So it seems to me that one of the easiest and most effective way to deploy nuclear weapons would be not with a missile that shoots into space before coming back down halfway across the world, but to simply smuggle your nuclear weapons into enemy territory and have them waiting there ready to set off. Now that missile defense is becoming a reality, this is almost a necessity, and the vast amount of international trade all countries do with each other at this point and the small size of nuclear warheads would make it very easy. With this tactic you could even do a preemptive nuclear strike that would destroy most of your opponents nuclear weapons before they even get a chance to fire them assuming you know where most of them are. Then you just have to worry about the ones on subs or in locations you couldn't discover or couldn't smuggle a nuke into. With decent missile defense it would be possible to completely win a nuclear war taking very little casualties using these tactics. Do you think there are hidden nukes already deployed around the major cities of the world in nuclear enabled countries that were smuggled there by hostile forces? If there are, obviously it would be difficult to guard them well, secrecy would be your only safeguard against them being stolen. But what if that fails? What if some hacker finds the location? It could lead to terrorists getting their hands on nukes.