Duck and Cover

Overt- The governent wants you to be safe (They are giving you safety precautions against a new danger: the atomic bomb)

Covert- The government can't really prevent the atomic bomb from striking, so they're trying to do their best to protect you, although you're not really safe. (They never mention any ways they can stop the atomic bomb from striking)

This is propaganda because they are trying to make you feel safe without telling you they have no way of stopping a nuclear attack.