"The introduction of the helicopter to the Army Medical Department's traditional battlefield mission of medical evacuation of sick, injured, and wounded soldiers from frontline units to hospitals in the rear had its rudimentary beginnings in World War II. During the Korean War, the helicopter came of age and soon became the primary means for evacuating the most seriously wounded, injured, and ill soldiers from the very fighting front to mobile army surgical hospitals (MASHes) and rear area evacuation hospitals for life-saving treatment.  Helicopter medical evacuation, simply known as MEDEVAC, soon became central to the Army Medical Department's concept of battlefield care and evacuation.  During Vietnam, helicopter MEDEVAC became known as "Dustoff", a designation it has retained ever since..." Digital text of this and other related papers from the U.S. Army Medical Department Office of Medical History at this link.