Suppose, in a small, nuclear-armed country like Pakistan, the government has a nuclear-weapons capable submarine. This sub is stormed by fighters from a terrorist group . . . . this could even happen while it was at sea. They take over the sub, (as actually was accomplished multiple times during World War II, when the Nazi subs were taken over to get a-hold of the Enigma coding device) and force the people with the technical know-how to fire off the nuclear weapons at whatever country they deem hostile enough to them to warrant it. (It goes without saying who those countries might be.) This type of situation could get serious fast, because the superpowers would be taken by surprise, and would have to decide, within a very short time, (four minutes or so) who fired the nukes, and how to respond . . . . it could go very bad, very quickly. This is just one more reason why nuclear weapons on the planet is a very bad idea.