Any person who unlawfully assaults, fires at or throws any missile at, against or upon any member or body of the National Guard or any civil officer or other person lawfully aiding them, while on active duty in the State or aiding in the enforcement of the laws under proper authority, shall be guilty of a misdemeanor and on conviction shall be liable to imprisonment in the State Penitentiary for a period of not more than two years in the discretion of the court.