"Having been raised where I was, I know and have known a quite large number of commando and special forces folks. *None* of them were violent nut jobs. In order to do what they did, they needed the sort of sanguine calm demeanour you describe for the submariner. I guess your old teacher was the exception."
I grew up around SpecOps people too. And I too would describe them as calm. But I would never ascribe to them the demeanor of a submariner, which is far more akin to that of a soldier in a foxhole. A submariner, like a solider in a foxhole, fights for the man to the left of him, and the man to the right of him. This is not at all what motivates the special forces commando. For that, you need a little bit of Firefly:
The Operative: I'm sorry. If your quarry goes to ground, leave no ground to go to. You should have taken my offer. Or did you think none of this was your fault?
Capt. Malcolm Reynolds: I don't murder children.
The Operative: I do. If I have to.
Capt. Malcolm Reynolds: Why? Do you even know why they sent you?
The Operative: It's not my place to ask. I believe in something greater than myself. A better world. A world without sin.
Capt. Malcolm Reynolds: So me and mine gotta lay down and die... so you can live in your better world?
The Operative: I'm not going to live there. There's no place for me there... any more than there is for you. Malcolm... I'm a monster.What I do is evil. I have no illusions about it, but it must be done.