What does Duty Preference mean?
Duty preference refers to certain things you would prefer while on duty. This can include certain shifts or hours you prefer to work or which area of the field you prefer to work in.
It depends on what you mean. While a marine is on active duty, he can carry a gun if the duty requirements allow it. If you mean can a marine carry a gun when not on duty simply because he is a member of the armed forces, no. Military personel must follow the law of whatever state they are in when they are not on base and off duty.