China's Great Dam

The most priceless jewels in the arsenals of a handful of countries, some nuclear submarines carry more firepower than all the bombs dropped in history. Since the 1950s, these lethal steel sharks have been a cornerstone of American defense policy. The Cold War launched an underwater race for supremacy with the Soviet Union. The result: engineering miracles, which roam 70% of the earth's surface, providing deterrence to enemies, intelligence about adversaries, and an abiding sense of dread.