In 1955 the United States and the Soviet Union were matching steps in a race to develop missiles tipped with thermonuclear weapons. American officials were frustrated and alarmed by their inability to learn the scale and progress of the Soviet program, which directly threatened the security of the United States, and they were convinced that serious arms control measures required reliable means for mutual inspection. The result: President Dwight D. Eisenhower's dramatic Open Skies proposal, advanced--and rejected--at the Geneva summit of 1955.