<Tr> <Td> <Ul> <Li> History </Li> <Li> Warfare </Li> <Li> Design </Li> <Li> Testing </Li> <Li> Delivery </Li> <Li> Yield </Li> </Ul> <Ul> <Li> Effects and estimated megadeaths of explosions </Li> </Ul> <Ul> <Li> Winter </Li> <Li> Workers </Li> <Li> Ethics </Li> </Ul> <Ul> <Li> Arsenals </Li> <Li> Arms race </Li> <Li> Espionage </Li> <Li> Proliferation </Li> <Li> Disarmament </Li> <Li> Terrorism </Li> <Li> Opposition </Li> </Ul> </Td> </Tr> <Ul> <Li> History </Li> <Li> Warfare </Li> <Li> Design </Li> <Li> Testing </Li> <Li> Delivery </Li> <Li> Yield </Li> </Ul> <Ul> <Li> Effects and estimated megadeaths of explosions </Li> </Ul> <Li> Effects and estimated megadeaths of explosions </Li>

How many fallout shelters are in the us