A space rocket landed in 1938. No one knew where it came from and nothing in it survived. Still the U.S. Army took cellular samples from the corpse within and experimented with them and by the time World War Two began they added their experimental 'Super-Soldier' formula, hoping to create a champion of liberty. They injected the formula into a 4-F volunteer, known to the general public as Clark Kent, and exposed him to massive jolt of solar radiation. given what they knew of the alien cells, the scientists had some clue as to how this might affect the test subject -Clark Kent- but no one expected him to be granted powers and abilities so beyond those of mortal men. That's how the hero Super-Soldier became what he is today.