Way back when, during Sub School, I had the 8-midnight watch at the Badge and Pass office at New London. When it slowed down, I was back talking to the Duty Officer when we heard a shot from just outside. Two Marines were playing quick-draw in the guard shack, and one shot the other at point-blank range. The bullet scrambled his insides, and never came out. The shooter was convicted at Court-Martial (I assume voluntary manslaughter).
Marine guards. Man, that *was* a long time ago. I don't remember any accidental discharges on any of my boats (since the weapons were unloaded), but I do remember them falling into the river with alarming consistency along with the occasional lost shell.