I've asked myself the same question, and my own military training involved simulated firefights and things. The only time I ever came close to having to answer the question was when I was also about 15 years old.

We were visiting family back in Ohio, and I was at the mall shopping with my grandmother and cousins. I remember being alone near the back of a small store when gunshots rang out. I remember they seemed louder than loud can be possible. I also remember being so terrified that I didn't think. I just reacted.

Reacting meant hyperventilating and running without conscious thought as fast and as far from the gunshots as my skinny little body would take me.

And this was in the days before mass shootings were part of the popular imagination. So it wasn't reacting to that idea.

I don't know how I would react today, more mature and all that. I hope I never have to find out.

Oh, and it turned out those gunshots came from a blank pistol that some teenager was firing as a joke. I don't think too many people laughed.