It has been common since WW2 for big ships to have multiple commanders. Even excepting aircraft carriers, it was common in WW2 for a US battleship or cruiser to have commanders heading gunnery, engineering, navigation, construction, medical and supply departments, and not uncommonly a full commander dentist and/or chaplain as well. A British battleship or cruiser invariably had an engineer commander, usually a paymaster commander as supply officer and frequently a surgeon commander besides "The Commander," the second in command.