Wouldn't matter if they could use several nukes along the DMZ. North Korea's utter lack of modern armor, and the absurdly dense urban terrain with numerous fixed anti tank barriers along all the (very few, just four really and only two are any good) possible invasion corridors would stop an invasion dead in its tracks. They'd be lucky to advance more then 10km now; and maneuvering through a fallout zone and around nuclear craters is not going to help. An encirclement of Seoul was a threat through the 1970s and 1980s when the ROKA was all light infantry and had no modern tanks or artillery either. But now the ROKA is a much more modern mechanized force... while North Korea's military has gained almost no new equipment at all and what they had in the 1980s was already obsolete. They also just don't have enough fuel or food to use all the forces they have, an attack would have to be carried out with only the best troops greatly reducing the Norths human sea advantage.recon20011 wrote: The North Koreans will probably use chemical or nuclear weapons to blast a hole in the DMZ defenses and clear a path to Seoul, their ace will be capturing Seoul's population alive and using them as a shield against UN NBC retaliation.
Of course, since the North used nukes first, the invasion force would be wiped out within hours anyway. Even if the US nuclear weapons stored in South Korea were lost to a North Korean first strike, nuclear bombers from CONUS could arrive in under a day. Even if all ROK defense collapsed one line after another, the North Koreans would just not be able to drive tanks fast enough down the highways to encircle Seoul before that could happen. Plus the US could always fire ICBMs.
The real invasion risk to the South is about zero now, the ROK doesn't even take that to be the main national threat anymore, which is why they've put so much money into naval and air power recently. This is also a major reason why the Norks are so troublesome, they know they can't threaten invasion anymore and they don't like it, so they feel they MUST have nuclear weapons to restore the balance of terror. Since the nukes aren't working right yet, they've got nothing and that is a very unhappy situation.