In computing years of service as a district attorney, credit shall be given for services in the armed forces of the United States occasioned by only one of the following national emergencies: World War I, World War II, or the Korean Conflict. Such credit shall be given upon payment into the fund of the maximum payments provided under Code Section 47-12-41 for each year or fraction of a year of such service in the armed forces, together with 6 percent simple interest on such amount for each year from the beginning of his service as a district attorney until the date such contributions are paid into the fund. The district attorney shall receive a credit of one year for each year or fraction of year of such service for which contribution into the fund has been made. Such payment shall be made no later than January 1, 1976.