Canopus (nuclear test) in the context of Fangataufa

The Teller–Ulam design is the technical concept behind thermonuclear weapons, also known as hydrogen bombs. The design relies on the radiation implosion principle, using thermal X-rays released from a fission nuclear primary to compress and ignite nuclear fusion in a secondary. This is in contrast to the simpler design and usage of nuclear fusion in boosted fission weapons.

The design is named for scientists Edward Teller and Stanisław Ulam, who originally devised the concept in January 1951 for the United States nuclear weapons program, though their individual roles have been subsequently debated. The US Greenhouse George test in May 1951, the world's first artificial thermonuclear fusion, validated the radiation implosion principle. The US first tested the "true" Teller-Ulam design with the very high-yield Ivy Mike test in 1952. The design was independently devised and then tested by teams of nuclear weapons scientists working for at least four more governments: the Soviet Union in 1955 (RDS-37), the United Kingdom in 1957 (Operation Grapple), China in 1966 (Project 639), and France in 1968 (Canopus). There is not enough public information to determine whether India, Israel, or North Korea possess multi-stage weapons. Pakistan is not considered to have developed them. The Teller-Ulam design is the basis for all nuclear weapons tests above one megaton yield.

France is one of the five nuclear-weapon states recognized by the Non-Proliferation Treaty (NPT) but is not known to possess or develop any chemical or biological weapons. France is the only member of the European Union to possess nuclear weapons.

France was the fourth country to test a nuclear weapon, in 1960, and tested its first thermonuclear weapon in 1968. Charles de Gaulle was influential in the country's decision to develop both weapons and nuclear forces. France is also believed to have tested neutron bomb designs. The forces were developed in the late 1950s and 1960s to give France the ability to distance itself from NATO while still deterring the Soviet Union. France remains the only NATO member to not participate in its Nuclear Planning Group. France was the last of the five NPT-recognized nuclear-weapon states to ratify the treaty, in August 1992.