Well, it's an act of war to hit SK territory as well. If an American installation is hit, a measured response would still be required. A couple of stray shells wouldn't, and shouldn't, trigger a general conflict. A deliberate and significant targeting of an American installation would be a different matter altogether. I would think that NK doesn't want all out war - they just like to stir sh*t every now and then. They have wing nuts running the country and the regime should've been turfed long ago. Of course, the only reason that hasn't happened is China, of course. They will not tolerate an invasion of - or even large air strikes - on NK. For one, it's in China's interest to have NK keeping everybody off-balance. Plus, they don't want refugees streaming across their border.