All the knowledge required to manufacture nuclear bombs is now available in public libraries in unclassified literature. A few individuals with very limited practical experience could produce small bombs within a short time if they could obtain the necessary raw materials; the resources necessary for the manufacture of a few rudimentary nuclear weapons are within the means of many nations. The essentials are a cadre of trained personnel; uranium; an industrial base adequate to permit the construction of a nuclear reactor; and auxiliary facilities large enough to provide the necessary quantities of plutonium. Thus many nations possess resources sufficient to undertake, without special outside assistance, the manufacture of rudimentary nuclear weapons, given the national will to do so and the readiness, in some cases, to forego the benefits from the endeavours to which those resources might otherwise be applied. The time required would vary among the group of countries, and for those which have only the minimum resources, it might be up to ten years or more. At the upper end of the scale, highly industrialized nations, with substantial national income, large numbers of trained scientific, technical and managerial personnel, and a reasonably accessible source of uranium, could become capable of manufacturing rudimentary nuclear weapons within a few years.