Australian Navy Captain. In the Australian Navy ranks and many other navies in the world, the Captain is often used rank to design the commander of the largest ships. and is equivalent to the colonel army rank. More precisely, the command of a large ship is assigned to an officer with naval rank between (OF-4) and commodore or rear admiral(OF-6). See the full list below for a complete description of ranks and the abbreviations.
Roles and size of ships. Captains can be assigned to lead and command ships of cruiser size or larger, the more senior the officer, the larger the ship, but ship commanders do not normally hold a higher rank than captain. Depending on navies, the roles may change. For example, in the Royal Navy, captain might command a destroyer flotilla, but in such a case it would be under a specific appointment, rather than a permanent rank.
Senior officers. Large ships such as carriers, or flagships of an entire combat group would be under the command of Rear admirals. The flagship is where the Rear Admiral also embark. however, the ship’s captain will still retain command of ship. So independently of the seniority and presence of senior officer aboard, all orders will be given through the captain of the ship. Note that the rank of captain allows you to have the rank and or your command in both afloat and ashore missions.
Admiral of the Fleet
Acting Sub Lieutenant
In addition, there are other ranks that are not associated to commissioned officers:
Warrant Officer of the Navy and Warrant Officer
Chief Petty Officer