All soldiers from cooks, truck drivers, engineers and all the rest are combat trained and if called will fight.
There used to be a commonly used phrased called "operational exhaustion" it's a more accurate description of the more common forms of service ptsd.
Some people are trained to kill people, guys like cooks and truck drivers are trained not to get killed.
When your job is killing, you're just waiting for your chance to start killing people. So basically all of our stress hormone is produced and released while in combat.
When you're a cook, your job 24/7 every waking moment of your job is to anticipate someone trying to kill you. This means you have a constant never ending drip of cortisol/stress hormones, never high enough to be enjoyable but high enough that it completely destroys your nervous system. Not only do you constantly worry about it, you have to make decisions based on when you might get killed. I.e. maybe you gotta take a ride in a humvee to get some goat from some villager. You have to decide between giving the boys a treat and getting killed by an IED. It's that constantly having to weigh every trivial decision against your own life that is just toxic for your nervous system. Stress hormones cause neuroplasticity, stress causes you to learn the correct way of doing things for your own survival. It's straight forward if your job is to hold a gun, you're in war mode when you pull the tricker/hear gunfire etc. When you're a cook you're in war mode driving your minivan to a costco to pick up some hambourgers, you can never turn it off when in Iraq and you can never turn it off in American. Not holding a gun means you lack an on off switch.
There's the myth that the brave people join the infantry vice versa and that's why they aren't effected. It's entirely because of the neurological differences between being predator and prey, it's the nature of what job you're assigned.
Keeping in mind a lot of killers don't seek help because it's not common knowledge that killing is a ton of fun. The media manufactures this narrative that it's all just reluctant combat that is totally unenjoyable unless you're a psychopath.
I hope this thread isn't a dig at the military. It's a big machine and everyone plays a role.
What gets me is this idea you need to be a rambo to get respect. The point is they actually served the country doing garbage jobs. They volunteered to do so. You never know when you sign up if you'll spend half your career getting shot at, or spending your days trapped in the desert sleeping in a tent, because your idiot president's son made some corrupt deal with an oil contractor etc. You go where you're told regardless of circumstances.