Bomb Shelter (Civ4)/Civilopedia

A bomb shelter is a structure designed to protect the people inside from falling bombs. Today's bomb shelters are designed to shield one from the destruction of a nuclear attack. People have constructed bomb shelters since the first artillery piece was put into action. Sometimes these are rude caves dug in a hillside; sometimes they are elaborate and complicated affairs, self-sustaining for weeks, dug hundreds of feet below the surface.
In the 1950s during the Cold War, American citizens began constructing bomb shelters in their back yards and basements, hoping to avoid destruction during the atomic war they were sure was coming. The US government embarked on an ambitious program to create large bomb shelters in all major cities, stocking them with food, water, blankets, and other essential supplies. These are mostly abandoned today, probably because of the realization that most of them are not strong enough to do much good in the event of a nuclear attack.