Days in combat is a factor of PTSD, as Grossman covers in his books.
Watching the troops 24/7 is part of the problem. The troops feel that they are watched because they did something wrong. The current system of “suicide prevention” reinforces the “you have been a bad boy” mental state of the soldiers. Depressing the troops with endless and repeated suicide prevention training is part of the problem too.
BTW: We need to separate the non-combat related suicides from the combat related. Including people who have made poor life choices (cheating on their spouse, stealing, etc) with those who are honorably injured in the war zone is just wrong.
You really need to read Grossman, he basically agrees with your theory. Where he, and I (if I remember the book correctly), disagree with you is on the danger/safety cycle. It is duration in combat (or stress) that hurts. Time away from stress can lower, but not empty, your stress tank.
One thing Grossman does not address is Traumatic Brain Injury (TBI), which is beginning to appear to be a major factor in PTSD.
BTW2: On Killing is basically a revised version of On Combat. On Combat was written with the law enforcement community as an audience. On Killing was written for the military.
Just remembered that one of our old WWII Navy vets stood up at church on Vet’s Day and spoke of his time in service from 41-46. One story he told was of a sailor who couldn’t stand it and killed himself.
That would be one way to get some idea of the incidence of suicide, but it would have to be done immediately given the quickly deceasing members of our WWII era.
One could simply poll them about numbers of suicides they knew of, and at the same time do that for all Korea, Vietnam, etc. Polling the question in today’s force and simultaneously having the actual number of suicides would provide some kind of baseline for comparison.