The first employment of policemen and every police officer shall be for a probationary term of six months, after which the chief may at his discretion extend the probationary period for an additional term of six months, but no longer. During said probationary period the chief may at his discretion or at the direction of the police board discontinue their services at any time. Having served at least six months’ probationary service to the satisfaction of the board and the chief, such policemen and police officers shall be appointed to the police force of said city and shall thereafter be subject to discharge or removal only for cause and upon complaint being made or charges being preferred against them, a copy of which complaint or charges setting forth the ground thereof shall be given to such policemen or police officers, not less than forty-eight hours prior to the time the complaints or charges are to be heard by the board, and they shall have the right to appear before the board at a public hearing to be held within fifteen days after the filing of such complaint or charges, and be confronted by the witnesses against them and to be defended by counsel and the board after hearing the charges shall take a vote of yeas and nays to be entered upon the records whether or not the charges have been sustained and what punishment, if any, shall be imposed. If the charges are found by the board to be sustained by the evidence, the board may remove such policemen or police officers, or the board may, instead of removal, suspend, reprimand or impose a fine upon the policemen or police officers, and in any case any fine so imposed is not paid the same shall be deducted from the salary of such policemen or police officers. If complaint is made or charges preferred against a policeman or police officer which, in the opinion of the board, does not constitute an offense of which the board shall take cognizance, the board shall dismiss such complaint or charges. The board shall report all decisions on any such complaint or charges in writing to the chief of police and to the officer or policeman. Each decision of the police board in such cases shall be final and not subject to review by any court.