Any permanent fireman who was or is a member of this retirement system and who has terminated or terminates his employment in order to enter directly into the armed forces of the United States or other emergency wartime service of the United States shall be entitled to continuous service membership in this system, provided he again becomes a permanent fireman after the termination of his service in the armed forces and without intervening employment elsewhere. Any permanent fireman who is on leave of absence due to illness or injury and whose compensation has been partly or wholly terminated during his period of illness shall be entitled to continuous credit in the computation of his retirement allowance, except that, in case of reimbursement of his contributions to the fund, under the provisions of N.H. Rev. Stat. § 102:19, he shall be entitled to his actual contributions to the fund only, plus interest, as designated by the board.