Albert Einstein, noted by Time Magazine as "Person of the Century," was the first to comprehend that energy and mass (matter) are equivalent. When he wrote his world-changing paper ("Does the Inertia of a Body Depend Upon its Energy Content?"), the 26-year-old patent clerk was so forward-thinking he had no prior sources to cite. His paper, as originally published, was without footnotes.

In a startling departure from prior thinking, Einstein theorized (E=mc2) that matter could become energy (and energy could become matter) under the right circumstances. As he himself explained (follow the link to hear him):

...very small amounts of mass may be converted into a very large amount of energy and vice versa.

Once Einstein’s revolutionary theory was accepted - which did not happen overnight - scientists realized that enormous amounts of energy could be produced from splitting tiny particles of matter - like atoms. (For submarines, such a power source would later transform “boats that dived” into true sub-marine vessels that could remain underwater indefinitely.)