N.H. Rev. Stat. Ann. § 103:12

Any permanent policeman who accepts the provisions of this chapter may retire from active service after serving as a permanent policeman for a period of 25 continuous years or after reaching the age of 65 regardless of his period of service as a permanent policeman. Any permanent policeman accepting the provisions hereof who shall be dismissed from service after having served as a permanent policeman for a period of 25 continuous years, or after reaching the age of 65 regardless of his period of service as a permanent policeman, shall be entitled to the benefits of this chapter. Upon retirement a permanent policeman shall no longer be obligated to pay assessments to the retirement fund. The board may, if it deems proper, in a case of a break in a policeman's continuous service of not more than 3 years, construe as a period of continuous service of such policeman, by adding his service before the break to his service after the break.