The rating in the Navy is the combination of paygrade and specialty. E-1 through E-6 are junior enlisted members of the Navy, E-7 through E-9 are the senior Non Commissioned Officers or Enlisted and depending upon the specialty wear an insignia of that specialty, i.e. Gunner's Mate - Crossed cannons, Machinist Mate, a ship's propeller. When the person (character) of the Chief of the Boat (actual term on a submarine) is addressed as Chief of the Boat that person is in reality the highest rated senior non commissioned officer on the submarine and is that rating of Master Chief Petty Officer, not only does that person hold that position but is fully qualified in whatever specialty knowledge gained in their Navy career. The Chief of the Boat is the same as with any other Navy vessel or shore station which is that of Command Master Chief. This fully qualified person serves as an advisor to the ship's commanding officer (commissioned) and often serves to be the advocate of the entire enlisted crew and has no command authority whatsoever, only serving at the orders of usually the commanding officer. In no way, shape, or form does the Chief of the Boat, as depicted in this series, ever question the authority of any commissioned officer for any reason although the age difference may be years apart, as command does not count age differences. Also in the first episode I heard the Lt. address the Chief of the Boat as COB although I have never served on submarines, only surface craft and shore bases, I cannot believe that term got past the producers for accuracy in terms, but that's Hollywood ! Show less «