Global Policy Forum

By Michael Levi

During the 1991 Gulf War, as U.S. smart bombs picked off Iraqi targets, would-be adversaries of the United States learned an important lesson: In order to protect valuable military assets, such as command centers and stockpiles of chemical and biological weapons, the best bet may be to bury them deep underground in fortified bunkers or beneath a granite mountain. In the years following Operation Desert Storm, U.S. military planners debated how to destroy such "hardened" targets. Aggravating this dilemma, if the United States bombed weapons stockpiles, the attack could disperse chemical and biological agents, causing widespread havoc.

One proposed solution is small "mini-nukes" that burrow underground before detonating, thereby destroying hardened targets while reducing collateral damage from radioactive fallout. Because of the heat and radiation they produce, some advocates claim these bombs could neutralize the chemical or biological agents in their target, further reducing unnecessary damage.

Although proposals for bunker-busting nuclear warheads have been around for years, the Bush administration's 2002 Nuclear Posture Review (NPR) explicitly endorsed their pursuit. Unsurprisingly, arms control advocates weren't pleased. In a representative critique, the San Francisco-based Global Security Institute warned that the NPR represented a "major shift in the military and ethical rationale for nuclear weapons, no longer defining them as devices of deterrence, but as weapons of war." Malaysia's ambassador to the International Atomic Energy Agency warned that the United States risks undermining the Nuclear Non-Proliferation Treaty by following "a double standard that allows it to develop and threaten to use nuclear weapons while denying them to smaller countries." Other critics ridicule the bunker-busting concept as immaculate preemption, expressing skepticism that even a comparatively small nuclear explosion can be used as a precision instrument that tidies up after itself.

This debate has added momentum to scientific assessments of the efficacy and safety of mini-nukes. However, as several recent articles indicate, what constitutes hard scientific fact remains a matter of ambiguity and interpretation. In a recent issue of Science & Global Security, two articles assess the ability of nuclear bombs to neutralize chemical and biological agents. In the first paper, "Effectiveness of Nuclear Weapons Against Buried Biological Agents," authors Michael May and Zachary Haldeman of Stanford University caution that "whether all of the bio-agents in a given storage configuration are sterilized depends pivotally on the details of the storage configuration." They are optimistic that a cache of chemical agents stored near the Earth's surface could be destroyed, while they are more pessimistic about the prospects of destroying agents stored throughout a deep, dispersed facility.

Princeton University's Robert Nelson, writing in the same issue, appears more certain that live agents will effectively disperse, but a careful reading of his paper suggests that he, too, is unsure. In his article, "Nuclear ‘Bunker Busters' Would More Likely Disperse than Destroy Buried Stockpiles of Biological and Chemical Agents," Nelson begins with a simple argument: There is not enough energy in a nuclear explosion to heat—and thus sterilize—all the material it ejects. Therefore, unless the biological or chemical agent target is extremely close to the nuclear explosion, at least some of it will be ejected without being sterilized. Nelson does not calculate, however, whether far-flung residues of chemical and biological agents will still be live, or whether all such residues might be raised to high temperatures and thus rendered harmless.

Four scientists from Los Alamos National Laboratory offer a more upbeat assessment in their article "An Analysis of Reduced Collateral Damage Nuclear Weapons," appearing in Comparative Strategy. The authors show that, compared to a weapon detonated at the Earth's surface, a small nuclear bomb that penetrates the ground 10 meters before exploding can be roughly 40 times smaller and still destroy the same target. Thus, switching to this smaller bomb would reduce the area affected by radioactive fallout by a factor of about 10. The authors consider this reduced fallout a powerful reason to pursue the new bombs.

But why is reducing collateral deaths from hundreds of thousands to tens of thousands such a worthwhile goal, especially for a weapon that has caused no deaths in nearly 60 years? Moreover, does it matter if one nuclear weapon is cleaner than another when conventional alternatives—such as sealing off bunkers or deploying high-temperature weapons to neutralize biological agents—might be available? The Los Alamos authors argue that the threat to retaliate with nuclear weapons will be more credible with the reduced fallout; as a result, enemies will be more effectively deterred. The scientists cannot, however, explain why these bombs would be preferable to conventional weapons, contending only that the goal "is not to compete as an alternative to conventional weapons." That may be true in a narrow sense, but policymakers would be wise to carefully compare the two options before risking the radioactive and political fallout from deploying mini-nukes.

Michael Levi is a science and technology fellow at the Brookings Institution in Washington, D.C.