The Soviets demonstrated

The Soviets demonstrated the power of the "staging" concept in October 1961, when they detonated the massive and unwieldy Tsar Bomba, a 50 megaton hydrogen bomb that derived almost 97% of its energy from fusion. It was the largest nuclear weapon developed and tested by any country. HP Compaq HSTNNIB12 Battery

In 1954 work began at Aldermaston to develop the British fusion bomb, with Sir William Penney in charge of the project. British knowledge on how to make a thermonuclear fusion bomb was rudimentary, and at the time the United States was not exchanging any nuclear knowledge because of the Atomic Energy Act of 1946. HP Compaq HSTNN-IB16 Battery

However, the British were allowed to observe the American Castle testsand used sampling aircraft in the mushroom clouds, providing them with clear, direct evidence of the compression produced in the secondary stages by radiation implosion. HP Compaq HSTNN-IB18 Battery

Because of these difficulties, in 1955 British prime minister Anthony Eden agreed to a secret plan, whereby if the Aldermaston scientists failed or were greatly delayed in developing the fusion bomb, it would be replaced by an extremely large fission bomb. HP Compaq HSTNN-IB28 Battery

In 1957 the Operation Grapple tests were carried out. The first test, Green Granite was a prototype fusion bomb, but failed to produce equivalent yields compared to the Americans and Soviets, only achieving approximately 300 kilotons. HP Compaq HSTNN-IB51 Battery

The second test Orange Herald was the modified fission bomb and produced 700 kilotons—making it the largest fission explosion ever. At the time almost everyone (including the pilots of the plane that dropped it) thought that this was a fusion bomb. This bomb was put into service in 1958. HP Compaq HSTNN-IB52 Battery

A second prototype fusion bomb Purple Granite was used in the third test, but only produced approximately 150 kilotons.

A second set of tests was scheduled, with testing recommencing in September 1957. The first test was based on a "… new simpler design. HP Compaq HSTNN-IB55 Battery

A two stage thermonuclear bomb which had a much more powerful trigger". This test Grapple X Round C was exploded on November 8 and yielded approximately 1.8 megatons. On April 28, 1958 a bomb was dropped that yielded 3 megatons—Britain's most powerful test. HP Compaq HSTNN-IB62 Battery

Two final air burst tests on September 2 and September 11, 1958, dropped smaller bombs that yielded around 1 megaton each.

American observers had been invited to these kinds of tests. After their successful detonation of a megaton-range device HP Compaq HSTNN-LB05 Battery

(and thus demonstrating their practical understanding of the Teller–Ulam design "secret"), the United States agreed to exchange some of their nuclear designs with the United Kingdom, leading to the1958 US–UK Mutual Defence Agreement. HP Compaq HSTNN-LB08 Battery

Instead of continuing with their own design, the British were given access to the design of the smaller American Mk 28 warhead and were able to manufacture copies.

The People's Republic of China detonated its first H-Bomb using a Yu–Deng design June 17, 1967 ("Test No. 6"),HP Compaq HSTNN-LB0E Battery

a mere 32 months after detonating its first fission weapon (the shortest fission-to-fusion development in history), with a yield of 3.31 Mt.

The Yu–Deng design is different from the Teller–Ulam design. It doesn't use X-ray reflector, but refraction lens to achieve similar effect. HP Compaq HSTNN-LB11 Battery

India's first nuclear test occurred on May 18, 1974, which initially surprised the world. The first test, codename Smiling Buddha, was not a thermonuclear device according to the Bhabha Atomic Research Centre.^[19] On May 11, 1998, India reportedly detonated a thermonuclear bomb in its Operation Shakti tests ("Shakti-1", specifically). HP Compaq HSTNN-LB51 Battery

Dr. Samar Mubarakmand asserted that Shakti-1 was a successful test, but if it was a thermonuclear device as claimed, then it failed to produce certain results that were to be expected of a thermonuclear device.^[19]

Director for the 1998 test site preparations, Dr. K. Santhanam, HP Compaq HSTNN-LB52 Battery

reported the yield of thermonuclear explosion was lower than expected, although his statement has been disputed by other Indian scientists involved in the test.^[20] Indian sources, using local data and citing a US Geologic Survey report compiling seismic data from 125 IRIS stations across the world, HP Compaq HSTNN-MB05 Battery

argue that the magnitudes suggested a combined yield of up to 60 kilotonnes, consistent with the Indian announced total yield of 56 kilotonnesHowever, several independent experts have reported lower yields for the nuclear test and remained skeptical about the claims,^[19] and others have argued that even the claimed 50 kiloton yield was low for confirmation of a thermonuclear design. HP Compaq HSTNN-OB06 Battery

The Teller–Ulam design was for many years considered one of the top nuclear secrets, and even today it is not discussed in any detail by official publications with origins "behind the fence" of classification. United States Department of Energy (DOE) policy has been, HP Compaq HSTNN-OB52 Battery

and continues to be, that they do not acknowledge when "leaks" occur, because doing so would acknowledge the accuracy of the supposed leaked information.

Aside from images of the warhead casing, most information in the public domain about this design is relegated to a few terse statements by the DOE and the work of a few individual investigators. HP Compaq HSTNN-OB62 Battery

In 1972 the United States government declassified a statement that "The fact that in thermonuclear (TN) weapons, a fission 'primary' is used to trigger a TN reaction in thermonuclear fuel referred to as a 'secondary'", and in 1979 added, HP Compaq HSTNN-UB05 Battery

"The fact that, in thermonuclear weapons, radiation from a fission explosive can be contained and used to transfer energy to compress and ignite a physically separate component containing thermonuclear fuel." To this latter sentence they specified that "Any elaboration of this statement will be classified." HP Compaq HSTNN-UB11 Battery

The only statement which may pertain to the spark plug was declassified in 1991: "Fact that fissile and/or fissionable materials are present in some secondaries, material unidentified, location unspecified, use unspecified, and weapons undesignated." HP Compaq HSTNN-UB18 Battery

In 1998 the DOE declassified the statement that "The fact that materials may be present in channels and the term 'channel filler,' with no elaboration", which may refer to the polystyrene foam (or an analogous substance).^[25]

Whether these statements vindicate some or all of the models presented above is up for interpretation, HP Compaq HSTNN-UB68 Battery

and official U.S. government releases about the technical details of nuclear weapons have been purposely equivocating in the past (see, e.g.,Smyth Report). Other information, such as the types of fuel used in some of the early weapons, has been declassified, though of course precise technical information has not been. HP Compaq HSTNN-UB69 Battery

Most of the current ideas on the workings of the Teller–Ulam design came into public awareness after the Department of Energy (DOE) attempted to censor a magazine article by U.S. antiweapons activist Howard Morland in 1979 on the "secret of the hydrogen bomb". HP Compaq HSTNN-W42C Battery

In 1978, Morland had decided that discovering and exposing this "last remaining secret" would focus attention onto the arms race and allow citizens to feel empowered to question official statements on the importance of nuclear weapons and nuclear secrecy. HP Compaq HSTNN-W42C-A Battery

Most of Morland's ideas about how the weapon worked were compiled from highly accessible sources—the drawings which most inspired his approach came from none other than the Encyclopedia Americana. Morland also interviewed (often informally) many former Los Alamos scientists (including Teller and Ulam, HP Compaq HSTNN-W42C-B Battery

though neither gave him any useful information), and used a variety of interpersonal strategies to encourage informative responses from them (i.e., asking questions such as "Do they still use spark plugs?" even if he was not aware what the latter term specifically referred to).^[26] HP Compaq HSTNN-XB0E Battery

Morland eventually concluded that the "secret" was that the primary and secondary were kept separate and that radiation pressure from the primary compressed thesecondary before igniting it. When an early draft of the article, to be published in The Progressive magazine, HP Compaq HSTNN-XB11 Battery

was sent to the DOE after falling into the hands of a professor who was opposed to Morland's goal, the DOE requested that the article not be published, and pressed for a temporary injunction. The DOE argued that Morland's information was (1) likely derived from classified sources, HP Compaq HSTNN-XB18 Battery

(2) if not derived from classified sources, itself counted as "secret" information under the "born secret" clause of the 1954 Atomic Energy Act, and (3) was dangerous and would encourage nuclear proliferation.

Morland and his lawyers disagreed on all points, HP Compaq HSTNN-XB21 Battery

but the injunction was granted, as the judge in the case felt that it was safer to grant the injunction and allow Morland, et al., to appeal, which they did in United States v. The Progressive (1979).

Through a variety of more complicated circumstances, HP Compaq HSTNN-XB24 Battery

the DOE case began to wane as it became clear that some of the data they were attempting to claim as "secret" had been published in a students' encyclopedia a few years earlier. After another H-bomb speculator, Chuck Hansen, had his own ideas about the "secret" (quite different from Morland's) HP Compaq HSTNN-XB28 Battery

published in a Wisconsin newspaper, the DOE claimed that The Progressive case was moot, dropped its suit, and allowed the magazine to publish its article, which it did in November 1979. Morland had by then, however, changed his opinion of how the bomb worked, HP Compaq HSTNN-XB51 Battery

suggesting that a foam medium (the polystyrene) rather than radiation pressure was used to compress the secondary, and that in the secondary there was a spark plug of fissile material as well. He published these changes, based in part on the proceedings of the appeals trial, as a short erratum in The Progressive a month later. HP Compaq HSTNN-XB52 Battery

In 1981, Morland published a book about his experience, describing in detail the train of thought which led him to his conclusions about the "secret".^[26][28]

Morland's work is interpreted as being at least partially correct because the DOE had sought to censor it, HP Compaq HSTNN-XB59 Battery

one of the few times they violated their usual approach of not acknowledging "secret" material which had been released; however, to what degree it lacks information, or has incorrect information, is not known with any confidence. HP Compaq HSTNN-XB61 Battery

The difficulty that a number of nations had in developing the Teller–Ulam design (even when they apparently understood the design, such as with the United Kingdom), makes it somewhat unlikely that this simple information alone is what provides the ability to manufacture thermonuclear weapons. HP Compaq HSTNN-XB62 Battery

Nevertheless, the ideas put forward by Morland in 1979 have been the basis for all the current speculation on the Teller–Ulam design.

There have been a few variations of the Teller–Ulam design suggested by sources claiming to have information from inside of the fence of classification. HP Compaq HSTNN-XB68 Battery