53 Pa. Stat. § 23611
Members of the fund shall be eligible to pension under said fund upon written application of such member, stating his desire to withdraw from service in said city, which application shall show that such employe has rendered at least twenty years service to the said city, at least one year of which was immediately prior to his application, but which does not otherwise necessitate continuous service but that such service shall total twenty years and shall include service in the armed forces of the United States or active service in the Pennsylvania State Militia when said militia has been mobilized for internal police duty whether such armed forces or militia service occurs prior to or during such city service not to exceed three years. Each member desiring such credit shall be required to pay to the fund an amount equal to five per centum of the salary or wages he or she would have earned had he or she been a member of the bureau of fire during the period of military service, with interest at the rate of five per centum of the amount paid into the fund.
53 P.S. § 23611