Airborne troops are trained and equipped to go into battle from the air, particularly by parachute. Units in which all members must be parachutists are generally considered airborne regardless of how they are deployed. Principal advantages of airborne operations are surprise, the ability to bypass ground defenses, and speed of movement from assembly areas to distant targets. British and American airborne forces were successfully used in the later stages of World War II, particularly in the Normandy invasion.