Okla. Stat. tit. 11 § 49-139
Any such person shall be carried on the roll of members of the fire department during such absence and shall be entitled to all advancements, seniority and promotions under the rules, regulations and customs of the fire department, during his said absence, and all advancements and promotions made in the fire department during his absence in such military or naval service to which he would have been entitled shall only be filled temporarily and shall be subject to the rights of such person who shall, within ninety (90) days after he has been honorably discharged or received a certificate as a reserve component of the land or naval services, have the right to make application for reinstatement, and he shall have preference over any and all members of the fire department who have been employed by such municipality subsequent to his entering said military or naval service, and upon such application it shall be the duty of the executive head of the fire department to reinstate such person as an actual member of the fire department with all rights of advancements and promotions, provided, he has not been mentally or physically disabled since last serving in such fire department and is able to pass the usual and customary physical and mental examination then required by the State Board for entry into said fire department, and he shall not thereafter be subject to reduction of compensation or dismissal without just cause.
Okla. Stat. tit. 11, § 49-139