In World War II, one-third of all casualties were psychiatric. …

In Vietnam the official psychiatric casualty rate was less than 5 percent. …The official diagnostic manual of the time did not even have a category for what prior generations had called “shell shock” or “combat neurosis” and the next generation would call “post-traumatic stress disorder.” Men broken by combat did not exist–they had been theoretically and administratively ruled out.
–Jonathan Shay, Achilles in Vietnam–real commentary on this coming soon