The development of new techniques of initiating nuclear weapons has amplified the requirement for an accurate knowledge of the probability of initiation as a function of the various parameters involved. The results of the codes presently used to calculate these probabilities are self-consistent, but have been shown to be quite sensitive to the value of fission cross section used. Accordingly the critical assemblies group vas requested informally by small weapons division to investigate the feasibility of providing a prompt critical assembly which could give an experimental basis for normalization of the code results. A study of the various assemblies which met the requirements of this experiment was therefore conducted to determine which was best suited. The conclusion of the study is that a bare spherical oralloy assembly similar in operation to that of the Los Alamos Godiva would be the most suitable device with which to make these measurements. This conclusion was based on the fact that the prompt critical behavior of such a bare oralloy sphere is well understood and further, this behavior can be calculated by means of the present weapons codes. Such an assembly could be in operation in less than six months and would require an estimated total expenditure of $70,000 exclusive of the oralloy components.. Safety of operation could be insured by proper design of components, interlocks and operating procedures. The proposed assembly would be housed in the West Vault in Building 110 which can be made available in the near future. Much of the present instrumentation in the vault can be used for the new assembly. Some modification to the vault will be necessitated by the higher shielding requirements of the prompt assembly. Cost of these modifications is included in the basic cost estimate.