Soldier Watching Teargas Explosion

(Original Caption) An Khe, South Vietnam: A trooper of the US First Cavalry waits, his rifle at the ready, to see if the teargas thrown into a Viet Cong tunnel will flush anything. In this instance, the tunnel was empty. The troopers, operating in heavily-Communist fortified areas of the central highlands, are making regular use of the teargas in an effort to save noncombatants who are often located in Viet Cong areas.