(a) Any employee who leaves the service of any political subdivision for the purpose of entering the armed forces of the United States shall be reinstated in his former position and duties, provided he shall make application for return to such service within ninety days after he has received a certificate of satisfactory service from the armed forces. The appointing authority of any political subdivision in which such employee is reinstated shall certify in writing that such employee is able and qualified to perform the work required and that there is work available for him. In considering the factor of availability of work, the political subdivision shall replace by the returning employee any employee, junior in service, who was employed for the purpose of filling the position vacated by such returning employee. Any employee returning to the service of any political subdivision as herein provided shall be credited, under the provisions of this section, with the period of such service in said armed forces to the same extent as though it had been a part of the term of service to such political subdivision. This section shall not apply to any employee of a political subdivision for a period of more than three years in addition to war service or compulsory service and the ninety-day period hereinbefore provided for.

(b) For purposes of this section, “political subdivision” shall include any town, city, borough, district, school board, board of education, public social service or public welfare agency, public corporation, housing authority, redevelopment or urban renewal board or commission, or other public authority or public agency established by law.