The police rank structure in the US is not consistant from agency to agency. In most other countries a strict military rank structure is followed. Here we start out at the basic Officer/deputy. Next step is usually Cpl or Sgt., LT, Capt, perhaps CMDR then Deputy Chief, then Chief or Sheriff. The last being an elected position. These promotions are generally based on experience/education or some variation of the above. They do not however correspond directly to military rank. In some agencies a Police sgt may be the second in command, in others he is the first line supervisor with only limited command authority or may fall somewhere in the middle. The basic title of Officer however connotes that policemen are not expected to be automotons but should excersize independant thought and initiative based upon the situation at hand without having so seek higher authority. This is less the case in larger agencies with broad and more militaristic command structures. I suppose this could all be simplified with a national police force, but then again thats not what we really want, is it?