FOREWORD In 1954 the United States had already begun research to find means of drastically reducing the proportion of fission yield required in the thermonuclear explosion. This was an effort to develop nuclear explosives whose residual radioactivity could be confined more nearly to the area of blast and thermal damage, and to reduce greatly the amount of radioactive fallout which would be created from such explosions and given world-wide distribution. In July, 1956, the United States announced that it had achieved initial success in this program and in test firings had found that, with further development, weapons of drastically reduced fission yield could be produced. The United States has with high priority continued the developmentof weapons of greatly reduced fission yield in proportion to total yield. A large portion of the current test series (Hardtack) is being devoted to making possible a material increase in the number of reduced-fission type weapons that can be produted., On April 25, 1958, the United Nations, on behalf of the United States, offered to nations represented on the U. N. Scientific Committee on the effects of atomic radiation an invitation for their representatives to observe a demonstration of the firing of a weapon of greatly reduced fission yield. This demonstratian will provide opportunity for the U. N. Observers to witness the firing of such a device and to make a determination, through instrumentation and laboratory analyses, of the weapon's total and fission yield. It is the purpose of this handbook to describe briefly the operational procedure to be followed for the U. N. observance, the instrumentation to be used, and the analyses to be made. , g