Did you know Hitler saved us from an alien invasion, and had to sacrifice his life and reputation by making up the holocaust to keep the whole thing secret ? Murphy will gladly tell you about it, he know everything and he's the only one !
He joined the army for no other reason than staying away from civilization and being well equipped when society inevitably collapses.
He's a pretty efficient flamethrower unit, along with an excellent combat medic. you can count on him to remove those nanomachines in your blood veins.