Senator John Kerrys presidential campaign, naturally enough, brought attention to his Vietnam military service. While in Vietnam (from December '68 to April '69), Kerry commanded a river patrol boat in the Mekong Delta. He was wounded three times and won a Silver and Bronze star for his combat activities. Because of his wounds, he requested and received three Purple Heart medals and invoked Navy rule 1300.39 to get sent home early. The 1300.39 rule stated that an officer receiving two wounds that required hospitalization, or three wounds of any severity, could request a reassignment, which "will be determined after consideration of his physical classification for duty and on an individual basis." At the time, these requests were usually granted, and the officer was allowed to leave Vietnam early. The marines had a similar rule, used during the battle for Khe Shan in early 1968. For several months, the marine base of Khe Shan was under siege, and heavy fire. The marines established a policy whereby anyone who was lightly wounded three times, got to leave the embattled base. Naturally, any marine that was seriously wounded got evacuated to a hospital. 

During the Vietnam war, American troops were wounded 352,000 times. But 43 percent of those were "light wounds," that were typically treated within the unit, and often the soldier went right back to work. All three of Kerrys wounds were of this sort, although one of them required that he take it easy for two days. Some 13 percent of the wounds were fatal, often instantly. Another 21 percent were serious, and left the soldier permanently disabled. But 23 percent were serious wounds that eventually healed with no permanent damage. Most of these were what troops called "Million Dollar Wounds." That means you were banged up badly enough to get sent home, but not permanently hurt. 

The navy policy of turning three light wounds into a "Million Dollar Wound" can be traced to similar policies developed during World War II to avoid serious morale problems. The air war in Europe turned out to be quite bloody, and aircrews soon did the math and calculated that they had a near zero chance of surviving if they kept flying bombing missions over Nazi occupied Europe. So the brass established a system where, once a man had flown a number of missions that gave him a 50 percent chance of surviving, he would be transferred to a less lethal job (often as instructors for new aircrews). No such policy was adapted for infantry troops, even though their job was nearly as lethal, in the long run, as was being in a bomber crew. But the infantryman's chances varied considerably depending on which division he was in. Moreover, the infantry had already established informal policies that got men out of action before they went mad from the stress. The navy had nothing as lethal as the heavy bomber missions, although service in submarines were a high risk job. Submarine crewmen were watched carefully for the effects of stress from two many combat cruises.

When the Korean War came along in 1950, the public uproar over reservists (many of whom were World War II veterans) being called up to fight in another long war led to another new policy. This was the "13 month tour of duty." In past wars, you were "in for the duration" (until victory, your death, or a Million Dollar Wound.) Rather than just apply the 13th month rule to combat troops, it was applied to everyone. The rule was revived during the Vietnam war, and, as we see with the navy's "three wound" policy, there were additional ways for a hard hit combat veteran to get cut some slack. 

While these policies to limit combat exposure were popular, they did not appeal to everyone. In the infantry, especially elite infantry units (about ten percent of the total), it was not unusual for troops to volunteer to stay in for Vietnam for two or three tours. Moreover, men in infantry units develop strong personal bonds with each other, and are often eager to get back to their buddies after being wounded. There's a strong sense of mutual obligation among combat troops that produces this reaction. But the average soldier would take any opportunity to get out of combat. Most troops counted the days until their 13 month tour was up. At Khe Shan, marines who got the three wounds could leave without losing the respect of their buddies, although it was considered bad form to put in for a Purple Heart medal for each of those three light wounds. Among combat troops, one Purple Heart per war or campaign was considered sufficient, and many light wounds were never turned into Purple Hearts. One famous Bill Mauldin "Willie and Joe" World War II cartoon shows a ragged GI with a light wound standing in front of a table, behind which a medic offers him a Purple Heart. The GI says, "I already got one, can I have a couple of Asperin instead?"