900,000 allied military personnel and Vietnamese civilians. The Vietnamese, both civilian and military, constituted about one half of the total; U.S. military personnel, about 45 percent; and other non-Vietnamese allied military, about 5 percent. These proportions varied, however, over the course of the war. Before 1965 about 90 percent of the patients were Vietnamese. Then the U.S. buildup began in 1965, and the figure dropped to only 21 percent for 1966. As the United States started to turn over more of the fighting to the South Vietnamese, the number rose until it reached 62 percent in 1970. Unfortunately, exact percentages of wounded, injured, and sick among the air ambulance patients are lacking. Although only about 15 percent of the cases treated by all Army medical personnel in the war were wounded in action, it seems that the percentage of wounded among the air ambulance patients was much higher, between 30 and 35 percent, since the ambulances gave first priority to patients in immediate danger of loss of life or limb, a condition most closely associated with combat wounds. Up to 120,000 of the U.S. Army wounded in action admitted to some medical facility-90 percent of the total-were probably carried on the ambulances. This is about one third of the some 390,000 Army patients that the air ambulances carried to a medical facility.

The widespread use of the air ambulances clearly seems to have reduced the percentage of deaths from wounds that could have been expected if only ground transportation were used. In World War II the percentage of deaths among those Army soldiers admitted to a medical facility was 4.5; in Korea, 2.5. In Vietnam it was 2.6, despite a road network as bad as that in Korea, despite thick jungle and forest that made off-the-road evacuation much more difficult than in Korea, and despite the large numbers of hopeless patients whom the air ambulances brought to medical facilities just before they died. Another statistic-deaths as a percentage of hits-shows more clearly the improvement in medical care: in World War II it was 29.3 percent; in Korea, 26.3 percent; and in Vietnam, only 19 percent. Helicopter evacuation was only one aspect of the Army's medical care in Vietnam, but without that link between the battlefield and the superbly staffed and equipped hospitals, it seems likely that the death rate would have surpassed perhaps even that in World War II.

Measured both by the patients moved and the number of missions flown, the air ambulances were busiest in 1969, when by the end of the year 140 were stationed around the country. Over the course of the war the divisional air ambulances of the lst Cavalry and 101st Airborne constituted only 15 percent of the total. Because of the high maintenance demands of the UH-1, only about 75 percent of the ambulances were flyable at any given moment, although replacement aircraft could sometimes be borrowed from helicopter maintenance