The particular conditions in Vietnam — the guerrilla tactics of the enemy, the conduct of fighting all over South Vietnam, and the mountains and dense jungles with limited landing areas — put a premium on helicopters’ mobility and maneuverability. In addition to transporting troops and artillery, performing reconnaissance, picking up downed pilots, and evacuating the dead and wounded, helicopters mounted with machine guns and grenade launchers also served as attack vehicles. © Bettmann/Corbis.