The contributions of the Soviet espionage were huge in different fields. And this point is in fact a proof that the Soviet system knew the level of its scientists. It didn’t trust them in finding how to create the atomic bomb. With the declassification of Soviet intelligence materials, it became obvious how big the extent of the information obtained by the Soviets from US sources was. The Soviets with their information replicated US success with gaseous diffusion in the uranium isotope separation. The Soviets obtained form Klaus Fuchs the cross-section of D-T fusion. Before that Vitaly Ginzburg and Andrei Sakharov estimated that it should be similar to those of the D-D reaction. Another point which was crucial and attributed to the Soviet espionage is the possibility of using plutonium instead of uranium in a fission weapon. And the extract of plutonium in the uranium pile permitted avoiding the difficult process of uranium separation. All these evidences due to the cryptanalysis but also to the declassification are new data to estimate correctly the soviet scientific level of that time. Quod erat demonstrandum.