Molecular manufacturing raises the possibility of horrifically effective weapons. As an example, the smallest insect is about 200 microns; this creates a plausible size estimate for a nanotechnology-built antipersonnel weapon capable of seeking and injecting toxin into unprotected humans. The human lethal dose of botulism toxin is about 100 nanograms, or about 1/100 the volume of the weapon. As many as 50 billion toxin-carrying devices—theoretically enough to kill every human on earth—could be packed into a single suitcase.
Guns of all sizes would be far more powerful, and their bullets could be self-guided. Aerospace hardware would be far lighter and higher performance; built with minimal or no metal, it would be much harder to spot on radar. Embedded computers would allow remote activation of any weapon, and more compact power handling would allow greatly improved robotics. These ideas barely scratch the surface of what's possible.
An important question is whether nanotech weapons would be stabilizing or destabilizing. Nuclear weapons, for example, perhaps can be credited with preventing major wars since their invention. However, nanotech weapons are not very similar to nuclear weapons.
Nuclear stability stems from at least four factors. The most obvious is the massive destructiveness of all-out nuclear war. All-out nanotech war is probably equivalent in the short term, but nuclear weapons also have a high long-term cost of use (fallout, contamination) that would be much lower with nanotech weapons. Nuclear weapons cause indiscriminate destruction; nanotech weapons could be targeted. Nuclear weapons require massive research effort and industrial development, which can be tracked far more easily than nanotech weapons development; nanotech weapons can be developed much more rapidly due to faster, cheaper prototyping. Finally, nuclear weapons cannot easily be delivered in advance of being used; the opposite is true of nanotech. Greater uncertainty of the capabilities of the adversary, less response time to an attack, and better targeted destruction of the enemy's resources during an attack all make nanotech arms races less stable. Also, unless nanotech is tightly controlled, the number of nanotech nations in the world could be much higher than the number of nuclear nations, increasing the chance of a regional conflict blowing up.
Admiral David E. Jeremiah, Vice-Chairman (ret.), U.S. Joint Chiefs of Staff, in an address at the 1995 Foresight Conference on Molecular Nanotechnology said: "Military applications of molecular manufacturing have even greater potential than nuclear weapons to radically change the balance of power."
An excellent essay by Tom McCarthy explores these points in more detail. He discusses the ways that nanotechnology can destabilize international relations: It will reduce economic influence and interdependence, encourage targeting of people as opposed to factories and weapons, and reduce the ability of a nation to monitor its potential enemies. It may also, by enabling many nations to be globally destructive, eliminate the ability of powerful nations to "police" the international arena. By making small groups self-sufficient, it can encourage the breakup of existing nations.
Industry groups will generally say that these conclusions are far-fetched, or at least so remote that they need not alarm us now. But CRN believes nanotechnology development could accelerate at such a pace that we might be caught unaware and unprepared.