Which war-related experience does not seem to increase the risk of a stress reaction?

I believe the answer is multiple deployments

multiple deployments refers to the millitary personels who were assigned to the battlefield more than one round of millitary assignments.

For the first timers, the rookies tend to haven't realized cold hart truth about the horror that one might experience in the battlefield.

These people would develop higher level of stress for the next assignments because they already realize the worst case situation that they might have to face.