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"  Hardened Artillery Sites (HARTS) HARTS are a chief means of defense in North Korea. The North Koreans bury their weaponry\u2014likely including artillery, anti-aircraft weapons, SCUD missiles tipped with chemical weapons and even airplanes under hills and mountains for protection. In this age of space and drone surveillance, the ability to deliver explosives to major South Korean cities is crucial to North Korea&amp;#039;s plans. There are rings of HARTs past the DMZ. The good news: anything hidden in a hardened bunker must come out to shoot, and there are plenty of South Korean and American eyes peeled for these targets of opportunity.  Here&amp;#039;s a good primer on HARTS, even though it&amp;#039;s from the 1980s.  Northern Limit Line (NLL) When North Korea wants to stir up trouble, it usually looks to the disputed western border in the Yellow Sea called the Norther Limit Line, or NLL, 75 miles west of Seoul. When the 1953 ceasefire was signed that ended the Korean war, the paperwork never specified sea borders. (They were leaving that for a peace treaty that never came.) United Nations commanders established the NLL without North Korean input. That opened the door to conflict\u2014and in 1973 the North Koreans made first claim on the territory. In the 1990s North Korea upgraded its 100 mm coastal artillery batteries with longer-range 122mm and 130mm guns so it could shoot at islands and ships in the area.  The region is a geopolitical football, ready to inflame tensions with an incident. Yeonpyeongdo Island, the target of the shells that ignited this latest crisis, sits squarely in this zone. The warship Chosun was also sunk in this region earlier this year, killing 46 South Korean seamen. Short of all-out war, this area is the likely flashpoint of further acts of aggression, up to an invasion of the islands. The key here is that blood can be spilled away from the mainland DMZ, making it easier to contain. North Korea wants concessions, not an all-out invasion. So this zone is a convenient place to make trouble and control the level of escalation.  The Tripwire Effect There is about 40,000 U.S. troops in South Korea. One reason they are there is for their deterrent value\u2014any war in the mainland will involve the United States, without a doubt. So the soldiers, Marines and airmen there are a human tripwire\u2014a guarantee that the United States will help its ally on the frontlines. The numbers of U.S. troops is rather humble, considering the potential million-man army in the North. Moving these troops around can send messages to North Korea\u2014as well as South Korea. Moving them from the DMZ, for example, could send a signal to the South Koreans to handle more hard diplomacy themselves, just as any increase could signal renewed commitment to an ally.  Strategic Patience This is the stated policy of the United States government towards North Korea. The pattern of diplomacy for several administrations has been to approach North Korea with concessions after they provoke a crisis. This encourages disruptive behavior. But ignoring these tantrums has its risks, as we are seeing, because it encourages the North Koreans to escalate their violent behavior to get the concessions from Seoul and Washington D.C. Also, when an act of aggression does not garner a response, the perpetrating regime could see it as a sign of weakness or a lack of resolve from the victims, and push harder. There is another way to see this calculation, however. North Korea may be too weak to handle a powerful response. A collapsed North Korean government could lead to massive movement of refugees, starvation, civil war and even the use of weapons of mass destruction against South Korea. There is a limit to how much the U.S. and South Korea can destabilize North Korea. Regime change could be the worse case scenario, if there are no plans for dealing with the consequences. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/military/a11850/north-korea-conflict-primer/>