" Dark Sun: The Making of the Hydrogen Bomb covers more than the title suggests. The narrative begins with Soviet espionage in the 1940s, coving such figures as the physicist Klaus Fuchs, the courier Harry Gold, David Greenglass the enlisted man at Los Alamos, and the Rosenbergs. These figures and others provided the Soviets with a good deal of information about the atomic bomb program, in particular the existence of plutonium and the use of implosion to create a plutonium bomb (as opposed to a bomb made from Uranium 235). Rhodes' discussion of Soviet espinoage is incomplete, for two reasons. First, when the book was published in 1995, much less material was available on the American Venona project to decrypt Soviet messages that were first coded and then enciphered with a one time pad (the one time pads were in fact used more than once, which was what allowed the Americans to decrypt many but not all messages or portions there of). This material extends our knowledge of Soviet espionage. Second, there was at least one more physicist at Los Alamos who was a Soviet spy. As I recall, the more recent book on the subject of nuclear weapons, The First War of Physics has more material on these matters. Rhodes' book is still valuable, because it has more material on the technical issues, as well as being wonderfully written. The material on fission bombs (like those dropped on Japan) is important because a fission bomb is needed to trigger fusion in a hydrogen bomb. Hydrogen bombs can be made much more powerful than a fission only bomb. Rhodes covers both the American and Soviet programs. To me, it seems likely that the Soviets would have eventually learned all they needed to on their own without spying, but that espionage speeded their work up considerably. They probably also learned about early (middle of the 1940s) ideas on how to design a fusion weapon. Edward Teller had been working on a fusion weapon since the 1940s. As Teller became fixated on an unworkable idea to make a hydrogen bomb, this particular variant known as the Super, and remained fixated on it until 1949 or 1950, the ironic circumstance arose that the primary advocate of a fusion weapon probably helped slow its development. A different idea of Teller's, which was also developed by the Soviets for their first thermonuclear device, known as the Alarm Clock, could have been developed some years before the United States first exploded a thermonuclear device in the autumn of 1952, but would have resulted in a much smaller (and thus to Teller unsatisfactory) explosion. In the early 1950s the collaboration between Edward Teller and the mathematician Stanislaw Ulam lead to a workable design for a multi-megaton hydrogen bomb. One interesting aspect of hydrogen bomb development was that it was impossible to meaningfully test any of its components separately to see if it would work. This aspect made it different from the fission bomb, where some experimental tests could be done without a tremendous explosion occurring (which doesn't mean that these tests weren't scary). As a consequence of this limitation, the hydrogen bomb was much more dependent upon numerical simulations to test and improve designs, prior to testing the bomb by exploding one. These simulations were very difficult for a staff using mechanical calculating machines and slide rules, and some could only be done using early electronic computers. As the computers were just being built at the time, the American development of the hydrogen bomb was sometimes delayed by the need to wait for the computer to be built. Rhodes' also covers the deployment of the American strategic bomber command which would use the bombs. Curtis LeMay was the most important commander of this Air Force unit in the 1940s and 1950s. LeMay was a very able commander who prepared his unit well. He also had some views that to me seem way to close to advocating preemptive nuclear war. He continued to advocate similar views when he was the chief of staff of the Air Force during the Cuban Missile Crisis. During much of this period, in the United States there was a perception that the Soviet Union was quickly overtaking the United States in its nuclear capabilities. Sufficient evidence of successful Soviet espionage had come out in various trials (the Rosenbergs and Fuchs trials for example) that many people were quite jumpy. In addition, Edward Teller was unhappy with the rate at which the United States was developing a hydrogen bomb. These aspects converge in the administrative hearing regarding whether or not Robert Oppenheimer, the first head of the American nuclear weapons laboratory at Los Alamos and a government advisor in the 1940s and early 1950s, should continue to have a security clearance. Oppenheimer was vulnerable in general terms because both his wife and brother Frank had been members of the Communist Party. He himself had been a fellow traveler. More specifically damaging, he had been approached to provide information to the Soviets about the atomic bomb program in the 1940s, and had told two different and contradictory stories about it to government officials. He does not seem to have been a spy, though I don't know what the Venona materials might indicate about this matter. These contacts were old news by the time of his hearing, but the context had changed and also Teller had come to blame Robert Oppenheimer for the lack of progress on the hydrogen bomb (though by the time the hearing occurred a thermonuclear device had alread been tested in the Pacific). Oppenheimer lost his clearance, and Teller lost the goodwill of many of his colleagues for his testimony during the hearing. "
— Converse, 1/14/2014