Third Officer
Third Officer is a rank used by the Royal Manticoran Merchant Marine.
Honorverse
In the Honorverse, a Third Officer is a deck officer holding a Certificate of Competency (Star Empire of Manticore and other star nations) or a License as Third Officer. They also hold an endorsement as Officer In Charge of a Navigation Watch. Third Officers are also known as Third Mates. They are primarily a watch stander, standing watch on the bridge while underway. Their collateral duties include inspection and upkeep of fire fighting equipment and life saving appliances. On a passenger liner, they could be a day worker focusing on inspection and upkeep of the large amount of fire fighting equipment and life saving appliances.
Third Officers are considered Operational Level officers.
TRMN
In TRMN, a Third Officer is a merchant marine deck officer who has 1) completed their Third Officer exam (Line track) or Spacer V exam, and 2) served as a Fourth Officer for twelve months Time In Grade, after which time they are eligible to be promoted to this rank by a promotion board.
Real World
A Third Officer, also known as Third Mate, is a licensed deck officer (US term) or certificated officer (UK term). As a deck officer they also hold an STCW endorsement as Officer In Charge of a Navigation Watch. They are primarily a watch stander, standing watch on the bridge underway. Their collateral duties include inspection and upkeep of fire fighting equipment and life saving appliances. On a cruise ship they could be a day worker focusing on inspection and upkeep of the large amount of fire fighting equipment and life saving appliances.
Third Officers are considered Operational Level officers.