I have a friend who's father had one built in the backyard here in Tampa in the early 60's. She said he stocked it with food and he had a revolver. She said it was not for defense but to use on themselves if needed. They guy was a pretty well respected doctor.
My father told me during the Cuban missile crisis he knew of several people that build them. Other families just picked up and moved. It was pretty serious stuff in Florida during that time.
BTW I found that picture on this site....
ATOMIC-ANNIHILATION