In the years after the 9/11 attacks, a new threat loomed large in the minds of policymakers and the public: the dirty bomb. This term describes a radiological weapon that used an explosive to disperse radioactive material over a limited area. A dirty bomb is far less powerful than a nuclear bomb, but it is easier and cheaper to assemble and can cause tremendous panic and disruption. Many analysts feared that terrorist groups would seek to develop and use such weapons: in 2002, US officials announced the detention of Jose Padilla, an American citizen and alleged al Qaeda operative who they insisted intended to detonate a dirty bomb in the United States. Since then, several governments in Europe have claimed to have foiled similar plots by terrorist groups.

But visions of dirty bombs and radiological terrorism obscured the fact that the threat from radiological weapons was not limited to terrorist groups. Indeed, for decades, major countries including the United States and the Soviet Union pioneered the development of these weapons. And now, as the norm against nuclear weapons is weakening and tensions between great powers mount, there is reason to worry that the dangers posed by radiological arms proliferation may be growing again.

In the past, at least five states expressed interest in weapons designed to disperse radioactive material without a nuclear detonation. Four states actively pursued them, and three—Iraq, the Soviet Union, and the United States—tested them on multiple occasions before ultimately choosing not to deploy them. The largely obscure history of the development of radiological weaponry helps to explain its appeal, especially in the context of rising international hostilities, a breakdown in nuclear arms control, and a loss of faith in the credibility of security assurances.

Russian disinformation about a purported covert Ukrainian radiological weapons program has brought renewed attention to the issue. Russia’s war against Ukraine and the attendant escalation in great-power competition have eroded the taboo against nuclear weapons use and undermined the international nonproliferation regime. Additional states may consider the possible deterrent benefits of possessing nuclear arms or, if the costs of acquiring such weapons are prohibitive, other nonconventional weapons. For these states, radiological weapons may appear a more viable option, something akin to “a poor man’s nuclear weapon.” Although US-led diplomatic efforts are now underway to ban them, radiological weapons are not prohibited under international law, which could encourage states to seek them out. Two decades ago, policymakers were haunted by visions of dirty bombs in the hands of terrorists. In the near future, however, they may have to grapple with the more dangerous possibility that states will once again turn to these lethal weapons.

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