N.D. Cent. Code § 37-07-02

Re-enlistments in the national guard subsequent to original enlistments may be made for such period as may be prescribed by the adjutant general in accordance with regulations promulgated by the United States department of defense. For the purpose of this section, any enlistment by a person who has previously served six months or more in the armed forces of the United States must be considered a re-enlistment.