the demilitarized zones. here's ian lee in south korea. >> reporter: a war in korea could start like this. volley after volley of north korean artillery raining down on seoul. thousands of weapons are currently pointed at the south korean capital, home to more than 10 million people, defending it is priority number one for her generals and politicians. the u.s. army granted cnn exclusive access to the sixth battalion 37th field artillery, the unit's workhorse, the m-270 alpha 1, also known as steel rain. here's a tour of the multiple rocket launch system. >> being able to provide support fires in an extremely timely