hans kristensen says he discovered this photo on a u.s. air force website showing the inside of a shelter where nuclear bombs would be loaded aboard american and nato jet fighters. >> kristensen: each vault can have up to four nuclear bombs. they hang right next to each other. it can... it sinks into the >> martin: and just out of a doomsday movie, the nuclear weapon rises out of the floor. >> kristensen: right. >> martin: the bomb is called the b-61, and it's being upgraded by adding a new set of tail fins that give it greater accuracy. that would allow the b-61 to destroy its target using a lower-yield nuclear weapon, which would decrease the number of civilian casualties. the air-launched cruise missile, says major general clark, can also be turned into a low-yield nuclear weapon >> clark: there is a variable- yield option on this weapon, so we can change that yield within the weapon. >> martin: you can dial in a yield? >> clark: that's what we call it, actually, "dial a yield." >> martin: does that make a nuclear weapon easier to use? >