There can be no doubt that the desire for peace is most deep, and this desire is felt by all thinking and honest people on our earth. All of us certainly hope that the catastrophe of war can be avoided. This great and universal wish for peace is the driving force behind the desire for disarmament. In the minds of most people it would be an important step toward disarmament if the testing of nuclear weapons were stopped by all nations. This belief is widely held, but it is not necessarily well-founded. In fact, there are arguments on the other side which should be considered carefully. It is generally believed that the First World War was caused by an arms race. For some strange reason most people forget that the Second World War was brought about by a situation which could be called a race in disarmament. The peace-loving and powerful nations divested themselves of their military power. When the Nazi regime in Germany adopted a program of rapid preparation for war, the rest of the world was caught unawares. At first they did not want to accept the fact of this menace. When the danger was unmistakable, it was too late to avert a most cruel war, and almost too late to stop Hitler short of world conquest. Unfortunately, disarmament is safe only when no one wants to impose his will by force of arms upon his neighbors. In the uneasy world in which we live today no reasonable person will advocate unilateral disarmament. What people hope is that all sides will agree to reduce their military power and thereby contribute to a more peaceful atmosphere. The elimination of tests has appeared possible and proper for two reasons. One is that tests are conspicuous, and therefore it is believed that we can check whether or not testing has actually been stopped by everyone. The second reason is that nuclear explosives already represent such terrifying power that further tests appear useless and irrational. These arguments are simple and almost universally accepted. They are based on misconceptions. A nuclear explosion is a violent event, but in the great expanses of our globe such tests can be effectively hidden if appropriate care is taken to hide them. There can be no doubt that this is possible. The question is only how much it costs to hide a test and how big is the explosion that can be carried out in secret for a certain amount of expenditure.