Two Bombs, One Satellite in the context of "Project 639"

639 was the codename for China's first full-scale test of a two-staged thermonuclear device, on 17 June 1967, yielding 3.3 megatons of TNT. It followed the first two-stage thermonuclear test, at a smaller 122 kt yield, in December 1966. It was the sixth nuclear test that was carried out by the People's Republic of China, and represented the completion of the "second bomb" i.e. thermonuclear bomb component of the "Two Bombs, One Satellite" program. With these two tests, China became the fourth nation to develop thermonuclear weapons, following the US, USSR, and UK. Taking place 32 months after the first Chinese nuclear test, Project 596, it remains the fastest progression from nuclear to full thermonuclear test of any country.