Nation: Fire in the Sky

With a brilliant white flash that turned night into day over millions of square miles of the Pacific, the U.S. exploded its highest nuclear test some 260 miles above the earth. It was the first invasion of the fringes of outer space by a thermonuclear device, and what it proved militarily for the security of the U.S. was a carefully kept secret. But the one-megaton bomb that arched over tiny Johnston Island on a three-stage Delta rocket caused the most dazzling—and awesome—display of man's power ever seen.

The test was the most publicized, most debated and most postponed of the U.S. current...