N.H. Rev. Stat. § 103:8
In addition to the assessment made on the assessable part of any policeman's annual salary as hereinbefore provided, and subject to the approval of the board and to such rules and regulations as the board may prescribe with respect thereto, any permanent policeman may provide for himself an additional retirement allowance by making special deposits in his individual account. Such special deposits together with interest credited thereon as determined by the board shall be paid to him upon resignation or dismissal from service, or to his estate or his designated beneficiary upon his death before retirement. Upon his retirement for any cause, his accumulated special deposits shall be returnable to him in cash, or, at his election, part or all of such accumulated special deposits may be taken as a monthly annuity of equivalent actuarial value; provided such annuity together with his regular monthly retirement allowance shall not exceed a sum equal to 1/2 his average monthly salary during the 12-month period preceding his retirement.
RSA 103:8
1951, 63:1. 1953, 112:2, eff. Apr. 22, 1953.