Every member of the classified service of the fire or police department of any municipality coming under the provisions of this Division 2.1 who was engaged in a military or naval service of the United States at anytime for a period of one year, and who was honorably discharged therefrom, who is now or who may hereafter be on inactive or reserve duty in such military or naval service, not including, however, persons who were convicted by court-martial of disobedience of orders where such disobedience consisted in the refusal to perform military service on the ground of alleged religious or conscientious objections against war, and whose name appears on existing promotional eligibility registers or any promotional eligibility register that may hereafter be created as provided for by this Division 2.1 shall be preferred for promotional appointments of the fire or police department of any municipality coming under the provisions of this Division 2.1.