The current WMD (Weapons of Mass Destruction) issue most significant to U.S. national security – utilizing a definition of WMD that focuses on CBRN (Chemical, Biological, Radiological, and Nuclear) threats – is that of biological weapons. Biological weapons pose a drastically more significant threat to the United States than chemical, radiological, or nuclear weapons. This is because an adversary may utilize them with stealth, without escalating the risk of kinetic conflict. An adversary would also experience a significant advantage in using biological weapons to sow confusion within the United States. Additionally, the COVID-19 pandemic – although not a result of foreign bioweapons (despite the claims of some of the world’s more rabid conspiracy theorists), has served as a test case for the United States’ response to biological attack.

First, unlike nuclear weapons, point out John P. Caves and Seth Carus in the publication The Future of Weapons of Mass Destruction, “the use of some chemical and biological weapons may be hard to attribute or be of sufficiently low lethality so as not to provoke an adversary to escalate to a more lethal response.” This means that the opportunity costs of using biological weapons against the United States are low for potential state or non-state adversaries. This low opportunity cost would make biological weapons particularly appealing to such hostile actors. Most concerning, in my own view, is the use of biological weapons by state actors that are seeking to exploit plausible deniability, rather than non-state actors seeking to prove a visible point.

Second, biological weapons provide a significant advantage to an adversary who wishes to sow confusion within the United States. An adversary would gain an advantage, for example, from targeting the U.S. military’s chain of command. It is important to note that this does not imply precision targeting, but rather an exploitation of biological weapons’ inherent imprecision to create chaos within the ranks. In pursuing the use of biological weapons to these ends, an adversary would rely on the fact that “a biological attack can range in operational decrement from that of a more limited impact to unit effectiveness due to lost duty days (e.g. norovirus outbreak) to catastrophic for affected units (e.g., pneumonic plague).”

Third, the COVID-19 pandemic provides a test case for how the United States might respond to a stealth biological attack. The “devastating social, economic and physical impact of the pandemic has […] raised questions about the consequences of a virus of similar ilk potentially being used deliberately as a weapon by a violent actor.”  While the U.S. House Committee on Oversight and Accountability in 2024 cited evidence of COVID-19 originating from a lab leak in Wuhan, China, there is not (at least at the time of this writing) any confirmed evidence to suggest that the pandemic’s spread was intentional. Nevertheless, a hostile foreign power may take lessons from the pandemic as to how to disrupt both government operations and daily life within the United States.

A counterargument to the idea that biological weapons are the most serious WMD threat facing the United States would likely purport, as does the United Nations Office of Disarmament Affairs, that “nuclear weapons are the most dangerous weapons on Earth”.  However, nuclear weapons serve a function that is based on deterring conflict through the credible threat of their use: on a global scale, argues veteran nuclear deterrence expert Keith B. Payne in his short volume Chasing a Grand Illusion, “nuclear weapons do indeed pose a risk to survival for many, but the lack of a nuclear deterrent can also be seen as posing a risk to the survival of many.” Add to this the difference in ease of attribution between nuclear weapons and biological weapons, and biological weapons prove a drastically more immediate threat.

Based on this analysis, biological weapons prove advantageous to adversaries due to several attributes. These include both the stealth with which biological weapons can be used and their capacity for disruption, as well as the historical precedent of COVID-19 as a biological phenomenon that upended U.S. society. Biological weapons are therefore the most substantive WMD threat to U.S. national security in 2025.