Poncheon, South Korea (CNN) -- Heavy gunfire breaks the silence in this valley of South Korea. Stryker combat vehicles speed towards a distant target ... their machine guns focused on the enemy beyond.
Infantry fan out into the surrounding hills, still partially covered with snow. Blue skies and bright sunshine are not enough to warm this part of the Korean peninsula much above zero degrees Celsius.
The enemy today is imagined, but the threat is very real. This military drill is no more than 15 kilometers away from the demilitarized zone separating South and North Korea.
This is just one part of the joint annual U.S.-South Korean military exercises that the U.S. insists are defensive in nature. But North Korea disagrees. Pyongyang has called the drills a provocation and has threatened to "engulf Seoul in a sea of flames." North Korea has often claimed it sees these drills as preparations to invade North Korea and topple Kim Jong-Il's regime.
Colonel Ross Davidson, Commander of the First Heavy Brigade Combat Team in South Korea, tells CNN, "While some would make the argument it's a provocation, you could just as easily argue it is in fact a deterrent and also a partnership that's between the Republic of Korea and the United States." He adds that the South Korean-U.S. relationship is "one of the strongest alliances in the modern era."
It was during a South Korean live-fire military drill last November that North Korea shelled Yeongpyeong island, killing two South Korean marines and two civilians. Tensions have been high ever since. Working-level military talks between the two Koreas failed last month after two days.
These joint drills are also preparing for any unconventional attacks. The two militaries showcased their ability to withstand chemical, biological and nuclear attacks to the media last week. Brigadier General Chuck Taylor said, "The North Koreans have threatened to use weapons of mass destruction. These exercises help us to deter based upon our readiness and if deterrence fails, to help us prevail in any kind of threat environment."
The Strykers used for Monday's live fire exercises and some of the troops were flown from Fort Lewis in Washington State in the U.S. They're part of a contingency platoon which means if tensions on the Korean peninsula escalate, they can be deployed here immediately.
The U.S. military says these kinds of drills can prepare these soldiers for any conflict in the world, but training on this particular terrain can only help if they're ever called upon.