China's nuclear arsenal has long been an enigma. The arsenal has historically been small, based almost exclusively on land-based ballistic missiles, maintained at a low level of alert, and married to a no-first-use doctrine - all choices that would seem to invite attack in a crisis. Chinese leaders, when they have spoken about nuclear weapons, have articulated ideas that sound odd to the Western ear. Mao Zedong's oft-quoted remark that 'nuclear weapons are a paper tiger' seems to be bluster or madness.

China's nuclear forces are now too important to remain a mystery. Yet Westerners...