Chief of the Boat (COB) is an enlisted sailor on board a U.S. Navy submarine or Cyclone Class Coastal Patrol Ships, who serves as the senior enlisted advisor to the commanding officer and executive officer, and assists with matters regarding the good order and discipline of the crew. The Chief of the Boat is the equivalent of a Command Master Chief in shore and surface units. There is only one COB on a submarine or Coastal Patrol Ship and he is generally responsible for the day-to-day operations of the non-nuclear portion of the boat, and the morale and the training of the boat's enlisted personnel. The COB is typically the most senior enlisted man; however, the commanding officer is neither required to select the highest ranking sailor nor the most senior in grade or time aboard. Likewise, the COB is not necessarily replaced when a more senior sailor reports aboard.
The selection process for a COB starts with the commanding officer's recommendation, which goes to the Naval Military Personnel Command via the Squadron Commander. Nominees are interviewed by other COBs.
When a new enlisted sailor joins a boat's crew, the COB is usually one of the first people the new sailor will meet. Although the role of COB is outside the direct Chain of Command, the COB has tremendous authority and responsibility as top enlisted sailor of the vessel.