Nuclear arms race
The nuclear arms race was an arms race competition for supremacy in nuclear warfare between the United States, the Soviet Union, and their respective allies during the Cold War. During this same period, in addition to the American and Soviet nuclear stockpiles, other countries developed nuclear weapons, though no other country engaged in warhead production on nearly the same scale as the two superpowers.
The race began during World War II, dominated by the Western Allies' Manhattan Project and Soviet atomic spies. Following the atomic bombings of Hiroshima and Nagasaki, the Soviet Union accelerated its atomic bomb project, resulting in the RDS-1 test in 1949. Both sides then pursued an all-out effort, realizing deployable thermonuclear weapons by the mid-1950s. The arms race in nuclear testing culminated with the 1961 Tsar Bomba. Atmospheric testing was ended in the 1963 Partial Nuclear Test Ban Treaty. Subsequent work focused on the miniaturization of warheads at LLNL and VNIITF, and the neutron bomb.
Seven other countries developed nuclear weapons during the Cold War. The UK and France, both NATO members, developed fission and fusion weapons throughout the 1950s, and 1960s, respectively. China developed both against the backdrop of the Sino-Soviet split. Israel, India, Pakistan, and South Africa subsequently developed at least fission weapons.
Nuclear weapons delivery vehicles were a major field of competition. Initially strategic bombers were the only option. By 1960, both sides had developed intercontinental ballistic missiles and submarine-launched ballistic missiles, resulting in the nuclear triad. Additionally, smaller systems for tactical nuclear weapons delivery were extensively developed and deployed. Key regions of nuclear build-up included the Eastern European Warsaw Pact, NATO members West Germany, Italy, Greece, and Turkey, and US-allied Japan, South Korea, Taiwan, and the Philippines.
Confrontations with nuclear threats occurred during the Korean War, the First and Second Taiwan Strait Crises, the Berlin Crisis of 1961, and most significantly the Cuban Missile Crisis. Détente during the 1960s and 1970s limited the arms race, especially via the Non-Proliferation Treaty and Anti-Ballistic Missile Treaty. Tensions were renewed in the early 1980s, in the development and deployment to Europe of MRBMs, IRBMs, and supersonic strategic bombers, as well as the space-based Strategic Defense Initiative. Under the leadership of Mikhail Gorbachev, the USSR negotiated the Intermediate-Range Nuclear Forces Treaty and START I, until its dissolution in 1991 brought to an end the Cold War nuclear arms race.
Russia and the US maintain the world's largest nuclear stockpiles. The 1993 START II, 1996 CTBT, and 2010 New START treaties further curtailed the arms race in the post-Cold War period. Tensions have resurged in what is sometimes called a Second Cold War. The US-Russian INF and New START treaties broke down in 2019 and 2023, against the backdrop of the Russia-Ukraine War, and Russia announced six "nuclear super weapons". In the Pacific, the US and China are in competition over hypersonic weapons.
World War II
During World War II, four nuclear weapons research programs existed. The industrial Manhattan Project, directed by the US military and coordinated with the UK and Canada, developed the first nuclear weapons. More limited scientific research was carried out in the Soviet atomic bomb project, German nuclear program, and Japanese nuclear program.Allied-German rivalry
From 1934, the Vemork hydroelectric station of Norsk Hydro Rjukan entered operation as the world's only industrial-scale production site for heavy water, suitable as a moderator for atomic pile experiments leading to nuclear reactors.In early 1940, a French Deuxième Bureau agent arranged for the purchase of the entire Norwegian stock of heavy water, 187 liters. The Germans had offered the same purchase, but the French obtained the agreement of the Norwegian government after telling them of its military purpose. It was shipped to the Collège de France nuclear laboratory in Paris prior to the German invasion of Norway in April, but during the German invasion of France in June it was shipped to England. After various secret storages it was moved to the Cavendish Laboratory in Cambridge, for the work of refugee French nuclear physicists Hans von Halban and Lew Kowarski.
In February 1941, the Luftwaffe carried out a raid on Cambridge, hitting the Cavendish Laboratory. Kowarski said in a postwar interview that his and von Halban's work there on a heavy water-moderated atomic pile was specifically targeted in retaliation for a prior British raid on Heidelberg, where Walther Bothe and Arnold Flammersfeld were working on similar pile experiments at what is now the Max Planck Institute for Medical Research.
In February 1943, a Special Operations Executive-trained team of Norwegian commandos detonated explosive charges on the heavy-water electrolysis chambers at the Vemork hydroelectric plant during Operation Gunnerside. Along with other covert and bombing raids, the Allies successfully crippled heavy water moderator production for the German nuclear program.
In 1943, a US Office of Strategic Services operation named Project AZUSA aimed to interview Italian physicists to learn what they knew about German nuclear physicists Werner Heisenberg and Carl Friedrich von Weizsäcker. In December 1944, OSS spy Moe Berg travelled to Zurich where Heisenberg was giving a lecture, with orders to shoot Heisenberg with a concealed pistol if he deemed the German atomic bomb program close to completion.
US-Soviet rivalry
In the first half of 1945, as the Western theater was coming to a close, the US and Soviets competed over the intellectual and material resources of the German nuclear program, via the Alsos Mission and Russian Alsos. In March, Manhattan Project leader Leslie Groves ordered the Auergesellschaft plant in Oranienburg bombed, to deny the Soviets the refined natural uranium there. Nonetheless 100 tons were ultimately recovered and used for their early reactors. In April, the Western Allies captured the Haigerloch nuclear pile, showing the comparative limited nature of the German program. The majority of leading German scientists, including Werner Heisenberg and Paul Harteck, were captured by the Western Allies between May and June in Operation Epsilon. Alsos interrogated Fritz Houtermans, a German who had worked on nuclear research for Germany and the USSR, about the extent of the Soviet project. The Soviets captured Nikolaus Riehl, Gernot Zippe, and Max Steenbeck, of which the latter two were later crucial in developing the uranium hexafluoride gas centrifuge. During the occupation of Japan, Alsos also interrogated nuclear physicists, but found their work was limited to unsuccessful enrichment experiments.The Soviet Union was not informed officially of the Manhattan Project until Stalin was briefed at the Potsdam Conference on July 24, 1945, by U.S. President Harry S. Truman, eight days after the first successful test of a nuclear weapon. Despite their wartime military alliance, the United States and Britain had not trusted the Soviets enough to keep knowledge of the Manhattan Project safe from German spies; there were also concerns that, as an ally, the Soviet Union would request and expect to receive technical details of the new weapon.
When President Truman informed Stalin of the weapons, he was surprised at how calmly Stalin reacted to the news and thought that Stalin had not understood what he had been told. Other members of the United States and British delegations who closely observed the exchange formed the same conclusion.
In fact, Stalin had long been aware of the program, despite the Manhattan Project's having a secret classification so high that, even as vice president, Truman did not know about it or the development of the weapons. A ring of spies operating within the Manhattan Project, had kept Stalin well informed of American progress. They provided the Soviets with detailed designs of the implosion bomb and the hydrogen bomb. Fuchs' arrest in 1950 led to the arrests of many other suspected Russian spies, including Harry Gold, David Greenglass, and Ethel and Julius Rosenberg; the latter two were tried and executed for espionage in 1951.
In August 1945, on Truman's orders, two atomic bombs were dropped on Japanese cities. The first bomb was dropped on Hiroshima, and the second bomb was dropped on Nagasaki by the B-29 bombers named Enola Gay and Bockscar respectively.
Shortly after the end of the Second World War in 1945, the United Nations was founded. During the United Nation's first General Assembly in London in January 1946, they discussed the future of nuclear weapons and created the United Nations Atomic Energy Commission. The goal of this assembly was to eliminate the use of all Nuclear weapons. The United States presented their solution, which was called the Baruch Plan. This plan proposed that there should be an international authority that controls all dangerous atomic activities. The Soviet Union disagreed with this proposal and rejected it. The Soviets' proposal involved universal nuclear disarmament. Both the American and Soviet proposals were refused by the UN.
Some experimental scientists who worked directly with radioactive materials in this period may have been victims of radiation poisoning, often dying prematurely in the 1950s. These include Enrico Fermi, Igor Kurchatov, and Frédéric Joliot-Curie.
Early Cold War
Warhead development
In the years immediately after the Second World War, the United States had a monopoly on specific knowledge of and raw materials for nuclear weaponry. American leaders hoped that their exclusive ownership of nuclear weapons would be enough to draw concessions from the Soviet Union, but this proved ineffective.Just six months after the UN General Assembly, the United States conducted its first post-war nuclear tests — Operation Crossroads. The purpose of this operation was to test the effect of nuclear explosions on ships. These tests were performed at Bikini Atoll in the Pacific on 95 ships, including German and Japanese ships that were captured during World War II. One plutonium implosion-type bomb was detonated over the fleet, while the other one was detonated underwater.
In secrecy, the Soviet government was working on building its own atomic weapons. During the war, Soviet efforts had been limited by a lack of uranium, but new supplies discovered in Eastern Europe provided a steady supply while the Soviets developed a domestic source. While American experts had predicted that the Soviet Union would not have nuclear weapons until the mid-1950s, the first Soviet bomb was detonated on August 29, 1949. The bomb, named "First Lightning" by the West, was more or less a copy of "Fat Man", one of the bombs the United States had dropped on Japan in 1945.
Both governments spent massive amounts to increase the quality and quantity of their nuclear arsenals. Both nations quickly began the development of thermonuclear weapons, which can achieve vastly greater explosive yields. The United States detonated the first hydrogen bomb on November 1, 1952, on Enewetak, an atoll in the Pacific Ocean. Code-named "Ivy Mike", the project was led by Edward Teller, a Hungarian-American nuclear physicist. It created a cloud wide and high, killing all life on the surrounding islands. Again, the Soviets surprised the world by exploding a deployable thermonuclear device in August 1953, although it was not a true multi-stage hydrogen bomb. However, it was small enough to be dropped from an airplane, making it ready for use. The development of these two Soviet bombs was greatly aided by the Russian spies Harry Gold and Klaus Fuchs.
On March 1, 1954, the U.S. conducted the Castle Bravo test, which tested another hydrogen bomb on Bikini Atoll. Scientists significantly underestimated the size of the bomb, thinking it would yield 5 megatons. However, it yielded 14.8 megatons, the highest yield ever achieved by an American nuclear device. The explosion was so large the nuclear fallout exposed residents up to away to significant amounts of radiation. They were eventually evacuated, but most experienced radiation poisoning; and one person was killed, a crew member on a Japanese fishing boat which was from the bomb test site when the explosion occurred.
The Soviet Union detonated its first "true" hydrogen bomb on November 22, 1955, which had a yield of 1.6 megatons. On October 30, 1961, the Soviets detonated a hydrogen bomb with a yield of approximately 58 megatons.
With both sides in the Cold War having nuclear capability, an arms race developed, with the Soviet Union attempting first to catch up and then to surpass the Americans.