the two stand out moments (well one was longer than a moment) for me was finishing high school and enlisting with a half dozen of my friends. we were mostly on the poorer side of middle class, and with expenses on the rise where we lived we knew that even with a scholarship, we couldn't afford to complete college. working part time and attending courses sucks, and after my enlistment i did that and glad i waited until then to do it - as an 18/19 year old i don't think i would have coped too well financially or academically.
a couple of my friends went into different branches, i joined the Army. one of my very good friends (not quite best friend) joined the Air Force. we kept in touch rarely, mostly busy doing military things.
it was during my time in Iraq where moment #1 hit me and it's stayed with me in multiple ways. it was OIF 1, during the push into Baghdad for the Airport. about 2 days into the fighting were were moving northward towards Karbala to support Airborne elements already in the fight. during dismount from our vehicles were were mortared. now, at that point were were constantly getting pot shots or sporadic engagements, meeting with surrendering enemies and capturing abandoned gear, et c. mortars were part of that as well as random RPG fire and none of it was close enough to worry about.
some guy that day finally figured out his trig and started sending reasonably accurate fire on our position. i won't get into the further details of it, but about 12 meters away, while i was pulling myself and another soldier into cover, i watched a man i had trade food and jokes with, bullshit with in vehicles and on patrol with, get destroyed by mortar shrapnel. completely shredded the clothing, but what killed him was shrapnel to the face, neck and legs; and concussive damage that knocked him down and out. by the time we had reorganized a minute later he was gone already - he was just too close to the blast.
that fucked me up enough that i don't fully remember the rest of the engagement other than just going through the motions.
moment #2 was when i finally made it back home and learned that out of my group of friends, only one other made it back home alive.
i don't think i have any lasting trauma about it, no PTSD or anything other than some old injuries and the memories of it all, but sometimes it hits you when you're half expecting an in-joke or something and there's just silence.