EBarnacle said:

The vessel's captain is variously referred to as Lieutenant, Captain, Commodore.

I don't know for sure about present naval terminology, but it used to be quite possible to be a lieutenant (or a captain) and be a commodore. A commodore is (was) an officer who is not an admiral who is in overall command of a multi-ship mission. He is (was) of at least the same rank and date of rank as the otherwise highest ranking officer in the ships on that mission.

Dave Oesterreich