Duck & Cover

After nuclear weapons were developed (the first having been developed during the Manhattan Project during World War II), it was realized what kind of danger they posed. The United States held a nuclear monopoly from the end of World War II until 1949, when the Soviets detonated their first nuclear device.
This signaled the beginning of the nuclear stage of the Cold War, and as a result, strategies for survival were thought out. Fallout shelters, both private and public, were built, but the government still viewed it as necessary to explain to citizens both the danger of the atomic (and later, hydrogen) bombs, and to give them some sort of training so that they would be prepared to act in the event of a nuclear strike.

Source: Wikipedia