1. All persons who become policemen and all policemen who enter or reenter the service of the said cities after the date the retirement system begins operation shall become members as a condition of their employment and shall receive no pension or retirement allowance from any other pension or retirement system supported wholly or in part by the said cities or the state of Missouri, nor shall they be required to make contributions under any other pension or retirement system of the said cities or the state of Missouri, anything to the contrary notwithstanding.

2. All policemen in service on the date as of which the retirement system becomes operative shall become members as of that date unless prior thereto any such policeman shall file with the board of trustees, on a form prescribed by such board, a notice of his election not to become a member of the retirement system and a duly executed waiver of all present and prospective benefits which would otherwise inure to him on account of his participation in the retirement system.

3. Any policeman whose membership is contingent on his own election and who elects not to become a member may thereafter revoke such election and become a member, but no such policeman shall receive credit for prior service unless he becomes a member within one year from the date the retirement system becomes operative.

4. Should any member in any period of five consecutive years after last becoming a member be absent from service for more than four years, or should he withdraw his accumulated contributions or should he become a beneficiary or die, he shall thereupon cease to be a member; except in the case of a member who shall have served in the Armed Forces of the United States and shall have subsequently been reinstated as a policeman.