be "doomed to the catastrophe of thermonuclear war".

  On October 28, Khrushchev announced the Soviet missiles would be withdrawn from Cuba. What the world did not know for decades was that the United States had simultaneously agreed to remove its Jupiter missiles from Turkey -- a concession kept confidential by both sides. The public version of events appeared to be an unambiguous American victory. That perception contributed directly to Khrushchev's political downfall.

  The crisis exposed how completely each side lacked reliable information about the other's capabilities and intentions. It also demonstrated that the doctrine of mutual assured destruction -- both sides would be devastated by any exchange -- operated as a genuine restraint. The crisis produced no nuclear exchange not because of treaty obligations but because both leaders ultimately chose the diplomatic track, even as their own governments were positioned for war.

• 6. Treaties and Their Limits

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  On the 10th of October 1963, the United States, the Soviet Union, and the United Kingdom signed the Limited Test Ban Treaty, prohibiting nuclear tests in the atmosphere, underwater, and in outer space. Underground testing was still permitted. An additional 113 countries eventually signed the treaty.

  Strategic Arms Limitation Talks began in November 1969, driven in large part by the economic toll that nuclear production was inflicting on both superpowers. The SALT I Treaty, signed in May 1972, produced two key documents: the Anti-Ballistic Missile Treaty, which limited each country to two ABM sites, and the Interim Agreement, which froze intercontinental and submarine-launched ballistic missile numbers at current levels for five years. What SALT I failed to address was how many warheads a single missile could carry. A technology called MIRV -- multiple independently targetable re-entry vehicle -- allowed one missile to carry and release several warheads aimed at different targets. Over the decade that followed, the two countries added roughly 12,000 nuclear warheads to their existing arsenals.

  The SALT II treaty was signed in Vienna on the 18th of June 1979. The United States Senate never ratified it, partly because the Soviet Union invaded Afghanistan in December 1979. Détente effectively ended.

  On the 8th of August 1974, in the midst of the negotiations, the CIA's Project Azorian recovered Soviet nuclear torpedoes from the wreck of the sunken submarine K-129. The raising ship Glomar Explorer lost the section of the submarine containing the R-13 ballistic missiles and nuclear warheads, as well as codebooks and decoding machines. The recovery mission's full scope and what was actually retrieved remained classified for years.

• 7. Collapse and Continuation

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  Mikhail Gorbachev assumed leadership of the Soviet Union after the deaths of several predecessors and announced a new era of "perestroika" (restructuring) and "glasnost" (openness). At a meeting in Reykjavik, Iceland, in October 1986, he proposed cutting nuclear weapons by 50% for both sides. Reagan refused, unwilling to abandon the Strategic Defense Initiative -- a space-based missile defense system critics called "Star Wars," which proposed laser battle stations in orbit and sensor networks across the ground, air, and space. Owing to the costs and complexity involved, the SDI was eventually scaled back from defending against a full-scale attack to defending against limited strikes.

  The Intermediate Nuclear Forces Treaty was signed on the 8th of December 1987, in Washington, eliminating an entire class of nuclear weapons. The START treaty, negotiated in July 1991, reduced strategic offensive arms. By the 25th of December 1991, Gorbachev had resigned as Soviet president, and the following day the Soviet Union was declared non-existent.

  In 2015, the Federation of American Scientists estimated that 125,000 nuclear weapons had been produced between 1945 and 2013. The environmental legacy of that production remained. In the United States, the plutonium production facility at Hanford, Washington, and the plutonium pit fabrication facility at Rocky Flats, Colorado, ranked among the most contaminated sites in the country.

  The collapse of the Soviet Union did not end the competition. On the 13th of December 2001, George W. Bush gave Russia notice of American withdrawal from the Anti-Ballistic Missile Treaty. Vladimir Putin responded by ordering a build-up of Russian nuclear capabilities. The INF Treaty and New START both broke down in 2019 and 2023, against the backdrop of the war in Ukraine. A peer-reviewed study in the journal Nature Food in August 2022 calculated that a full-scale nuclear exchange between the United States and Russia, together holding more than 90% of the world's nuclear weapons, would kill 360 million people directly and more than 5 billion indirectly through starvation during a nuclear winter -- roughly 99% of the populations of the US, Europe, Russia, and China. In July 2024, the Biden administration announced plans to deploy long-range missiles in Germany starting in 2026, capable of reaching Russian territory within 10 minutes.