Well, they were meant to be protectin' people from the bombs.

[ A beat. ] Uh. Nuclear bombs. Dunno if you have 'em where you came from, but they basically destroyed the entire world. People in Vaults were saved, people outside managed to survive too but lost everything. Or became mutated. Either-or. That was about two hundred years back.

Dunno if Vault-Tec was thinkin' the bombs would actually drop. My own knowledge on them is a bit biased. [ He has an awkward smile. please don't get him talking about his cult worship of them, ]