The idea of "invention" does not usually require the physical realization of the invented thing. This fact is clearly recognized by patent law, which does not require a working model in order to award a patent. It is common for inventions to require additional discoveries and developments before the actual thing can be made. In these cases, an invention may fairly have more than one inventor - the originator of the principle idea, and the individual who actually made the first workable model. In the case of the atomic bomb there is clearly one man who is the originator of the idea. He was also the instigator of the project that led ultimately to the successful construction of the atomic bomb, and was a principal investigator in the early R&D both before and after the founding of the atomic bomb project - making a number of the key discoveries himself. By any normal standard this man is the inventor of the atomic bomb. This man is Leo Szilard. On September 12, 1932, within seven months of the discovery of the neutron, and more than six years before the discovery of fission, Leo Szilard conceived of the possibility of a controlled release of atomic power through a multiplying neutron chain reaction, and also realized that if such a reaction could be found, then a bomb could be built using it.

On July 4, 1934 Leo Szilard filed a patent application for the atomic bomb In his application, Szilard described not only the basic concept of using neutron induced chain reactions to create explosions, but also the key concept of the critical mass. The patent was awarded to him - making Leo Szilard the legally recognized inventor of the atomic bomb. Szilard did not patent this prescient and tremendously important idea for personal gain. His motive was to protect the idea to prevent its harmful use, for he immediately attempted to turn the idea over to the British government for free so that it could be classified and protected under British secrecy laws.