(a) Vacancies in positions in a paid police department of a Class I or Class II city shall be filled, so far as practicable, by promotions from among individuals holding positions in the next lower grade in the department.
(b) Promotions shall be based upon experience and by written competitive examinations to be provided by the Policemen's Civil Service Commission: Provided, That except for the chief or deputy chiefs of police, if the position of deputy chief of police has been previously created by the city council of that Class I or Class II city, no individual is eligible for promotion from the lower grade to the next higher grade until the individual has completed at least two years of continuous service in the next lower grade in the department immediately prior to the examination: Provided, however, That notwithstanding the provisions of section six of this article, any member of a paid police department of a Class I or Class II city now occupying the office of chief or deputy chief of police of that paid police department, or hereafter appointed to the office of chief or deputy chief of police, except as hereinafter provided in this section, is entitled to all of the rights and benefits of the civil service provisions of this article, except that he or she may be removed from the office of chief or deputy chief of police without cause, and the time spent by the member in the office of chief or deputy chief of police shall be added to the time served by the member during the entire time he or she was a member of that paid police department prior to his or her appointment as chief or deputy chief of police, and shall in all cases of removal, except for removal for good cause, retain the regular rank within that paid police department which he or she held at the time of his or her appointment to the office of chief or deputy chief of police or which he or she has attained during his or her term of service as chief or deputy chief of police.
(c) The provisions of this section apply and inure to the benefit of all individuals who have ever been subject to the provisions of this article. The commission may determine in each instance whether an increase in salary constitutes a promotion.