Nuclear weapons CAN be self defense weapons, if you stop watching crappy Hollywood movies, and understand that they are not just for vaporizing cities.
There are two uses for nukes: Counterforce, and countervalue. A countervalue strike is where you go after the things of a country that are valuable in an economic sense: In other words, cities, power plants, harbors, etc.
Counterforce is where you strike at the oppositions nuclear forces, including command and control targets like Presidential Emergency Facilities (including the one at Raven Rock Mountain- believed to be the "Undisclosed Location" that VP Cheney disappears to), Cheyenne Mountain, etc.
Since many of these targets are hardened against a near miss by nuclear weapons, precise targeting is needed to destroy these facilities. Each silo must be hit inorder to destroy it. This takes hundreds of weapons.
The CEP (the accuracy) of submarine launched missiles is too large, the missiles too inaccurate to do that job. Air launched weapons, including bombs, are easy to defend against by simply shooting down the aircraft carrying them. Land based ICBMS are usually the ones that are used as counterforce weapons, because of their accuracy.
Since I do not think that this country is stupid enough to be defenseless, I am assuming that there is another delivery system available, perhaps a classified one, that is taking over the job.