Atomic spies " Atomic spies " or " Atom spies " were people in the United States , Great Britain , and Canada who are thought to have illicitly given information about nuclear weapon s production or design to the Soviet Union during World War II and the early Cold War . Exactly what was given , and whether everyone on the list gave it , is still a matter of some scholarly dispute , and in some cases what were originally seen as strong testimonies or confessions were admitted as fabricated in later years . Their work constitutes the most publicly well - known and well - documented case of nuclear espionage in the history of nuclear weapons . There was a movement among nuclear scientists to share the information with the world scientific community , but that was firmly quashed by the U . S . government . Whether the information significantly aided the speed of the Soviet atomic bomb project is also disputed . While some of the information given could have aided in developing a nuclear weapon , the manner in which the heads of the Soviet bomb project actually used the information has led scholars to doubt its role in increasing the speed of development . According to this account , Igor Kurchatov and Lavrenty Beria used the information primarily as a " check " against their own scientists ' work and did not liberally share the information with them , distrusting both their own scientists as well as the espionage information . Later scholarship has also shown that the decisive brake on early Soviet development was not problems in weapons design but , as in the Manhattan Project , the difficulty in procuring fissile materials , especially since the Soviet Union had no uranium deposits known when it began its program ( unlike the United States ) . Confirmation about espionage work came from the VENONA project , which intercepted and decrypted Soviet intelligence reports sent during and after World War II . These provided clues to the identity of several spies at Los Alamos and elsewhere , some of whom have never been identified . Some of this information was available , but not usable in court for secrecy reasons , during the trials of the 1950s . Additionally , records from Soviet archives , which were briefly opened to researchers after the fall of the Soviet Union , included more information about some spies . Importance of atomic spies . Before the beginning of World War II , the theoretical possibility for nuclear fission was a highly discussed topic among the top physicists in the world . Scientists from the Soviet Union were later recognized for their contributions to the understanding of a nuclear reality , and were awarded several Nobel Prizes . Igor Kurchatov , L . D . Landau , Kirill Sinelnikov , were among those Soviet Scientists that helped establish , and prove the existence of a splittable atom . Dwarfed by , and lost upon the scale of the Manhattan Project , the significance of the contributions are rarely understood , and credited , outside of the field of physics . According to several sources , it was understood on a theoretical level that the atom provided for extremely powerful and novel releases of energy , and could possibly be utilized in the future for military purposes . In recorded comments made by the physicists themselves , they lamented over their inability to achieve any kind of practical application from the discoveries . This would show that the scientists thought the creation of an atomic weapon was a pipe - dream , and untenable . Although they could conceivably have been first to generate a man - made fission reaction , in reality they lacked the ambition , the funding , the engineering capability , the leadership , and ultimately , the capability to do so . The undertaking would be of an unimaginable scale , and the resources required to engineer for such use as a nuclear bomb , and nuclear power were deemed too great to pursue . The United States , in collaboration with the British and Canada , correctly recognized the significance of an atomic bomb at the urging of Albert Einstein and Leo Szilard , and immediately embarked upon a race to acquire a usable device . During the quest to create the atomic bomb it is estimated that $ 2 billion , eighty - six thousand tons of silver , and twenty - four thousand skilled workers drove the research and development phase of the project . Those skilled workers included the people to maintain and operate the machinery necessary for research . The largest Allied facility had five hundred scientists working on the project as well as a team of fifty to derive the equations for the cascade of neutrons required to drive the reaction . The state of a fledgling Soviet program was quite different , and the program consisted of fifty scientists , and a mere two mathematicians trying to work out the equations for the particle cascade . The research and development of techniques to produce sufficiently enriched uranium and plutonium were beyond the scope and efforts of the team . The knowledge of techniques and strategies that were being employed in the Allied programs that the Soviet Union procured intelligence on by means of espionage might have played a role in the rapid development of the Soviet bomb after the war . The research and development of methods suitable for doping and separating the highly reactive isotopes needed to create the pay load for a nuclear warhead took years , and consumed vast amount of resources . The Allies of the United States and Great Britain dedicated their best scientists to this cause and constructed three plants , each with a different isotope extraction method . The Allied program decided to use a gas phase extraction to obtain the pure uranium necessary for an atomic detonation . To find this method it took large quantities of uranium ore and other rare materials such as graphite to successfully purify the U - 235 isotope . The quantities required for the development were also beyond the scope and purview of the Soviet program . The Soviet Union did not even have natural uranium ore mines at the start of the nuclear arms race . A lack of materials made it very difficult to conduct novel research , and map out a clear pathway to achieving the fuel they needed . Efforts to produce Uranium fuel dirt cheap only frustrated Soviet efforts , and they found their industrial techniques for refinement lacking . The problem was eventually rectified through the use of information stolen from the Manhattan Project . Without such , the problems the Soviet atomic team experienced would have taken many , many years to correct , affecting the end date of a Soviet atomic weapon significantly . The missing link that explains the great leaps in the Soviets Union ' s atomic program is the espionage information and technical data Moscow was able to obtain from the Manhattan Project . Upon the realization of the American plans to develop an atomic bomb during the 1930s , Moscow began actively seeking agents to get information . Moscow was very specific in asking for information from their intelligence cells in America and demanded updates on the progress of the Allied project . Moscow was also greatly concerned with the procedures being used for U - 235 separation , what method of detonation was being used , and what industrial equipment was being used for these techniques . To obtain this information from the Manhattan Project , the Soviet Union needed spies that , first of all , had security clearance high enough to have access to classified information , and secondly , could understand and interpret what they were stealing . Moscow also needed reliable spies who believed in the communist cause and would provide accurate information . One such Soviet spy was Theodore Hall , who had been a developer on the bombs dropped in Japan . Hall gave up the specifications of the bomb dropped on Nagasaki . This information allowed the Soviet scientists a firsthand look at the successful set up of an atomic weapon built by the Allied team . Although Hall ' s information was helpful to the Soviet cause , the most influential of the atomic spies was Klaus Fuchs . Klaus was a German - born British physicist who was sent to America to work on the atomic project where he became one of the lead scientists . Klaus became a member of the Communist Party while he was still a student in Germany . At the onset of World War II , Klaus fled to Great Britain to escape the fighting , where he became one of the lead nuclear physicists in the British program and was later sent to collaborate on the Manhattan Project . Due to Fuchs ' s position in the atomic program , he had access to most , if not all , of the material Moscow desired . Klaus was also able to interpret and understand the information he was stealing , which made him an invaluable resource . Klaus provided the Soviets with detailed information on the gas phase separation process . He also provided specifications for the pay load , calculations and relationships for setting of the fission reaction , and schematics for labs producing weapons grade isotopes . This information helped the smaller under - manned and under - supplied Soviet scientists with a hard push in the direction of the successful detonation of a nuclear weapon . The Soviet nuclear program would have eventually been able to develop a nuclear weapon without the aid of espionage . But a basic understanding of the usefulness of an atomic weapon , the sheer resources , and the talent weren ' t present until much , much later . The information passed helped the Soviet scientists identify which methods worked and prevented wasting valuable resources on techniques proven ineffective in the development of the American bomb . The speed at which the Soviet nuclear program achieved a working bomb with so few resources was driven by the amount of information acquired through espionage . During the Cold War trials it was touted as one of the most significant intelligence coups in the history of man .