The officers of the police force in each such city shall be as follows: one chief of police with the rank of colonel; lieutenant colonels, not to exceed five in number and other such ranks and number of members within such ranks as the board from time to time deems necessary. The officers of the police force shall have commissions issued to them by the boards of police commissioners, and those heretofore and those hereafter commissioned shall serve so long as they shall faithfully perform their duties and possess the necessary mental and physical ability, and be subject to removal only for cause after a hearing by the board, who are hereby invested with exclusive jurisdiction in the premises.