1. As an incident to his contract of employment or continued employment, each employee of the highways and transportation commission of Missouri, each uniformed member of the highway patrol, and each civilian or nonuniformed employee of the Missouri state highway patrol shall become a member of the system as established in section 104.020 on November 1, 1955, and every person thereafter becoming an employee in either of the three classifications shall become a member at the time of employment. Each employee’s membership shall continue as long as he shall continue to be an employee; be on leave for military service or training as hereinafter provided; or receive or be eligible to receive an annuity or benefit hereunder.

2. The military service or training must be that to which he shall have become obligated, either irrespective of his consent under the mandatory provisions of law or as a volunteer while the United States is engaged in actual active armed warfare, if within ninety days after becoming eligible for release from said service obligation he shall have reentered the employment of the transportation department or the state highway patrol. No payment of contributions shall be required of such member upon his return from military service, but he shall be given credit for the actual time of military service rendered at the salary received at the time of entry into military service.