Initially, France did not explore thermonuclear weapons; instead it focused on large, advanced fission weapons. When it was realized that China was developing the hydrogen bomb, top priority was given by de Gaulle to France's fusion weapons program.[2] Development of thermonuclear weapons began sometime in July 1962 and the first theoretical breakthroughs would come in 1965 with the development of several conceptual ideas. Physcist Luc Dagens became head of thermonuclear weapons research at this time at the Centre d'Etudes de Limeil-Valenton.

Minimal progress was made for thermonuclear weapons research in 1966. As a result, in April the development team was split into two groups, both of which would develop different designs. Robert Dautray, who was the scientific director at DAM (La Direction des Applications Militaires), initiated the split following pressure from his superiors.[3] The departure of physicist Pierre Billaud saw the thermonuclear weapons program go down two separate paths.

Theoretical advances in radiation implosion were made by Billaud in Janurary 1967. In April, Physicist Michel Carayol published a paper in which it was outlined architectural ideas and solutions for an efficient thermonuclear device. The Carayol paper was considered a major leap in the development of a hydrogen bomb. The theoretical solutions for a two-stage thermonuclear device had been finalized following several years of research.

Fangataufa Atoll

On 27 June 1967, the Antares nuclear test was conducted at Mururoa. This was an experimental thermonuclear device developed by the Dagens group at Limeil. It yielded 150 kilotons and was considered to be disappointing.[2]

At the time, France did not have the means to produce the materials needed for a two-stage thermonuclear device. 151 tons of heavy water was purchased from Norway and an additional 168 tons from the U.S. The terms under which France purchased the heavy water from the United States stated it could not be used for military purposes. However, the terms for the deal with Norway were never disclosed. Most likely this heavy water went into the Celestin reactors in 1967 to produce tritium needed for the device.

On 4 and 5 September 1967, a meeting was held in the DAM center in Valduc (in Burgundy) for all scientists and engineers working on the thermonuclear problem. It was decided to test two different experimental thermonuclear devices during the 1968 campaign; one of which was based on designs by Luc Dagens. The other device was to tested was one based on Carayol's design.

On 29 September 1967, two designs were finalized and added to the 1968 test schedule. These two experimental devices were expected to yield different results. The Dagens design was predicted to have a yield of several megatons. The Carayol design, which was described as being in the “extreme” was expected to have only a one megaton yield; however, this device was also predicted to be much more efficient.[2]

Jacques Bellot was charged with developing the multi-megaton thermonuclear device; while Pierre Billaud was made responsible for the development of the advanced thermonuclear yield device. The test of the Dagens device, code named Canopus, was scheduled to be fired first. The Carayol device was to be fired several weeks later; the test was code named Procyon

Due to the expected high yield of the two shots, it was decided to fire them on separate atolls. Fangataufa was selected to be the location for the Canopus shot, while Procyon would be fired on the western end of Mururoa atoll. These two tests would also be the last two fired during the 1968 campaign as it was anticipated that radiological contamination of the atolls following the tests would make them uninhabitable for some time.

France announced its intention of testing a hydrogen bomb in the late 1960s. This news provoked the People’s Republic of China to conduct a full scale thermonuclear test on June 17, 1967.[4] The 3.3 megaton device was dropped from a Hong-6 bomber over the nuclear test site at Lop Nor.

Clemenceau

The 1968 campaign also proof tested the MR-41 warhead. The MR-41 was the first boosted fission weapon France stockpiled and also France’s most powerful non-thermonuclear warhead. It was stockpiled from 1971 to 1979 and armed the MSBS M1 and M2 SLBMs. The initial development of the MR-41 began in 1963, and later continued from 1966 to 1971. The weapon used deuterium and tritium to boost the highly enriched uranium.

Some 5,936 uniformed personnel were stationed at Mururoa, Fangataufa, Hao, and Tahiti for the 1968 campaign, with an additional 2,265 civilian technicians. The aircraft carrier Clemenceau, sailed to French Polynesia to participate in four of the shots (Capella, Castor, Pollux, and Canopus). Three additional cruisers also participated along with the Clemenceau in the series, increasing the number of personnel by 7,018.