>> it's a matter of time. we have to assume the capability exists to attack the united states. >> dirty minutes. that's how long it would take an enter -- an intercontinental missile to reach los angeles. "an american first strike would likely trigger one of the worst mass killings in human history." >> over 10,000 artillery tubes and 20 million people living in seoul. besides conventional, there is chemical, biological, nuclear. a lot of weapons are in covert facilities. >> the nukes are mobile and hard to track. underground bunkers make wiping out weapons nearly impossible. 28,500 american troops are stationed in korea with another