the threat. nobody wants to see a nuclear war, no one can win it. reporter: but as the war rages on in ukraine a mushroom cloud wouldn t just appear on the horizon. there would be warning these warheads were being deployed. reporter: retired commander andy corbett, captasined submarine, capable of delivering its try dent nuclear missile. how easy would it be for putin to launch a nuclear weapon? the authority to launch must come from putin. although the decision rests with the political leader, the ability to do that doesn t. reporter: the world witnessed the destructive power of american nuclear bombs nearly 80 years ago in japan. corbett believes the one going off in ukraine would be many times larger but doesn t see