Invented by Jean Bernard Leon Foucault in 1852 as an independent method for demonstrating the earth's rotation, the gyroscope has become one of the most useful scientific instruments. In the century and a half since its invention, the gyroscope's history has become inseparable from the history of growing military and commercial needs of the world's great power. At the height of the Cold War, American and Soviet gyroscopes were fundamental components of inertial guidance systems for submarines, missiles, and aircraft, systems that guaranteed the retaliatory Armageddon that lay at the core of the doctrine of Mutual Assured Destruction. In a sense, gyroscopes helped keep the long, cold peace.