Any employee of a city having an employees’ pension fund who resigns therefrom or who has been granted or shall be granted a leave of absence to serve in the armed forces of the United States or armed forces reserve thereof, or who shall have been selected for training under the selective service provisions of the laws of the United States, and who has returned to the employ of the city with an honorable discharge from, or other documents showing honorable service in, such service, shall have the period of such service included as part of the employee’s period of service to such city.