THE ATOM: Five Hundred Hiroshimas

At dawn on March 1, a Marine corporal on lonely Kwajalein saw an awesome sight. "All of a sudden," he wrote his mother, "the sky lighted up, a bright orange, and remained that way for what seemed like a couple of minutes . . . We heard very loud rumblings that sounded like thunder. Then the whole barracks began shaking as if there had been an earthquake. This was followed by a very high wind." In another letter, two days later, the corporal reported that two U.S. destroyers pulled into Kwajalein with victims of atomic radiation.

Man's Greatest Explosion. What the...