one crucial fact must be kept in mind: none of the roughly seventy thousand nuclear weapons built by the United States since 1945 has ever detonated inadvertently or without proper authorization. The technological and administrative controls on those weapons have worked, however imperfectly at times--and countless people, military and civilian, deserve credit for that remarkable achievement. Had a single weapon been stolen or detonated, America's command-and-control system would still have attained a success rate of 99.99857 percent. But nuclear weapons are the most dangerous technology ever invented. Anything less than 100 percent control of them, anything less than perfect safety and security, would be unacceptable. And if this book has any message to preach, it is that human beings are imperfect.