Leo Szilard invented the atomic bomb and reactor in 1933 as a more efficient method of transmuting elements. It took another 12 years plus a $2,000,000,000 investment by the US to build the first bombs. A patent for an atomic bomb was awarde â¦ d to Leo Szilard in 1934. That patent is regarded as the invention of the atomic bomb.   He immediately tried to turn the patent over to the British government as a gift.