By its fifth test, Britain was moving toward thermonuclear weapons. The second of two tests in the Mosaic series, its fifth test was similar to the fourth Soviet test—it involved a device using layers of thermonuclear material. As Lorna Arnold and Mark Brian Smith wrote in Britain, Australia and the Bomb, the Mosaic series “made essential contributions” to Britain’s development of thermonuclear weapons. British scientist William Penney said the purpose of the tests was “to confirm that we have not made a fundamental mistake.” They had not. The British would test a thermonuclear weapon in 1957, ultimately pushing the United States to resume nuclear-weapons cooperation with Britain, cooperation that continues to this day.
Mosaic helped the United States come to regard the British as a full-fledged nuclear power, a precedent that might pique Kim Jong Un’s interest.
France: In Eker, Algeria, November 7, 1961
France’s fifth test was a science experiment. Its first four tests, conducted in the atmosphere over Algeria, had demonstrated a compact nuclear device weighing 1,200 kilograms. With Algerian independence looming, France moved its nuclear testing underground, to a location near the village of In Eker.
The fifth French test, code-named “Agate,” was the first of a series of 18 underground nuclear tests at the site through 1966, when local opposition forced France to move its testing to the South Pacific. In the 1960s, the ability to conduct nuclear tests underground was considered a sign of technical sophistication. French officials were justly proud of the achievement, which would elude the Chinese in the years to come. Of course, underground testing no longer seems to be the challenge it once was. All of North Korea’s tests have been conducted underground.
China: Lop Nor, December 28, 1966
The final fifth test was very nearly a thermonuclear device. China’s fifth nuclear test was a “principles” test of a thermonuclear device. By this point, China had already tested fission devices dropped by aircraft and carried by a missile, as well as a layer-cake device like the one involved in the fifth British test. China’s next test, in June 1967, would be a massive, staged-thermonuclear weapon with a yield of more than three megatons.
The notion of Mao Zedong’s China developing nuclear weapons, then moving swiftly to thermonuclear weapons, certainly grabbed the world’s attention in the 1960s. Mao’s China was considered a sort of backward oddity, a country with no business developing the most sophisticated nuclear weapons, let alone doing so in less than three years—and before a European power like France. Thermonuclear weapons were incongruous with the popular image of China in the 1960s. Sound familiar?
Although each of these countries made different choices over what to prioritize, by their fifth nuclear tests each had dramatically reduced the size of nuclear weapons from the giant “Fat Man” bomb that the United States dropped on Nagasaki, and was well on its way to developing thermonuclear weapons with yield ranges in the megatons. Five nuclear tests is quite a lot, and the later countries like France and China were able to move quickly by following the path set forth by the United States and Soviet Union.
North Korea is coming last, in an era when these technologies are 50 years old and have been demonstrated repeatedly by other nuclear powers. In this context, the country’s boasts about building nuclear weapons small enough to arm missiles and making use of thermonuclear materials don’t seem outlandish at all.