Since their introduction in 1945, nuclear explosives have been the most feared of the weapons of mass destruction, in part because of their ability to cause enormous instantaneous devastation and of the persistent effects of the radiation they emit, unseen and undetectable by unaided human senses. The Manhattan Project cost the United States $2 billion in 1945 spending power and required the combined efforts of a continent-spanning industrial enterprise and a pool of scientists, many of whom had already been awarded the Nobel Prize and many more who would go on to become Nobel Laureates. This array of talent was needed in 1942 if there were to be any hope of completing a weapon during the Second World War. Because nuclear fission was discovered in Germany, which remained the home of many brilliant scientists, the United States perceived itself to be in a race to build an atomic bomb.When the Manhattan Project began far less than a microgram of plutonium had been made throughout the world, and plutonium chemistry could only be guessed at; the numbers of neutrons released on average in U-235 and Pu-239 fissions were unknown; the fission cross sections (probabilities that an interaction would occur) were equally unknown, as was the neutron absorption cross section of carbon. experiment. Although talented people are essential to the success of any nuclear weapons program, the fundamental physics, chemistry, and engineering involved are widely under-stood; no basic research is required to construct a nuclear weapon. Therefore, a nuclear weapons project begun in 1996 does not require the brilliant scientists who were needed for the Manhattan Project. For many decades the Manhattan Project provided the paradigm against which any potential proliferator’s efforts would be measured. Fifty years after the Trinity explosion, it has been recognized that the Manhattan Project is just one of a spectrum of approaches to the acquisition of a nuclear capability. At the low end of the scale, a nation may find a way to obtain a complete working nuclear bomb from a willing or unwilling supplier; at the other end, it may elect to construct a complete nuclear infrastructure including the mining of uranium, the enrichment of uranium metal in the fissile isotope U-235, the production and extraction of plutonium, the production of tritium, and the separation of deuterium and 6 Li to build thermonuclear weapons. At an intermediate level, the Republic of South Africa constructed six quite simple nuclear devices for a total project cost of less than $1 billion (1980’s purchasing power) using no more than 400 people and indigenous technology.
Fissile materials can produce energy by nuclear fission, either in nuclear reactors or in nuclear weapons. A country choosing to join the nuclear weapons community must acquire the necessary weapons (fissile) material (U-235 U or Pu-239). It is generally recognized that the acquisition of fissile material in sufficient quantity is the most formidable obstacle to the production of nuclear weapons. Fissile material production consumes the vast majority of the technical, industrial, and financial resources required to produce nuclear weapons. For example, production of fissile materials —- highly enriched uranium (HEU) and plutonium —- accounted for more than 80 percent of the $1.9 billion (1945 dollars) spent on the Manhattan Project.
Some analysts believe that the difficulties of enriching uranium are offset by the simpler weapon designs which enriched uranium allows. In the United States, HEU is considered less expensive to use in a weapon than plutonium. Operation of a reactor to produce plutonium requires the extraction and purification of uranium and, in some cases, at least modest enrichment. Given international safeguards on reactors using enriched uranium obtained from another nation or heavy water moderated reactors, a proliferant may be forced in any case to construct an enrichment facility. The choice is likely to be determined by the indigenous availability of uranium and the national surplus (or shortage) of electricity.Acquisition of a militarily significant nuclear capability involves, however, more than simply the purchase or construction of a single nuclear device or weapon. It requires attention to issues of safety and handling of the weapons, reliability and pre-dictability of entire systems, efficient use of scarce and valuable special nuclear material (SNM) (plutonium and enriched uranium), chains of custody and procedures for authorizing the use of the weapons, and the careful training of the military personnel who will deliver weapons to their targets. In contrast, a nuclear device used for terrorism need not be constructed to survive a complex stockpile-to-target sequence, need not have a predictable and reliable yield, and need not be efficient in its use of nuclear material. Although major acts of terrorism are often rehearsed and the terrorists trained for the operation, the level of training probably is not remotely comparable to that necessary in a military establishment entrusted with the nuclear mission. The United States has developed a complex and sophisticated system to ensure that nuclear weapons are used only on the orders of the President or his delegated representative. Some elements of the custodial system are the “two-man rule,” which requires that no person be left alone with a weapon; permissive action links (PALs), coded locks which prevent detonation of the weapon unless the correct combination is entered; and careful psychological testing of personnel charged with the custody or eventual use of nuclear weapons. In addition, U.S. nuclear weapons must be certified as “one point safe,” which means that there is less than a one-in-a-million chance of a nuclear yield greater than the equivalent of four pounds of TNT resulting from an accident in which the high explosive in the device is detonated at the point most likely to cause a nuclear yield. It is believed to be unlikely that a new proliferator would insist upon one point safety as an inherent part of pit design; the United States did not until the late 1950’s, relying instead upon other means to prevent detonation (e.g., a component of Little Boy was not inserted until after the Enola Gay had departed Tinian for Hiroshima). It is also unlikely that a new actor in the nuclear world would insist upon fitting PALs to every (or to any) nuclear weapon; the United States did not equip its submarine-launched strategic ballistic missiles with PALs until, at the earliest, 1996, and the very first U.S. PALs were not introduced until the mid-1950’s, when American weapons were stationed at foreign bases where the possibility of theft or misuse was thought to be real. Nonetheless, any possessor of nuclear weapons will take care that they are not used by unauthorized personnel and can be employed on the orders of duly constituted authority. Even -— or, perhaps, especially -— a dictator such as Saddam Hussein will insist upon a fairly sophisticated nuclear chain of command, if only to ensure that his weapons cannot be used by a revolutionary movement. It is also quite likely that even the newest proliferator would handle his weapons with care and seek to build some kind of safety devices and a reliable SAFF system into the units. On the basis of experience, one might expect to observe significant nuclear planning activity and the evolution of situation-specific nuclear doctrine on the part of a new proliferator who would have to allocate carefully the “family jewels.” The development of a nuclear strategy might be visible in the professional military literature of the proliferator.