The years or fractional parts of years that a member serves or has served on active duty in the military service of the Armed Forces of the United States, the United States Merchant Marine or the United States Coast Guard, voluntarily or involuntarily and honorably or under honorable conditions, prior to first and initial employment with the city fire department shall be added to his years of credited service provided that:

(1)     The member contributes to the fund the sum that he would have contributed, based on his salary and the member contribution rate in effect at the time that the credited service is requested, had he been a member of the system for the years or fractional parts of years for which he is requesting credit plus amounts actuarially determined such that the crediting of service does not result in any cost to the fund plus payment of costs for all professional services rendered to the board in connection with the purchase of years of credited service.

(2)     Multiple requests to purchase credited service pursuant to this section may be made at any time prior to retirement.

(3)     Payment by the member of the required amount shall be made within six (6) months of his request for credit, but not later than the retirement date, and shall be made in one lump sum payment upon receipt of which credited service shall be given.

(4)     The maximum credit under this section shall be four (4) years.

(5)     Credited service purchased pursuant to this section shall not count for vesting or for eligibility for not-in-line of duty disability benefits as provided in section 23-83.