N.H. Rev. Stat. Ann. § 261:41

The provisions of this chapter relative to the registration of vehicles and the display of number plates shall not apply to vehicles having registration and displaying plates issued by the armed forces of the United States for vehicles owned by military personnel, but such exemption shall be valid only for a period of 7 days after the owner thereof has entered this state for the purpose of traveling to either his place of residence or a point of military duty.