The development of thermonuclear weapons marked one of the major turning points in the history of Soviet-American strategic arms competition. In his book The Advisors Herbert York enhances our understanding of this turning-point by showing that the first Soviet thermonuclear device, which was exploded on 12 August 1953, was not a superbomb but had a different configuration and a substantially lower yield. York's analysis is important because it makes it possible to assess more accurately the progress of the Soviet nuclear weapons development in the 1950s, and to understand more clearly the nature of Soviet-American strategic arms competition.

The object of this note is to make public a document which gives more detailed information about Soviet nuclear weapons test in the 1950s. The data given here support York's analysis.