Any person who, in circumstances not amounting to an offence under any other provision of this Code, contrary to his duty or without proper authority alters, adjusts or interferes with any aircraft, motor vehicle, vessel, weapon, machine or instrument used or intended for use by the South African Defence Force or any part or accessory of any such aircraft, motor vehicle, vessel, weapon, machine or instrument shall be guilty of an offence and liable on conviction to imprisonment for a period not exceeding two years.