In a nuclear war it will not make sense to use massed manpower. Any such concentration will provide too good a target for atomic weapons. To use big, costly and conspicuous machines of war will be unwise. Such machines will be defeated by nuclear explosions in the same way as the mailed knight went down before firearms. Any fighting unit in a nuclear war will have to be small, mobile, inconspicuous and capable of independent action. Such units whether on sea, land or in the air cannot rely and will not rely on fixed lines of supply. There will be no possibility and no need to occupy territory and to fight at fixed and definite fronts. If a war should be fought for military reasons and for military advantage, it will consist of short and sharp local engagements involving skill and advanced techniques and not involving masses that slaughter and are being slaughtered. If an invader adopts extreme dispersion, it will become impossible to defeat him with atomic weapons. But a very highly dispersed army can be defeated by a determined local population. Therefore the main role of nuclear weapons might well be to disperse any striking force so that the resistance of people defending their homes can become decisive. Nuclear weapons may well become the answer to massed armies and may put back the power into the hands where we believe it belongs: the hands of the people. At this point we are brought back to the main topic of this book: radioactivity. In a limited nuclear war the radioactive fallout will probably kill many of the innocent bystanders. We have seen that the testing program gives rise to a danger which is much smaller than many risks which we take in our stride without any worry. In a nuclear war, even in a limited one, the situation will probably be quite different. That noncombatants suffer in wars is not new. In a nuclear war, this suffering may well be increased further due to the radioactive poisons which kill friend and foe, soldier and civilian alike. Fortunately there exists a way out. Our early nuclear explosives have used fission. In the fission process a great array of radioactive products are formed, some of them intensely poisonous. More recently we have learned how to produce energy by fusion. Fusion produces fewer and very much less dangerous radioactivities. Actually the neutrons which are a by-product of the fusion reaction may be absorbed in almost any material and may again produce an assortment of radioactive nuclei. However, by placing only certain materials near the thermonuclear explosion, one may obtain a weapon in which the radioactivity is harmless. Thus the possibility of clean nuclear explosions lies before us.