In the French navy they are known by strips of worsted worn in the same place, like those designating the Sergeants and Corporals in the army.
Thus it will be seen, that the dinner-table is the criterion of rank in our man-of-war world.

The Commodore dines alone, because he is the only man of his rank in the ship.

So too with the Captain; and the Ward-room officers, warrant officers, midshipmen, the master-at-arms' mess, and the common seamen;--all of them, respectively, dine together, because they are, respectively, on a footing of equality..