The first proposal, for "low-yield weapons," refers to bombs that would explode in the air with a power perhaps a hundred times smaller than that of the Hiroshima weapon. Deterrence theorists argue that these bombs—which would have a power equivalent to about 100 tons of TNT—would fill a critical gap between the least powerful nuclear weapons in the current arsenal (equivalent to about 300 tons of TNT) and the most powerful conventional bombs (equivalent to about 10 tons of TNT). Yet it is highly unlikely that an enemy who was undeterred by the prospect of a salvo of 10-ton conventional bombs would think again when confronted with a 100-ton nuclear weapon.
The second proposal, for "EPWs"—known colloquially as "bunker-busters"—makes little more sense. Much of the public debate on these weapons has centred on relatively small versions, and whether they could be made fallout-free (they could not). In fact the most compelling case for such bombs requires that they be made as powerful as possible. According to this line of argument, EPWs should be designed to threaten targets deeper underground than those that can be reached today. This is the best way to deter enemy leaders who might hide underground from attacking US interests.
The trouble is that the proposed designs would improve the reach of US nuclear weapons by a factor of two at best, and even then would produce vast amounts of fallout. An enemy could simply dig deeper underground—or site its facilities within a hundred miles of an urban center.
"Enhanced radiation weapons," the third option, are best known as "neutron bombs"—a technology debated and rejected during the 1980s. The purpose of such weapons is to kill enemies with radiation while preserving the physical infrastructure nearby.
During the cold war, proponents of the neutron bomb argued with some credibility that it would be effective against massed Soviet armour, at the time considered the greatest threat to western security. But even then, hawkish opponents of the proposed bombs countered that precision-guided conventional munitions could do the job better. Today, with precision-guided weaponry much more mature, and no potential enemy possessing a massive armored capability, there is no credible rationale deterrence-based or not for such a weapon.
The conference's last proposal, for "agent-defeat" weapons, is, from a military perspective, perhaps the most interesting. These weapons would be designed to penetrate facilities stockpiling chemical or biological weapons and to incinerate them, thus preventing the spread of the deadly agents. But recent studies—including one by Michael May, former director of the Livermore National Laboratory—have questioned these claimed capabilities. Moreover, conventional weapons—ranging from bleach-filled bombs to special incendiary weapons—show equal, if not greater, promise.
Besides, without precise intelligence, of the kind the US apparently lacked in Iraq, targeting such bombs would be impossible. On occasion, they might destroy isolated caches of illicit weapons. But they would never credibly threaten a large fraction of an enemy's stockpiles—and thus would be ineffective as a deterrent.
Advocates of these new weapons continue to insist that they would be only for deterrence. Yet all the technical evidence suggests that they would add nothing to the deterrent capabilities of America's existing arsenal. That means that, if they are ever built, these weapons will have primarily offensive roles.
America's lawmakers are presumably acting in good faith in supporting these developments. But they should think again before committing their country to costly programmes that will do little to protect it—and much to alienate its international friends.