This lengthy report was State Department Bureau of Intelligence and Research's contribution to the first National Intelligence Estimate on the nuclear proliferation, NIE 100-6-57. Written at a time when the United States, the Soviet Union, and the United Kingdom were the only nuclear weapons states, the “Fourth Country” problem referred to the probability that some unspecified country, whether France or China, was likely to be the next nuclear weapons state. Enclosed with letter from Helmut Sonnenfeldt, Division of Research for USSR and Western Europe, to Roger Mateson, 4 June 1957, Secret

This document describes the differing views regarding safeguards. The Canadians strongly supported the former, “full scope safeguards” (their terminology, which caught on), which the French saw as “tantamount to imposing NPT obligations”--a reference to the Treaty’s Article III--which they would not accept. Arguing that full-scope safeguards was “alien to [their] philosophy,” the French suggested that a “traditional interpretation of the contamination principle (i.e., requiring safeguards on any materials produced in exported facilities),” would make it possible to achieve “the practical equivalent” of the Canadian proposal.