They're huge painted numbers and drawings of tanks bearing the North Korean star emblem.

Through a megaphone, a soldier announces what target to watch. A South Korean F-16 fighter jet screams over shortly after, dropping a bomb right on the spot.

Next up we're treated to the impressive sight of an E-737 "Peace Eye," a state-of-the-art surveillance aircraft that can detect movement across most of North Korea's airspace from behind the South Korean border.

We'd been given rare access to a live-fire exercise involving armed forces from South Korea and the United States.

It happened to coincide with the annual military exercise known as "Ulchi Freedom Guardian," a series of mainly computer-simulated drills involving an estimated 80,000 troops. Its aim is to simulate the defense of South Korea from an attack by the North.

From behind us, the roar of anti-aircraft canon shakes the ground beneath us and leaves us coughing through the thick, acrid smoke. It smells like the end of a major fireworks display on New Year's Eve.

"Our soldiers are ready and able," says Battalion Commander Heo Jing-Nyeong, of the South Korean army. "With the will and courage to fight against the enemy."

U.S. Private First Class Israel Corona, part of the American military contingent, tells us, "We're just ready to fight tonight."

(CNN)